Enero de 2017
Ionospheric signatures of gravity waves produced by the 2004 Sumatra and 2011 Tohoku tsunamis: A modeling study
Authors: Yonghui Yu, Wenqing Wang et al
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Abstract
Ionospheric fluctuations inferred from observations of total electron content have previously been attributed to tsunamis and have confirmed the strong coupling between Earth's ocean and ionosphere via atmospheric gravity waves (AGWs). To further advance our understanding of this wave coupling process we employ a linear full-wave model and a nonlinear time-dependent model to examine the ionospheric response to the AGW perturbations induced by the 2004 Sumatra and the 2011
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Tohoku tsunamis. In the 2004 case, our modeling analyses reveal that one component of the propagating AGWs becomes dynamically unstable in the E-region ionosphere at a range exceeding 2000 km in a direction 340° clockwise from north. Another component becomes convectively unstable in the E-region ionosphere at a range exceeding 700 km in a direction 250° clockwise from north. In the 2011 case, a significant enhancement in the ionospheric disturbance occurs in a direction northwest from the epicenter about 1 h following the tsunami onset, in general agreement with observations. Our simulations also indicate that the AGW propagating toward the southeast is responsible for a traveling ionospheric disturbance that remains of an observable amplitude for over 4 h during which time it propagates horizontally almost 4000 km.
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Enero de 2017
Time Reversal Imaging of the 2015 Illapel Tsunami Source
Authors: Chao An and Lingsen Meng
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Abstract
Studies of the 2015 Illapel earthquake show large variance in the east-west location of the principal slip, and it is also controversial if there is significant slip near the trench. In this study, we derive the initial water elevation from tsunami waves based on the time reversal imaging technique. This approach does not make
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assumptions on the fault geometry required by finite-fault inversions. We adopt 4 out of total 24 stations based on their azimuthal coverage in the time reversal analysis. Additionally, we introduce a correction that scales the wave amplitude at each station by the epicentral distance to account for the 2d spreading effects. The results show a focused region of water elevation with a maximum height of 2.0 m located approximately 30 km from the trench. By comparison to the initial deformation predicted by several finite-fault models, our results indicate minimum slip distribution near the trench.
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Enero de 2017
Super-interseismic periods: Redefining earthquake recurrence
Author: John P. Loveless
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Abstract
Precise geodetic measurements made over broad swaths of tectonically active regions record patterns of interseismic strain accumulation,
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providing key insights into the locus and timing of pending earthquakes. Recent studies of geodetic position time series, including that of Melnick et al. [2017] in this issue, illustrate temporal variation in the pattern of interseismic deformation. These authors propose that the 2010 Mw = 8.8 Maule, Chile earthquake enhanced coupling on the Andean subduction zone adjacent to the rupture, including on the portion of the megathrust that broke five years later in the Mw = 8.3 Illapel event.
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Enero de 2017
Reflecting upon 10 Years of Geoengineering Research: Introduction to the Crutzen + 10 Special Issue
Authors: Miranda Boettcher and Stefan Schäfer
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Abstract
Ten years ago, Nobel laureate Paul Crutzen called for research into the possibility of reflecting sunlight away from Earth by injecting sulfur particles into the stratosphere. Across academic disciplines, Crutzen's intervention caused a surge in interest in and research on proposals for what is often referred to as “geoengineering” - an unbounded set of heterogeneous proposals for intentionally intervening into the climate system to reduce the risks of climate change. To mark the 10 year anniversary of the publication of Paul Crutzen's seminal essay, this special issue
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reviews the developments in geoengineering research since Crutzen's intervention and reflects upon possible future directions that geoengineering research may take. In this introduction, we briefly outline the arguments made in Paul Crutzen's 2006 contribution and describe the key developments of the past 10 years. We then proceed to give an overview of some of the central issues in current discussions on geoengineering, and situate the contributions to this special issue within them. In particular, we contend that geoengineering research is characterized by an orientation toward speculative futures that fundamentally shapes how geoengineering is entering the collective imagination of scientists, policymakers, and publics, and a mode of knowledge production that recognizes the risks which may result from new knowledge and that struggles with its own socio-political dimensions.
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Enero de 2017
Global atmospheric response to emissions from a proposed reusable space launch system
Authors: Erik J. L. Larson, Robert W. Portmann et al
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Abstract
Modern reusable launch vehicle technology may allow high flight rate space transportation at low cost. Emissions associated with a hydrogen fueled reusable rocket system are modeled based on the launch requirements of developing a space-based solar power system that generates present-day global electric energy demand. Flight rates from 104 to 106 per year |
are simulated and sustained to a quasisteady state. For the assumed rocket engine, H2O and NOX are the primary emission products; this also includes NOX produced during reentry heating. For a base case of 105 flights per year, global stratospheric and mesospheric water vapor increase by approximately 10 and 100%, respectively. As a result, high-latitude cloudiness increases in the lower stratosphere and near the mesopause by as much as 20%. Increased water vapor also results in global effective radiative forcing of about 0.03 W/m2. NOX produced during reentry exceeds meteoritic production by more than an order of magnitude, and along with in situ stratospheric emissions, results in a 0.5% loss of the globally averaged ozone column, with column losses in the polar regions exceeding 2%. |
Enero de 2017
T-phase and tsunami pressure waveforms recorded by near-source IMS water-column hydrophone triplets during the 2015 Chile earthquake
Authors: H. Matsumoto, G. Haralabus et al
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Abstract
Underwater acoustic signal waveforms recorded during the 2015 Chile earthquake (Mw 8.3) by the hydrophones of hydroacoustic station HA03, located at the Juan Fernandez Islands, are analyzed. HA03 is part of the Comprehensive Nuclear-Test-Ban Treaty International Monitoring System. The interest in the particular data set stems from the fact that HA03 is located only approximately 700 km SW from the epicenter of
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the earthquake. This makes it possible to study aspects of the signal associated with the tsunamigenic earthquake, which would be more difficult to detect had the hydrophones been located far from the source. The analysis shows that the direction of arrival of the T phase can be estimated by means of a three-step preprocessing technique which circumvents spatial aliasing caused by the hydrophone spacing, the latter being large compared to the wavelength. Following this preprocessing step, standard frequency-wave number analysis (F-K analysis) can accurately estimate back azimuth and slowness of T-phase signals. The data analysis also shows that the dispersive tsunami signals can be identified by the water-column hydrophones at the time when the tsunami surface gravity wave reaches the station. |
Enero de 2017
On different approaches to modeling
Author: Yehuda Ben-Zion
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Abstract
A number of years ago, during a geophysics meeting in Erice, Sicily, Rick Sibson provided the following perceptive observation on a typical relation between the geological complexity of a given situation and the complexity of the corresponding mathematical modeling, Geol Complx * Math Complx aprox 1
This statement summarizes two end-member cases of modeling that can be illustrated with examples from mechanics of faulting. On one
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hand, highly complex multiphysics/chemistry processes in heterogeneous crustal-scale structures are often analyzed with back-of-the-envelope approximations and simple terms such as dislocations on a planar surface in a homogeneous solid. On the other hand, far simpler engineered rock samples in laboratory experiments under controlled conditions are often analyzed with elaborate mathematical models of complex constitutive laws having many parameters and variables. As noted by the statistician George Box, “all models are wrong but some are useful.” The question, keeping in mind Sibson's observation, is which models are useful in what circumstances. The answer depends on whether one is interested in engineering applications or scientific understanding. |
Enero de 2017
Impact of social preparedness on flood early warning systems
Authors: M. Girons Lopez, G. Di Baldassarre et al
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Abstract
Flood early warning systems play a major role in the disaster risk reduction paradigm as cost-effective methods to mitigate flood disaster damage. The connections and feedbacks between the hydrological and social spheres of early warning systems are increasingly being considered as key aspects for successful flood mitigation. The behavior of the public and first responders during flood situations, determined by their preparedness, is heavily influenced by many
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behavioral traits such as perceived benefits, risk awareness, or even denial. In this study, we use the recency of flood experiences as a proxy for social preparedness to assess its impact on the efficiency of flood early warning systems through a simple stylized model and implemented this model using a simple mathematical description. The main findings, which are based on synthetic data, point to the importance of social preparedness for flood loss mitigation, especially in circumstances where the technical forecasting and warning capabilities are limited. Furthermore, we found that efforts to promote and preserve social preparedness may help to reduce disaster-induced losses by almost one half. The findings provide important insights into the role of social preparedness that may help guide decision-making in the field of flood early warning systems. |
Enero de 2017
Cumulative Hazard: The Case of Nuisance Flooding
Authors: Hamed R. Moftakhari, Amir AghaKoucha et al
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Abstract
The cumulative cost of frequent events (e.g., nuisance floods) over time may exceed the costs of the extreme but infrequent events for which societies typically prepare. Here we analyze the likelihood of exceedances above mean higher high water and the corresponding property value exposure for minor, major and extreme coastal floods. Our results suggest that, in response to sea-level rise, nuisance flooding could generate
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property value exposure comparable to, or larger than, extreme events. Determining whether (and when) low cost, nuisance incidents aggregate into high cost impacts and deciding when to invest in preventive measures are amongst the most difficult decisions for policy-makers. It would be unfortunate if efforts to protect societies from extreme events (e.g., 0.01 annual probability) left them exposed to a cumulative hazard with enormous costs. We propose a Cumulative Hazard Index (CHI) as a tool for framing the future cumulative impact of low cost incidents relative to infrequent extreme events. CHI suggests that in New York, NY, Washington, DC, Miami, FL, San Francisco, CA and Seattle, WA, a careful consideration of socio-economic impacts of nuisance flooding for prioritization is crucial for sustainable coastal flood risk management. |
Enero de 2017
Global geodynamic changes induced by all major earthquakes, 1976–2015
Authors: Benjamin F Chao and Hao Ding
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Abstract
Using normal-mode summations we calculate the coseismic changes in a suite of global geodynamic quantities produced by all the 43,304 major earthquakes that occurred during 1976–2015 from the Global Centroid Moment Tensor catalogue. We calculate changes for the Earth's inertia tensor elements and the ensuing Earth's rotation variations, as well as the monopolar changes of the volume ?V(r), the total moment of inertia ?T(r), and the gravitational energy ?Eg(r) as functions of the radius inside the Earth. The cumulative geodynamic changes are found to have strong statistical trends that are continuing from the past and further strengthened in recent years. Statistical analyses indicate that |
the thrust-faulting earthquakes are predominantly responsible for these trends, as they are the dominant type overshadowing the normal-faulting earthquakes that tend to produce the opposite effects. In particular, we report that the polar motion excitations due to the few greatest earthquakes since 2004 have facilitated the abrupt turn of the pole path observed during these years. For the monopolar parameters, we find an overall shrinkage in Earth's volume V(r) internally but an expansion near Earth's surface. The ensuing gravitational instability cannot be sustained over time and will be reversed by aseismic and interseismic deformations. The ?T(r) and ?Eg(r) also exhibit trends where the coseismic action of earthquakes collectively makes the Earth more compact and dissipate a great amount of gravitational energy. Although aseismic effects are not addressed here, these coseismic trends are in keeping with the long-term physical evolution of the Earth. |
Enero de 2017
Reexamination of the magnitudes for the 1906 and 1922 Chilean earthquakes using Japanese tsunami amplitudes: Implications for source depth constraints
Authors: M Carvajal, M Cisternas et al
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Abstract
Far-field tsunami records from the Japanese tide gauge network allow the reexamination of the moment magnitudes (Mw) for the 1906 and 1922 Chilean earthquakes, which to date rely on limited information mainly from seismological observations alone. Tide gauges along the Japanese coast provide extensive records of tsunamis triggered by six great (Mw >8) Chilean earthquakes with instrumentally determined moment magnitudes. These tsunami records are used to explore the dependence of tsunami amplitudes in Japan on the parent earthquake magnitude of Chilean origin. Using the resulting regression parameters together with tide gauge |
amplitudes measured in Japan we estimate apparent moment magnitudes of Mw 8.0–8.2 and Mw 8.5–8.6 for the 1906 central and 1922 north- central Chile earthquakes. The large discrepancy of the 1906 magnitude estimated from the tsunami observed in Japan as compared with those previously determined from seismic waves (Ms 8.4) suggests a deeper than average source with reduced tsunami excitation. A deep dislocation along the Chilean megathrust would favor uplift of the coast rather than beneath the sea, giving rise to a smaller tsunami and producing effects consistent with those observed in 1906. The 1922 magnitude inferred from far-field tsunami amplitudes appear to better explain the large extent of damage and the destructive tsunami that were locally observed following the earthquake than the lower seismic magnitudes (Ms 8.3) that were likely affected by the well-known saturation effects. Thus, a repeat of the large 1922 earthquake poses seismic and tsunami hazards in a region identified as a mature seismic gap. |
Enero de 2017
Illusion and Reality in the Atmospheres of Exoplanets
Authors: L. Drake Deming and Sara Seager
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Abstract
The atmospheres of exoplanets reveal all their properties beyond mass, radius, and orbit. Based on bulk densities, we know that exoplanets as small as 1.5 Earth radii must have gaseous envelopes, hence atmospheres. We discuss contemporary techniques for characterization of exoplanetary atmospheres. The measurements are difficult, because - even in current favorable cases - the signals can be as small as 0.001% of the host star's flux. Consequently, some early results have been illusory, and not confirmed by subsequent investigations. Prominent illusions to date include polarized scattered light, temperature inversions, and the existence of carbon planets. The field moves from the first tentative and often
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incorrect conclusions, converging to the reality of exoplanetary atmospheres. That reality is revealed using transits for close-in exoplanets, and direct imaging for young or massive exoplanets in distant orbits. Several atomic and molecular constituents have now been robustly detected in exoplanets as small as Neptune. In our current observations, the effects of clouds and haze appear ubiquitous. Topics at the current frontier include the measurement of heavy element abundances in giant planets, detection of carbon-based molecules, measurement of atmospheric temperature profiles, definition of heat circulation efficiencies for tidally-locked planets, and the push to detect and characterize the atmospheres of super-Earths. Future observatories for this quest include the James Webb Space Telescope, and the new generation of Extremely Large Telescopes on the ground. On a more distant horizon, NASA's plans for the HabEx and LUVOIR missions could extend the study of exoplanetary atmospheres to true twins of Earth. |
Enero de 2017
Detailed Spatio-Temporal Evolution of Microseismicity and Repeating Earthquakes following the 2012 Mw7.6 Nicoya Earthquake
Authors: Dongdong Yao, Jacob I. Walter et al
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Abstract
We apply a waveform matching technique to obtain a detailed earthquake catalog around the rupture zone of the 5 September 2012 moment magnitude 7.6 Nicoya earthquake, with emphasis on its aftershock sequence. Starting from a preliminary catalog, we relocate ~7,900 events using TomoDD to better quantify their spatio-temporal behavior. Relocated aftershocks are mostly clustered in two groups. The first is immediately above the major coseismic slip patch, partially overlapping with shallow afterslip. The second one is 50 km SE to the mainshock nucleation point and near the terminus of coseismic rupture, in a zone that exhibited little resolvable afterslip. Using the relocated events as
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templates, we scan through the continuous recording from 29 June 2012 to 30 December 2012, detecting approximately 17 times more than template events. We find 190 aftershocks in the first half hour following the mainshock, mostly along the plate interface. Later events become more scattered in location, showing moderate expansion in both along-trench and down-dip directions. From the detected catalog we identify 53 repeating aftershock clusters with mean cross-correlation values larger than 0.9, and indistinguishably intra-cluster event locations, suggesting slip on the same fault patch. Most repeating clusters occurred within the first major aftershock group. Very few repeating clusters were found in the aftershock grouping along the southern edge of the Peninsula, which is not associated with substantial afterslip. Our observations suggest that loading from nearby afterslip along the plate interface drives spatio-temporal evolution of aftershocks just above the mainshock rupture patch, while aftershocks in the SE group are to the SE of the observed updip afterslip and poorly constrained. |
Enero de 2017
On the secular retention of ground water and ice on Mars
Authors: Robert E. Grimm, Keith P. Harrison et al
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Abstract
Tropical ground ice on Mars undergoes long-term sublimation and likely exospheric escape. Without restriction of sublimation, the cryosphere would eventually breach, leading to massive loss of any underlying groundwater. We seek to understand the conditions under which the ground-ice seal, groundwater, and subsurface habitability are preserved. Using multireservoir models for the evolution of deuterium-to-hydrogen ratios, we derive a median estimate of the Hesperian-Amazonian H2O loss of 60 m (interquartile range 30–120 m) global equivalent layer (GEL), neglecting magmatic degassing. Most of the loss may have been early, with consequent low loss in
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the “modern” cold and dry climate. We modeled global H2O transport within Mars following an assumed abrupt transition to modern conditions at 3 Ga. Sublimation is retarded (in order of decreasing priority) by higher obliquity, smaller porosity, higher tortuosity, lower heat flow, and smaller pore radius. Higher obliquity reduces H2O loss by decreasing tropical surface temperatures and raising global atmospheric water vapor. Time-variable obliquities do not overly influence outcomes as long as the total duration <30° obliquity is <1 Gyr, with no interval longer than a few hundred million years. Decreased solar luminosity or a thicker CO2 atmosphere can also retard loss of subsurface H2O, whereas lower atmospheric water vapor accelerates sublimation. If Mars' post-Noachian crustal H2O inventory was a few hundred meters GEL or more, then the modest loss since then implies that the cryospheric seal has been maintained following top down freezing and that groundwater likely exists globally on Mars today. |
Diciembre de 2016
A new strategy for earthquake focal mechanisms using waveform-correlation-derived relative polarities and cluster analysis: Application to the 2014 Long Valley Caldera earthquake swarm
Authors: David R. Shelly, Jeanne L. Hardebeck et al
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Abstract
In microseismicity analyses, reliable focal mechanisms can typically be obtained for only a small subset of located events. We address this limitation here, presenting a framework for determining robust focal mechanisms for entire populations of very small events. To achieve this, we resolve relative P and S wave polarities between pairs of waveforms by using their signed correlation coefficients—a by-product of previously performed precise earthquake relocation. We then use cluster analysis to group events with similar patterns of polarities across the network. Finally, we apply a standard mechanism inversion to the grouped data, using either catalog or |
correlation-derived P wave polarity data sets. This approach has great potential for enhancing analyses of spatially concentrated microseismicity such as earthquake swarms, mainshock-aftershock sequences, and industrial reservoir stimulation or injection-induced seismic sequences. To demonstrate its utility, we apply this technique to the 2014 Long Valley Caldera earthquake swarm. In our analysis, 85% of the events (7212 out of 8494 located by Shelly et al. [2016]) fall within five well-constrained mechanism clusters, more than 12 times the number with network-determined mechanisms. Of the earthquakes we characterize, 3023 (42%) have magnitudes smaller than 0.0. We find that mechanism variations are strongly associated with corresponding hypocentral structure, yet mechanism heterogeneity also occurs where it cannot be resolved by hypocentral patterns, often confined to small-magnitude events. Small (5–20°) rotations between mechanism orientations and earthquake location trends persist when we apply 3-D velocity models and might reflect a geometry of en echelon, interlinked shear, and dilational faulting. |
Diciembre de 2016
Fault zone controlled seafloor methane seepage in the rupture area of the 2010 Maule earthquake, Central Chile
Authors: Jacob Geersen, Florian Scholz et al
Link: Click here
Abstract
Seafloor seepage of hydrocarbon-bearing fluids has been identified in a number of marine fore arcs. However, temporal variations in seep activity and the structural and tectonic parameters that control the seepage often remain poorly constrained. Subduction zone earthquakes, for example, are often discussed to trigger seafloor seepage but causal links that go beyond theoretical considerations have not yet been fully established. This is mainly due to the inaccessibility of offshore epicentral areas, the infrequent occurrence of large earthquakes, and challenges associated with offshore monitoring of seepage over large areas and sufficient time periods. Here we report visual, geochemical,
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geophysical, and modeling results and observations from the Concepción Methane Seep Area (offshore Central Chile) located in the rupture area of the 2010 Mw. 8.8 Maule earthquake. High methane concentrations in the oceanic water column and a shallow subbottom depth of sulfate penetration indicate active methane seepage. The stable carbon isotope signature of the methane and hydrocarbon composition of the released gas indicate a mixture of shallow-sourced biogenic gas and a deeper sourced thermogenic component. Pristine fissures and fractures observed at the seafloor together with seismically imaged large faults in the marine fore arc may represent effective pathways for methane migration. Upper plate fault activity with hydraulic fracturing and dilation is in line with increased normal Coulomb stress during large plate-boundary earthquakes, as exemplarily modeled for the 2010 earthquake. On a global perspective our results point out the possible role of recurring large subduction zone earthquakes in driving hydrocarbon seepage from marine fore arcs over long timescales. |
Diciembre de 2016
Modeling geomagnetic induction hazards using a 3-D electrical conductivity model of Australia
Authors: Liejun Wang, Andrew M. Lewis et al
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Abstract
The surface electric field induced by external geomagnetic source fields is modeled for a continental-scale 3-D electrical conductivity model of Australia at periods of a few minutes to a few hours. The amplitude and orientation of the induced electric field at periods of 360 s and 1800s are presented and compared to those derived from a simplified ocean-continent (OC) electrical conductivity model. It is found that the induced electric field in the Australian region is distorted by the heterogeneous continental electrical conductivity structures and surrounding
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oceans. On the northern coastlines, the induced electric field is decreased relative to the simple OC model due to a reduced conductivity contrast between the seas and the enhanced conductivity structures inland. In central Australia, the induced electric field is less distorted with respect to the OC model as the location is remote from the oceans, but inland crustal high-conductivity anomalies are the major source of distortion of the induced electric field. In the west of the continent, the lower conductivity of the Western Australia Craton increases the conductivity contrast between the deeper oceans and land and significantly enhances the induced electric field. Generally, the induced electric field in southern Australia, south of latitude −20°, is higher compared to northern Australia. This paper provides a regional indicator of geomagnetic induction hazards across Australia. |
Diciembre de 2016
Ionospheric signatures of gravity waves produced by the 2004 Sumatra and 2011 Tohoku tsunamis: A modeling study
Authors: Yonghui Yu, Wenqing Wang et al
Link: Click here
Abstract
Ionospheric fluctuations inferred from observations of total electron content (TEC) have previously been attributed to tsunamis, and have confirmed the strong coupling between Earth's ocean and ionosphere via atmospheric gravity waves (AGWs). To further advance our understanding of this wave coupling process we employ a linear full-wave model and a nonlinear time-dependent model to examine the ionospheric response to the AGW perturbations induced by the 2004 Sumatra and the 2011
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Tohoku tsunamis. In the 2004 case, our modeling analyses reveal that one component of the propagating AGWs becomes dynamically unstable in the E-region ionosphere at a range exceeding 2000 km in a direction 340o clockwise from north. Another component becomes convectively unstable in the E-region ionosphere at a range exceeding 700 km in a direction 250o clockwise from north. In the 2011 case, a significant enhancement in the ionospheric disturbance occurs in a direction northwest from the epicenter about an hour following the tsunami onset, in general agreement with observations. Our simulations also indicate that the AGW propagating toward the southeast is responsible for a traveling ionospheric disturbance (TID) that remains of an observable amplitude for over four hours during which time it propagates horizontally almost 4000 km. |
Diciembre de 2016
Observation of Tsunami-Generated Ionospheric Signatures over Hawaii caused by the the 16 September 2015 Illapel Earthquake
Authors: Matthew A. Grawe, Jonathan J. Makela et al
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Abstract
Tsunamis generate internal gravity waves (IGWs) that propagate vertically into the atmosphere, and can create detectable signatures in the ionosphere. These signatures have consistently been observed in the presence of a tsunami for over a decade in the total electron content and for over five years in the 630.0-nm airglow. Here, we show perturbations appearing in filtered GPS-derived total electron content (TEC) and 630.0-nm
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airglow above Hawaii during the passing of the tsunami induced by the 16 September 2015 earthquake in Illapel, Chile. We report measurements of IGW parameters from both observation methodologies using a combination of prior methods and a newly developed method that uses a Gabor filter bank. A previously developed geometric model that takes into account the assumed posture of tsunami-induced IGWs in the geomagnetic field and the observation geometry is shown to predict fairly well the expected location of the observation in the sky. Results of the Gabor filtering technique are also compared to previously published results for the 11 March 2011 Tohoku event. An overall comparison between all of the tsunami-induced signatures that have appeared in both the 630.0-nm airglow and TEC above Hawaii to date is provided. |
Diciembre de 2016
Fault activation by hydraulic fracturing in western Canada
Authors: Xuewei Bao and David W. Eaton
Link: Click here
Abstract
Hydraulic fracturing has been inferred to trigger the majority of injection-induced earthquakes in western Canada, in contrast to the Midwestern United States, where massive saltwater disposal is the dominant triggering mechanism. A template-based earthquake catalog from a seismically active Canadian shale play, combined
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with comprehensive injection data during a 4- month interval, shows that earthquakes are tightly clustered in space and time near hydraulic fracturing sites. The largest event [moment magnitude (MW) 3.9] occurred several weeks after injection along a fault that appears to extend from the injection zone into crystalline basement. Patterns of seismicity indicate that stress changes during operations can activate fault slip to an offset distance of >1 km, whereas pressurization by hydraulic fracturing into a fault yields episodic seismicity that can persist for months. |
Diciembre de 2016
Understanding induced seismicity
Authors: Derek Elsworth, Christopher J. Spiers et al
Link: Click here
Abstract
Fluid injection–induced seismicity has become increasingly widespread in oil- and gas-producing areas of the United States (1–3) and western Canada. It has shelved deep geothermal energy projects in Switzerland and the United States (4), and its effects are especially acute in Oklahoma, where seismic hazard is now approaching the tectonic levels of parts of
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California. Unclear in the highly charged debate over expansion of shale gas recovery has been the role of hydraulic fracturing (fracking) in causing increased levels of induced seismicity. Opponents to shale gas development have vilified fracking as directly responsible for this increase in seismicity. However, this purported causal link is not substantiated; the predominant view is that triggering in the midwestern United States is principally a result of massive reinjection of energy-coproduced wastewaters. On page 1406 of this issue, Bao and Eaton (5) identify at least one example of seismicity developed from hydraulic fracturing for shale gas in the Alberta Basin. |
Diciembre de 2016
Large gem diamonds from metallic liquid in Earth’s deep mantle
Authors: Evan M. Smith, Steven B. Shirey et al
Link: Click here
Abstract
The redox state of Earth’s convecting mantle, masked by the lithospheric plates and basaltic magmatism of plate tectonics, is a key unknown in the evolutionary history of our planet. Here we report that large, exceptional gem diamonds like the Cullinan, Constellation, and Koh-i-Noor carry
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direct evidence of crystallization from a redox-sensitive metallic liquid phase in the deep mantle. These sublithospheric diamonds contain inclusions of solidified iron-nickel-carbon-sulfur melt, accompanied by a thin fluid layer of methane ± hydrogen, and sometimes majoritic garnet or former calcium silicate perovskite. The metal-dominated mineral assemblages and reduced volatiles in large gem diamonds indicate formation under metal-saturated conditions. We verify previous predictions that Earth has highly reducing deep mantle regions capable of precipitating a metallic iron phase that contains dissolved carbon and hydrogen. |
Diciembre de 2016
Observation and modeling of gravity wave propagation through reflection and critical layers above Andes Lidar Observatory at Cerro Pachón, Chile
Authors: Bing Cao, Christopher J. Heale et al
Link: Click here
Abstract
A complex gravity wave event was observed from 04:30 to 08:10 UTC on 16 January 2015 by a narrow-band sodium lidar and an all-sky airglow imager located at Andes Lidar Observatory (ALO) in Cerro Pachón (30.25°S, 70.73°W), Chile. The gravity wave packet had a period of 18–35 min and a horizontal wavelength of about 40–50 km. Strong enhancements of the vertical wind perturbation, exceeding 10 m s−1, were found at ∼90 km and ∼103 km, consistent with nearly
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evanescent wave behavior near a reflection layer. A reduction in vertical wavelength was found as the phase speed approached the background wind speed near ∼93 km. A distinct three-layered structure was observed in the lidar data due to refraction of the wave packet. A fully nonlinear model was used to simulate this event, which successfully reproduced the amplitudes and layered structure seen in observations. The model results provide dynamical insight, suggesting that a double reflection occurring at two separate heights caused the large vertical wind amplitudes, while the three-layered structure in the temperature perturbation was a result of relatively stable regions at those altitudes. The event provides a clear perspective on the filtering processes to which short-period, small-scale gravity waves are subject in mesosphere and lower thermosphere.
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Diciembre de 2016
Aquifers switched from confined to semiconfined by earthquakes
Authors: Zheming Shi and Guangcai Wang
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Abstract
Earthquake-induced aquifer parameter changes (e.g., permeability and hydraulic diffusivity) have been documented in many studies. However, changes in the confinement of an aquifer from confined to semiconfined following an earthquake have not been reported. Here we focus on the
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tidal response of the water level in four wells following the 2008 Wenchuan Mw 7.9 and 2013 Lushan Mw 6.6 earthquakes to show that earthquakes can change confined aquifers to semiconfined aquifers by reopening of preexisting vertical fractures (and later healing). This study has important implications because a switch from confined to semiconfined means a change of vertical hydraulic connection, which may affect the vulnerability of an aquifer, the integrity of underground waste repositories, and the safety of groundwater supplies. |
Diciembre de 2016
Optimal time alignment of tide-gauge tsunami waveforms in nonlinear inversions: Application to the 2015 Illapel (Chile) earthquake
Authors: F. Romano, A. Piatanesi et al
Link: Click here
Abstract
Tsunami waveform inversion is often used to retrieve information about the causative seismic tsunami source. Tide gauges record tsunamis routinely; however, compared to deep-ocean sensor data, tide-gauge waveform modeling is more difficult due to coarse/inaccurate local bathymetric models resulting in a time mismatch
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between observed and predicted waveforms. This can affect the retrieved tsunami source model, thus limiting the use of tide-gauge data. A method for nonlinear inversion with an automatic optimal time alignment (OTA), calculated by including a time shift parameter in the cost function, is presented. The effectiveness of the method is demonstrated through a series of synthetic tests and is applied as part of a joint inversion with interferometric synthetic aperture radar data for the slip distribution of the 2015 Mw 8.3 Illapel earthquake. The results show that without OTA, the resolution on the slip model degrades significantly and that using this method for a real case strongly affects the retrieved slip pattern. |
Diciembre de 2016
Fault zone controlled seafloor methane seepage in the rupture area of the 2010 Maule earthquake, Central Chile
Authors: Jacob Geersen, Florian Scholz et al
Link: Click here
Abstract
Seafloor seepage of hydrocarbon-bearing fluids has been identified in a number of marine fore arcs. However, temporal variations in seep activity and the structural and tectonic parameters that control the seepage often remain poorly constrained. Subduction zone earthquakes, for example, are often discussed to trigger seafloor seepage but causal links that go beyond theoretical considerations have not yet been fully established. This is mainly due to the inaccessibility of offshore epicentral areas, the infrequent occurrence of large earthquakes, and challenges associated with offshore monitoring of seepage over large areas and sufficient time periods. Here we report visual, geochemical, geophysical, and modeling results and
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observations from the Concepción Methane Seep Area (offshore Central Chile) located in the rupture area of the 2010 Mw. 8.8 Maule earthquake. High methane concentrations in the oceanic water column and a shallow subbottom depth of sulfate penetration indicate active methane seepage. The stable carbon isotope signature of the methane and hydrocarbon composition of the released gas indicate a mixture of shallow-sourced biogenic gas and a deeper sourced thermogenic component. Pristine fissures and fractures observed at the seafloor together with seismically imaged large faults in the marine fore arc may represent effective pathways for methane migration. Upper plate fault activity with hydraulic fracturing and dilation is in line with increased normal Coulomb stress during large plate-boundary earthquakes, as exemplarily modeled for the 2010 earthquake. On a global perspective our results point out the possible role of recurring large subduction zone earthquakes in driving hydrocarbon seepage from marine fore arcs over long timescales.
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Noviembre de 2016
Mega-earthquakes rupture flat megathrusts
Authors: Quentin Bletery, Amanda M. Thomas et al
Link: Click here
Abstract
Megathrust faults in subduction zones cause large and damaging earthquakes. Bletery et al. argue that certain geometric features of the subduction zones relate to earthquake size. The key parameter is the curvature of the megathrust. Larger earthquakes occur where the subducting slab is flatter, providing a rough metric for estimating where mega-earthquakes may occur in the future. |
The 2004 Sumatra-Andaman and 2011 Tohoku-Oki earthquakes highlighted gaps in our understanding of mega-earthquake rupture processes and the factors controlling their global distribution: A fast convergence rate and young buoyant lithosphere are not required to produce mega-earthquakes. We calculated the curvature along the major subduction zones of the world, showing that mega-earthquakes preferentially rupture flat (low-curvature) interfaces. A simplified analytic model demonstrates that heterogeneity in shear strength increases with curvature. Shear strength on flat megathrusts is more homogeneous, and hence more likely to be exceeded simultaneously over large areas, than on highly curved faults. |
Noviembre de 2016
3-D high-speed imaging of volcanic bomb trajectory in basaltic explosive eruptions
Authors: D. Gaudin, J. Taddeucci et al
Link: Click here
Abstract
Imaging, in general, and high speed imaging in particular are important emerging tools for the study of explosive volcanic eruptions. However, traditional 2-D video observations cannot measure volcanic ejecta motion toward and away from the camera, strongly hindering our capability to fully determine crucial hazard-related parameters such as explosion directionality and pyroclasts' absolute velocity. In this paper, we use up to three synchronized high-speed cameras to |
reconstruct pyroclasts trajectories in three dimensions. Classical stereographic techniques are adapted to overcome the difficult observation conditions of active volcanic vents, including the large number of overlapping pyroclasts which may change shape in flight, variable lighting and clouding conditions, and lack of direct access to the target. In particular, we use a laser rangefinder to measure the geometry of the filming setup and manually track pyroclasts on the videos. This method reduces uncertainties to 10° in azimuth and dip angle of the pyroclasts, and down to 20% in the absolute velocity estimation. We demonstrate the potential of this approach by three examples: the development of an explosion at Stromboli, a bubble burst at Halema'uma'u lava lake, and an in-flight collision between two bombs at Stromboli. |
Noviembre de 2016
Aquifers switched from confined to semiconfined by earthquakes
Authors: Zheming Shi, Guangcai Wang et al
Link: Click here
Abstract
Earthquake-induced aquifer parameter changes (e.g., permeability and hydraulic diffusivity) have been documented in many studies. However, changes in the confinement of an aquifer from confined to semiconfined following an earthquake have not been reported. Here we focus on the |
tidal response of the water level in four wells following the 2008 Wenchuan Mw 7.9 and 2013 Lushan Mw 6.6 earthquakes to show that earthquakes can change confined aquifers to semiconfined aquifers by reopening of preexisting vertical fractures (and later healing). This study has important implications because a switch from confined to semiconfined means a change of vertical hydraulic connection, which may affect the vulnerability of an aquifer, the integrity of underground waste repositories, and the safety of groundwater supplies. |
Noviembre de 2016
Magnitude-based discrimination of man-made seismic events from naturally occurring earthquakes in Utah, USA
Authors: Keith D. Koper, James C. Pechmann et al
Link: Click here
Abstract
We investigate using the difference between local (ML) and coda/duration (MC) magnitude to discriminate man-made seismic events from naturally occurring tectonic earthquakes in and around Utah. For 6846 well-located earthquakes in the Utah region, we find that ML-MC is on average 0.44 magnitude units smaller for mining- |
induced seismicity (MIS) than for tectonic seismicity (TS). Our interpretation of this observation is that MIS occurs within near-surface low-velocity layers that act as a waveguide and preferentially increase coda duration relative to peak amplitude, while the vast majority of TS occurs beneath the near-surface waveguide. A second data set of 3723 confirmed or probable explosions in the Utah region also has significantly lower ML-MC values than TS, likely for the same reason as the MIS. These observations suggest that ML-MC is useful as a depth indicator and could discriminate small explosions and mining-induced earthquakes from deeper, naturally occurring earthquakes at local-to-regional distances. |
Noviembre de 2016
Ionospheric detection and localization of volcano eruptions on the example of the April 2015 Calbuco events
Authors: Ksenia Shults, Elvira Astafyeva et al
Link: Click here
Abstract
Using data from ground-based Global Navigation Satellite Systems (GNSS) receivers located in southern Chile, we study the ionospheric total electron content (TEC) response to two eruptions of the Calbuco volcano that occurred on 22–23 April 2015. In both cases, the TEC response showed quasi-periodic signals with several consecutive wave trains. The averaged amplitude of the observed covolcanic TEC perturbations amounted 0.45 total electron content unit, 1 TECU = 1016 el m−2 (TECU) for the first eruption and 0.16 TECU for the second one. We compare amplitudes of the TEC response to |
volcano eruptions of different intensity from our and previously published data, and we show that both the intensity and the background ionospheric conditions define the amplitude of ionospheric covolcanic disturbances. The relative contribution, however, scales with the eruption intensity. The traveltime diagrams allowed to estimate the propagation speed of the observed covolcanic TEC perturbations as ~900–1200 m/s, which is close to the acoustic (or shock acoustic) waves speed at the ionospheric height. The spectrograms are consistent with the conclusion on the acoustic nature of the observed TEC perturbations. Finally, we use the approximation of a spherical wave propagating at a constant velocity from a point source, and for the first time, we calculate the location of the volcanic source and the onset time of the volcano eruption from ionospheric measurements. We show that even from 30 s ionospheric GPS data it is possible to “localize” the eruptive source within several degrees of latitude/longitude |
Octubre de 2016
Novel determination of radon-222 velocity in deep subsurface rocks and the feasibility to using radon as an earthquake precursor
Authors: Hovav Zafrir, Yochai Ben Horin et al
Link: Click here
Abstract
A novel technique utilizing simultaneous radon monitoring by gamma and alpha detectors to differentiate between the radon climatic driving forces and others has been improved and used for deep subsurface investigation. Detailed long-term monitoring served as a proxy for studying |
radon movement within the shallow and deep subsurface, as well as for analyzing the effect of various parameters of the radon transport pattern. The main achievements of the investigation are (a) determination, for the first time, of the radon movement velocity within rock layers at depths of several tens of meters, namely, 25 m/h on average; (b) distinguishing between the diurnal periodical effect of the ambient temperature and the semidiurnal effect of the ambient pressure on the radon temporal spectrum; and (c) identification of a radon random preseismic anomaly preceding the Nuweiba, M 5.5 earthquake of 27 June 2015 that occurred within Dead Sea Fault Zone. |
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Octubre de 2016
Coseismic slip and afterslip of the 2015 Mw 8.3 Illapel (Chile) earthquake determined from continuous GPS data
Authors: Mahesh N. Shrivastava, Gabriel González et al
Link: Click here
Abstract
We analyzed the coseismic and early postseismic deformation of the 2015, Mw 8.3 Illapel earthquake by inverting 13 continuous GPS time series. The seismic rupture concentrated in a shallow (<20 km depth) and 100 km long asperity, which slipped up to 8 m, releasing a seismic moment of 3.6 × 1021 Nm (Mw = 8.3). After
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43 days, postseismic afterslip encompassed the coseismic rupture. Afterslip concentrated in two main patches of 0.50 m between 20 and 40 km depth along the northern and southern ends of the rupture, partially overlapping the coseismic slip. Afterslip and aftershocks confined to region of positive Coulomb stress change, promoted by the coseismic slip. The early postseismic afterslip was accommodated ~53% aseismically and ~47% seismically by aftershocks. The Illapel earthquake rupture is confined by two low interseismic coupling zones, which coincide with two major features of the subducting Nazca Plate, the Challenger Fault Zone and Juan Fernandez Ridge. |
Octubre de 2016
Cryoseismology
Authors: Evgeny A. Podolskiy and Fabian Walter et al
Link: Click here
Abstract
The last decade witnessed an explosion in yearly number of publications on passive glacier seismology. The seismic signals from a wide range of glacier-related processes fill a broad band of frequencies (from 10−3 to 102 Hz) and moment magnitudes (from M–3 to M7) providing a fresh and unprecedented view on fundamental processes in the cryosphere. New insights into basal motion, iceberg calving, glacier, iceberg, and sea ice dynamics, and precursory signs of |
unstable glaciers and ice structural changes are being discovered with seismological techniques. These observations offer an invaluable foundation for understanding ongoing environmental changes and for future monitoring of ice bodies worldwide. In this review we discuss seismic sources in the cryosphere as well as research challenges for the near future. The field of glacier seismology is evolving so rapidly that some parts of this review will likely soon be outdated. Nevertheless, given an overwhelming number of recent publications and rapidly growing seismic data volumes provided by modern seismic installations in polar and mountain regions, this introduction to cryosphere seismicity aims to serve as a timely and comprehensive reference for glaciologists and seismologists. |
Octubre de 2016
Mars' atmosphere: The sister planet, our statistical twin
Authors: Wilbur Chen, Shaun Lovejoy et al
Link: Click here
Abstract
Satellite-based Martian reanalyses have allowed unprecedented comparisons between our atmosphere and that of our sister planet, underlining various similarities and differences in their respective dynamics. Yet by focusing on large scale structures and deterministic mechanisms they have improved our understanding of the dynamics only over fairly narrow ranges of (near) planetary scales. However, the Reynolds numbers of the flows on both planets are larger than 1011 and dissipation
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only occurs at centimetric (Mars) or millimetric scales (Earth) so that over most of their scale ranges, the dynamics are fully turbulent. In this paper, we therefore examine the high-level, statistical, turbulent laws for the temperature, horizontal wind, and surface pressure, finding that Earth and Mars have virtually identical statistical exponents so that their statistics are very similar over wide ranges. Therefore, it would seem that with the exception of certain aspects of the largest scales (such as the role of dust in atmospheric heating on Mars, or of water in its various phases on Earth), that the nonlinear dynamics are very similar. We argue that this is a prediction of the classical laws of turbulence when extended to planetary scales and that it supports our use of turbulent laws on both planetary atmospheres.
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Octubre de 2016
The sustainability of habitability on terrestrial planets: Insights, questions, and needed measurements from Mars for understanding the evolution of Earth-like worlds
Authors: B. L. Ehlmann, F. S. Anderson et al
Link: Click here
Abstract
What allows a planet to be both within a potentially habitable zone and sustain habitability over long geologic time? With the advent of exoplanetary astronomy and the ongoing discovery of terrestrial-type planets around other stars, our own solar system becomes a key testing ground for ideas about what factors control planetary evolution. Mars provides the solar system's longest record of the interplay of the physical and chemical processes relevant to habitability on an accessible rocky planet with an atmosphere and hydrosphere. Here we review current understanding and update the timeline of key processes in early Mars history. We then draw on knowledge of exoplanets and the other solar system terrestrial planets to identify six broad questions of high importance to the development and sustaining of habitability (unprioritized): (1) Is
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small planetary size fatal? (2) How do magnetic fields influence atmospheric evolution? (3) To what extent does starting composition dictate subsequent evolution, including redox processes and the availability of water and organics? (4) Does early impact bombardment have a net deleterious or beneficial influence? (5) How do planetary climates respond to stellar evolution, e.g., sustaining early liquid water in spite of a faint young Sun? (6) How important are the timescales of climate forcing and their dynamical drivers? Finally, we suggest crucial types of Mars measurements (unprioritized) to address these questions: (1) in situ petrology at multiple units/sites; (2) continued quantification of volatile reservoirs and new isotopic measurements of H, C, N, O, S, Cl, and noble gases in rocks that sample multiple stratigraphic sections; (3) radiometric age dating of units in stratigraphic sections and from key volcanic and impact units; (4) higher-resolution measurements of heat flux, subsurface structure, and magnetic field anomalies coupled with absolute age dating. Understanding the evolution of early Mars will feed forward to understanding the factors driving the divergent evolutionary paths of the Earth, Venus, and thousands of small rocky extrasolar planets yet to be discovered.
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Octubre de 2016
Most computational hydrology is not reproducible, so is it really science?
Authors: Christopher Hutton, Thorsten Wagener et al
Link: Click here
Abstract
Reproducibility is a foundational principle in scientific research. Yet in computational hydrology the code and data that actually produces published results are not regularly made available, inhibiting the ability of the community to reproduce and verify previous findings. In order to
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overcome this problem we recommend that reuseable code and formal workflows, which unambiguously reproduce published scientific results, are made available for the community alongside data, so that we can verify previous findings, and build directly from previous work. In cases where reproducing large-scale hydrologic studies is computationally very expensive and time-consuming, new processes are required to ensure scientific rigor. Such changes will strongly improve the transparency of hydrological research, and thus provide a more credible foundation for scientific advancement and policy support. |
Octubre de 2016
Sharing the cost of river basin adaptation portfolios to climate change: Insights from social justice and cooperative game theory
Author: Corentin Girard, Jean-Daniel Rinaudo et al
Link: Click here
Abstract
The adaptation of water resource systems to the potential impacts of climate change requires mixed portfolios of supply and demand adaptation measures. The issue is not only to select efficient, robust, and flexible adaptation portfolios but also to find equitable strategies of cost allocation among the stakeholders. Our work addresses such cost allocation problems by applying two
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different theoretical approaches: social justice and cooperative game theory in a real case study. First of all, a cost-effective portfolio of adaptation measures at the basin scale is selected using a least-cost optimization model. Cost allocation solutions are then defined based on economic rationality concepts from cooperative game theory (the Core). Second, interviews are conducted to characterize stakeholders' perceptions of social justice principles associated with the definition of alternatives cost allocation rules. The comparison of the cost allocation scenarios leads to contrasted insights in order to inform the decision-making process at the river basin scale and potentially reap the efficiency gains from cooperation in the design of river basin adaptation portfolios. |
Octubre de 2016
Where giant earthquakes may come
Authors: W Marzocchi, L Sandri et al
Link: Click here
Abstract
Giant earthquakes (Mw=8.5) usually occur on the boundary between subducting and overriding plates of converging margins, but it is not yet clear which (if any) subduction zones are more prone to produce such a kind of events. Here we show that subduction zones may have different capabilities to produce giant earthquakes. We analyze the frequency-magnitude distribution of the interplate earthquakes at subduction zones that occurred
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during 1976–2007 and calculate the propensity (defined as the average annual rate) of giant events for about half of the subduction zones. We find that the b value of interplate earthquakes is significantly different among the subduction zones, and out-of-sample giant earthquakes (before 1976 and after 2007) have occurred preferentially in high-propensity areas. Besides the importance for seismic hazard assessment and risk mitigation, our results seem to indicate that a higher seismicity rate does not necessarily imply a higher likelihood to generate giant earthquakes, and the way in which the stress is released at a subduction interface does not change significantly after the occurrence of such events. |
Octubre de 2016
Ionospheric detection and localization of volcano eruptions on the example of the April 2015 Calbuco events
Author: Sebastian Hainzl
Link: Click here
Abstract
Using data from ground-based Global Navigation Satellite Systems (GNSS) receivers located in southern Chile, we study the ionospheric total electron content (TEC) response to two eruptions of the Calbuco volcano that occurred on 22–23 April 2015. In both cases, the TEC response showed quasi-periodic signals with several consecutive wave trains. The averaged amplitude of the observed covolcanic TEC perturbations amounted 0.45?total electron content unit, 1 TECU?=?1016?el?m-2 (TECU) for the first eruption and 0.16?TECU for the second one. We compare amplitudes of the TEC response to
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volcano eruptions of different intensity from our and previously published data, and we show that both the intensity and the background ionospheric conditions define the amplitude of ionospheric covolcanic disturbances. The relative contribution, however, scales with the eruption intensity. The traveltime diagrams allowed to estimate the propagation speed of the observed covolcanic TEC perturbations as ~900–1200?m/s, which is close to the acoustic (or shock acoustic) waves speed at the ionospheric height. The spectrograms are consistent with the conclusion on the acoustic nature of the observed TEC perturbations. Finally, we use the approximation of a spherical wave propagating at a constant velocity from a point source, and for the first time, we calculate the location of the volcanic source and the onset time of the volcano eruption from ionospheric measurements. We show that even from 30?s ionospheric GPS data it is possible to “localize” the eruptive source within several degrees of latitude/longitude. |
Octubre de 2016
Apparent triggering function of aftershocks resulting from rate-dependent incompleteness of earthquake catalogs
Author: Sebastian Hainzl
Link: Click here
Abstract
The onset of the aftershock decay after main shocks is controversial. Physical models predict that the onset time is stress dependent, and catalog analysis shows a clear increase of the c value of the Omori-Utsu law with increasing main shock magnitude. However, earthquake catalogs are known to have variable quality and completeness levels; in particular, they miss events directly after main shocks. Thus, it has been also argued that the delayed onset of
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recorded aftershock activity triggered by large earthquakes is simply an artifact of the time-varying completeness. Here I utilize a recent approach describing the detection probability of earthquakes as function of the actual earthquake rate. I derive an analytical relation between apparent and true earthquake rate which only depends on the blind time of detection algorithms after the occurrence of an earthquake. This relation is tested and verified for synthetic simulations of Omori-type aftershock sequences. For a comparison, I analyze earthquake sequences occurred in Southern California and Taiwan, finding that the derived analytical decay function consistently explains the empirical aftershock activity in the catalogs. This indicates that the observed scaling of the Omori c value is mainly related to catalog incompleteness and not to any underlying physical process. |
Octubre de 2016
New perspectives on self-similarity for shallow thrust earthquakes
Authors: Marine A. Denolle and Peter M. Shearer et al
Link: Click here
Abstract
Scaling of dynamic rupture processes from small to large earthquakes is critical to seismic hazard assessment. Large subduction earthquakes are typically remote, and we mostly rely on teleseismic body waves to extract information on their slip rate functions. We estimate the P wave source spectra of 942 thrust earthquakes of magnitude Mw 5.5 and above by carefully removing wave propagation effects (geometrical spreading, attenuation, and free surface effects). The conventional spectral model of a single-corner frequency and high-frequency falloff rate does not explain our data, and we instead
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introduce a double-corner-frequency model, modified from the Haskell propagating source model, with an intermediate falloff of f−1. The first corner frequency f1 relates closely to the source duration T1, its scaling follows inline image for Mw<7.5, and changes to inline image for larger earthquakes. An elliptical rupture geometry better explains the observed scaling than circular crack models. The second time scale T2 varies more weakly with moment, inline image, varies weakly with depth, and can be interpreted either as expressions of starting and stopping phases, as a pulse-like rupture, or a dynamic weakening process. Estimated stress drops and scaled energy (ratio of radiated energy over seismic moment) are both invariant with seismic moment. However, the observed earthquakes are not self-similar because their source geometry and spectral shapes vary with earthquake size. We find and map global variations of these source parameters. |
Octubre de 2016
Slip distribution of the 2014 Mw=8.1 Pisagua, northern Chile, earthquake sequence estimated from coseismic fore-arc surface cracks
Authors: John P. Loveless, Chelsea P. Scott et al
Link: Click here
Abstract
The 2014 Mw=8.1 Iquique (Pisagua), Chile, earthquake sequence ruptured a segment of the Nazca-South America subduction zone that last hosted a great earthquake in 1877. The sequence opened >3700 surface cracks in the fore arc of decameter-scale length and millimeter-to centimeter-scale aperture. We use the strikes of measured cracks, inferred to be perpendicular to |
coseismically applied tension, to estimate the slip distribution of the main shock and largest aftershock. The slip estimates are compatible with those based on seismic, geodetic, and tsunami data, indicating that geologic observations can also place quantitative constraints on rupture properties. The earthquake sequence ruptured between two asperities inferred from a regional-scale distribution of surface cracks, interpreted to represent a modal or most common rupture scenario for the northern Chile subduction zone. We suggest that past events, including the 1877 earthquake, broke the 2014 Pisagua source area together with adjacent sections in a throughgoing rupture. |
Octubre de 2016
Localized seismic deformation in the upper mantle revealed by dense seismic arrays
Authors: Asaf Inbal, Jean Paul Ampuero et al
Link: Click here
Abstract
Seismicity along continental transform faults is usually confined to the upper half of the crust, but the Newport-Inglewood fault (NIF), a major fault traversing the Los Angeles basin, is seismically active down to the upper mantle. We use seismic array analysis to illuminate the seismogenic root
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of the NIF beneath Long Beach, California, and identify seismicity in an actively deforming localized zone penetrating the lithospheric mantle. Deep earthquakes, which are spatially correlated with geochemical evidence of a fluid pathway from the mantle, as well as with a sharp vertical offset in the lithosphere-asthenosphere boundary, exhibit narrow size distribution and weak temporal clustering. We attribute these characteristics to a transition from strong to weak interaction regimes in a system of seismic asperities embedded in a ductile fault zone matrix. |
Septiembre de 2016
Validating induced seismicity forecast models—Induced Seismicity Test Bench
Authors: Eszter Király-Proag, J. Douglas Zechar et al
Link: Click here
Abstract
Induced earthquakes often accompany fluid injection, and the seismic hazard they pose threatens various underground engineering projects. Models to monitor and control induced seismic hazard with traffic light systems should be probabilistic, forward-looking, and updated as new data arrive. In this study, we propose an Induced Seismicity Test Bench to test and rank such models; this test bench can be used for model development, model selection, and ensemble model building. We apply the test |
bench to data from the Basel 2006 and Soultz-sous-Forêts 2004 geothermal stimulation projects, and we assess forecasts from two models: Shapiro and Smoothed Seismicity (SaSS) and Hydraulics and Seismics (HySei). These models incorporate a different mix of physics-based elements and stochastic representation of the induced sequences. Our results show that neither model is fully superior to the other. Generally, HySei forecasts the seismicity rate better after shut-in but is only mediocre at forecasting the spatial distribution. On the other hand, SaSS forecasts the spatial distribution better and gives better seismicity rate estimates before shut-in. The shut-in phase is a difficult moment for both models in both reservoirs: the models tend to underpredict the seismicity rate around, and shortly after, shut-in. |
Septiembre de 2016
Low Stress Drop Earthquakes in the Rupture Zone of the 1992 Nicaragua Tsunami Earthquake
Authors: Susan L. Bilek, Holly M. M. Rotman et al
Link: Click here
Abstract
Tsunami earthquakes, events that generate larger than expected tsunami and are deficient in high frequency seismic radiation, are rare but hazardous to coastal populations. One model for these events is shallow rupture through low strength materials. We calculate seismic moment, corner frequency, and stress drop for
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216 earthquakes (2.1?<?Mw?<?4.7, November 2005-June 2006) within and external to the 1992 Nicaragua tsunami earthquake rupture zone to test the hypothesis that differences in fault zone properties defined the limits of the 1992 tsunami rupture zone and continue to produce spatial variations in earthquake source properties. Mean stress drop of events within the rupture area is 1.2?MPa, and 5.5?MPa for events just outside of the rupture zone, with similar magnitude earthquakes in each group. Our results demonstrate different source parameter characteristics for microseismicity in the region of a past tsunami earthquake. |
Septiembre de 2016
MyShake: Initial observations from a global smartphone seismic network
Authors: Qingkai Kong, Richard M. Allen et al
Link: Click here
Abstract
MyShake is a global smartphone seismic network that harnesses the power of crowdsourcing. In the first 6?months since the release of the MyShake app, there were almost 200,000 downloads. On a typical day about 8000 phones provide acceleration waveform data to the MyShake archive. The on-phone app can detect and trigger
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on P waves and is capable of recording magnitude 2.5 and larger events. More than 200 seismic events have been recorded so far, including events in Chile, Argentina, Mexico, Morocco, Nepal, New Zealand, Taiwan, Japan, and across North America. The largest number of waveforms from a single earthquake to date comes from the M5.2 Borrego Springs earthquake in Southern California, for which MyShake collected 103 useful three-component waveforms. The network continues to grow with new downloads from the Google Play store everyday and expands rapidly when public interest in earthquakes peaks such as during an earthquake sequence. |
Septiembre de 2016
Where do ocean microseisms come from? A study of Love-to-Rayleigh wave ratios
Authors: C. Juretzek and C. Hadziioannou et al
Link: Click here
Abstract
Our knowledge of the origin of Love waves in the ambient seismic noise is extremely limited. This applies in particular to constraints on source locations and source mechanisms for Love waves in the secondary microseism. Here three-component beamforming is used to distinguish between the differently polarized wave types in the primary and secondary microseismic noise fields, recorded at several arrays across Europe. We compare characteristics of Love and Rayleigh wave noise, such as source directions and
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frequency content, measure Love to Rayleigh wave ratios for different back azimuths, and look at the seasonal behavior of our measurements by using a full year of data in 2013. The beamforming results confirm previous observations that back azimuths for Rayleigh and Love waves in both microseismic bands mainly coincide. However, we observe differences in relative directional noise strength between both wave types for the primary microseism. At those frequencies, Love waves dominate on average, with kinetic Love-to-Rayleigh energy ratios ranging from 0.6 to 2.0. In the secondary microseism, the ratios are lower, between 0.4 and 1.2. The wave type ratio is directionally homogeneous, except for locations far from the coast. In the primary microseism, our results support the existence of different generation mechanisms. The contribution of a shear traction-type source mechanism is likely. |
Septiembre de 2016
Rapid reinflation following the 2011–2012 rhyodacite eruption at Cordón Caulle volcano (Southern Andes) imaged by InSAR: Evidence for magma reservoir refill
Authors: Francisco Delgado, Matthew E. Pritchard et al
Link: Click here
Abstract
Cordón Caulle is a large fissural volcano that has erupted rhyodacitic magma of the same composition in its past three historical eruptions in 1921, 1960, and 2011–2012. There was significant ground deformation observed before and during the 2011–2012 eruption—here we use |
C and X band interferometric synthetic aperture radar (InSAR) time series results to document posteruptive uplift up to 0.8?m between March 2012 and May 2015, with line-of-sight rates up to 45?cm/yr that have been largely aseismic, along with subsidence in the 2011–2012 lava flow. The 2012 uplift rate is one of the largest for silicic systems and was likely produced by the intrusion of ~0.125?km3 of magma in the same tectonically controlled plumbing system that has been active during the historical eruptions. Nevertheless, the uplift ended before the reservoir refilled with the erupted volume, maybe due to a change in the pressure gradient produced by the 2011–2012 eruption. |
Septiembre de 2016
Where Giant Earthquakes May Come
Authors: W. Marzocchi, L. Sandri et al
Link: Click here
Abstract
Giant earthquakes (MW=8.5) usually occur on the boundary between subducting and overriding plates of converging margins, but it is not yet clear which (if any) subduction zones are more prone to produce such a kind of events. Here we show that subduction zones may have different capabilities to produce giant earthquakes. We analyze the frequency-magnitude distribution of the interplate earthquakes at subduction zones that occurred
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during 1976-2007, and calculate the propensity (defined as the average annual rate) of giant events for about half of the subduction zones. We find that the b-value of interplate earthquakes is significantly different among the subduction zones, and out-of-sample giant earthquakes (before 1976 and after 2007) have occurred preferentially in high propensity areas. Besides the importance for seismic hazard assessment and risk mitigation, our results seems to indicate that a higher seismicity rate does not necessarily implies a higher likelihood to generate giant earthquakes, and the way in which the stress is released at subduction interface does not change significantly after the occurrence of such events. |
Septiembre de 2016
An improvement of the fractal theory and its application in pore structure evaluation and permeability estimation
Authors: Xinmin Ge, Yiren Fan et al
Link: Click here
Abstract
We present an improved fractal model for pore structure evaluation and permeability estimation based on the high pressure mercury porosimetry data. An accumulative fractal equation is introduced to characterize the piecewise nature of the capillary pressure and the mercury saturation. The iterative truncated singular value decomposition algorithm is developed to solve the accumulative fractal equation and obtain the fractal dimension distributions. Furthermore, the
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fractal dimension distributions and relevant parameters are used to characterize the pore structure and permeability. The results demonstrate that the proposed model provides better characterization of the mercury injection capillary pressure than conventional monofractal theory. In addition, there is a direct relationship between the pore structure types and the fractal dimension spectrums. What is more, the permeability is strongly correlated with the geometric and the arithmetic mean values of fractal dimensions, and the permeability estimated using these new fractal dimension parameters achieve excellent result. The improved model and solution give a fresh perspective of the conventional monofractal theory, which may be applied in many geological and geophysical fields. |
Septiembre de 2016
The Subduction Zone Observatory takes shape
Author: Julia Rosen
Link: Click here
Abstract
Depending on how you count, there are roughly a dozen subduction zones around the globe, regions where ocean crust is dragged down into Earth along plate boundaries, leading to large earthquakes and melting in the mantle that causes magma to burble up. Subduction zones
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not only pose a threat to humans, but also act as critical gears in the rock cycle, recycling crust into Earth's interior and pumping up new volcanic rock. Scientists are now cooking up a plan for a major new research program: the Subduction Zone Observatory (SZO). Just where the SZO will be located, what instruments it will include, and what it might cost will come into focus during a National Science Foundation (NSF)–sponsored workshop next week. But many think the observatory could be NSF's next major investment in earth science research, following the $200 million EarthScope project, which began in 2003. |
Septiembre de 2016
Tomography reveals buoyant asthenosphere accumulating beneath the Juan de Fuca plate
Authors: William B. Hawley, Richard M. Allen et al
Link: Click here
Abstract
The boundary between Earth’s strong lithospheric plates and the underlying mantle asthenosphere corresponds to an abrupt seismic velocity decrease and electrical conductivity increase with depth, perhaps indicating a thin, weak layer that may strongly influence plate motion dynamics.
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The behavior of such a layer at subduction zones remains unexplored. We present a tomographic model, derived from on- and offshore seismic experiments, that reveals a strong low-velocity feature beneath the subducting Juan de Fuca slab along the entire Cascadia subduction zone. Through simple geodynamic arguments, we propose that this low-velocity feature is the accumulation of material from a thin, weak, buoyant layer present beneath the entire oceanic lithosphere. The presence of this feature could have major implications for our understanding of the asthenosphere and subduction zone dynamics. |
Septiembre de 2016
The Sustainability of Habitability on Terrestrial Planets: Insights, Questions, and Needed Measurements from Mars for Understanding the Evolution of Earth-like Worlds
Authors: B. L. Ehlmann, F. S. Anderson et al
Link: Click here
Abstract
With the advent of exoplanetary astronomy and the ongoing discovery of terrestrial-type planets around other stars, our own solar system becomes a key testing ground for ideas about what factors control planetary evolution. In particular, what allows a planet to be both within a potentially habitable zone and sustain habitability over long geologic time, are crucial issues. In this regard, Mars is uniquely suited, providing the solar system's longest record of the interplay of the physical and chemical processes relevant to habitability on an accessible rocky planet with an atmosphere and hydrosphere. Here we review current understanding and update the timeline of key processes in early Mars history. We then draw on knowledge of exoplanets and the other solar system terrestrial planets to identify 6 broad questions of high importance to the development and sustaining of habitability (unprioritized): (1) Is
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small planetary size fatal? (2) How do magnetic fields influence atmospheric evolution? (3) To what extent does starting composition dictate subsequent evolution, including redox processes and the availability of water and organics? (4) Does early bombardment during an era of higher impact flux have a net deleterious or beneficial influence? (5) How do planetary climates respond to stellar evolution, e.g., sustaining early liquid water in spite of a faint young sun? (6) How important are the timescales of climate forcing and their dynamical drivers? Finally, we suggest crucial Mars measurements (unprioritized) to address these questions: (1) in situ petrology at multiple units/sites; (2) continued quantification of volatile reservoirs and new isotopic measurements of H, C, N, O, S, Cl, and noble gases in rocks that sample multiple stratigraphic sections; (3) radiometric age dating of units in stratigraphic sections and from key volcanic and impact units; (4) higher resolution measurements of heat flux, subsurface structure, and magnetic field anomalies coupled with absolute age dating. The unique dataset recording the evolution of early Mars will feed forward to understanding divergent evolutionary paths of the Earth, Venus, and thousands of small rocky extrasolar planets yet to be discovered. |
Septiembre de 2016
Acceleration of regional plate subduction beneath Kanto, Japan, after the 2011 Tohoku-oki earthquake
Authors: Naoki Uchida, Youichi Asano et al
Link: Click here
Abstract
Two oceanic plates (the Pacific (PA) and Philippine Sea (PH)) subduct beneath the land plate, and they forms deeper (PH-PA) and shallower (land-PH) plate boundaries beneath Kanto. Remarkably enhanced seismicity was observed in the densely populated area after the 2011 Tohoku-oki earthquake, which cannot |
simply be explained by the southern expansion of the postseismic slip of the earthquake. We examine interplate repeating earthquakes to constrain the relative plate motion across aseismically slipping faults. The repeater slip rates show creep rates in the deeper and shallower boundaries, respectively, increased to 2.4–6.6 times and 1.3–6.2 times the pre-Tohoku-oki rates. In addition, the repeater slip directions show no change larger than 4° in the deeper boundary. The interplate creep rates and slip directions suggest that regional movements of both the two plates had accelerated. They probably caused the seismicity increase, frequent slow slips on the shallower boundary, and enhanced probability of larger earthquakes. |
Septiembre de 2016
Slip distribution of the 2014 MW=8.1 Pisagua, northern Chile, earthquake sequence estimated from coseismic fore-arc surface cracks
Authors: John P. Loveless, Chelsea P. Scott et al
Link: Click here
Abstract
The 2014 MW?=?8.1 Iquique (Pisagua), Chile earthquake sequence ruptured a segment of the Nazca-South America subduction zone that last hosted a great earthquake in 1877. The sequence opened >3,700 surface cracks in the fore arc of decameter-scale length and millimeter-to centimeter-scale aperture. We use the strikes of |
coseismically applied tension, to estimate the slip distribution of the mainshock and largest aftershock. The slip estimates are compatible with those based on seismic, geodetic, and tsunami data, indicating that geologic observations can also place quantitative constraints on rupture properties. The earthquake sequence ruptured between two asperities inferred from a regional-scale distribution of surface cracks, interpreted to represent a modal or most common rupture scenario for the northern Chile subduction zone. We suggest that past events, including the 1877 earthquake, broke the 2014 Pisagua source area together with adjacent sections in a through-going rupture. |
Septiembre de 2016
Large earthquakes create vertical permeability by breaching aquitards
Authors: Chi-Yuen Wang, Xin Liao et al
Link: Click here
Abstract
Hydrologic responses to earthquakes and their mechanisms have been widely studied. Some responses have been attributed to increases in the vertical permeability. However, basic questions remain: How do increases in the vertical permeability occur? How frequently do they occur? Is there a quantitative measure for detecting the occurrence of aquitard breaching? We try to answer these questions by examining data from a dense network of ∼50 monitoring stations of clustered wells in a sedimentary basin near the epicenter of the 1999 M7.6 Chi-Chi earthquake in western Taiwan. While most stations show evidence that confined aquifers remained confined after the earthquake, about
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10% of the stations show evidence of coseismic breaching of aquitards, creating vertical permeability as high as that of aquifers. The water levels in wells without evidence of coseismic breaching of aquitards show tidal responses similar to that of a confined aquifer before and after the earthquake. Those wells with evidence of coseismic breaching of aquitards, on the other hand, show distinctly different postseismic tidal response. Furthermore, the postseismic tidal response of different aquifers became strikingly similar, suggesting that the aquifers became hydraulically connected and the connection was maintained many months thereafter. Breaching of aquitards by large earthquakes has significant implications for a number of societal issues such as the safety of water resources, the security of underground waste repositories, and the production of oil and gas. The method demonstrated here may be used for detecting the occurrence of aquitard breaching by large earthquakes in other seismically active areas. |
Septiembre de 2016
Validating induced seismicity forecast models—Induced Seismicity Test Bench
Authors: B. L. Ehlmann, F. S. Anderson et al
Link: Click here
Abstract
With the advent of exoplanetary astronomy and the ongoing discovery of terrestrial-type planets around other stars, our own solar system becomes a key testing ground for ideas about what factors control planetary evolution. In particular, what allows a planet to be both within a potentially habitable zone and sustain habitability over long geologic time, are crucial issues. In this regard, Mars is uniquely suited, providing the solar system's longest record of the interplay of the physical and chemical processes relevant to habitability on an accessible rocky planet with an atmosphere and hydrosphere. Here we review current understanding and update the timeline of key processes in early Mars history. We then draw on knowledge of exoplanets and the other solar system terrestrial planets to identify 6 broad questions of high importance to the development and sustaining of habitability (unprioritized): (1) Is small planetary size fatal? (2) How do magnetic
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fields influence atmospheric evolution? (3) To what extent does starting composition dictate subsequent evolution, including redox processes and the availability of water and organics? (4) Does early bombardment during an era of higher impact flux have a net deleterious or beneficial influence? (5) How do planetary climates respond to stellar evolution, e.g., sustaining early liquid water in spite of a faint young sun? (6) How important are the timescales of climate forcing and their dynamical drivers? Finally, we suggest crucial Mars measurements (unprioritized) to address these questions: (1) in situ petrology at multiple units/sites; (2) continued quantification of volatile reservoirs and new isotopic measurements of H, C, N, O, S, Cl, and noble gases in rocks that sample multiple stratigraphic sections; (3) radiometric age dating of units in stratigraphic sections and from key volcanic and impact units; (4) higher resolution measurements of heat flux, subsurface structure, and magnetic field anomalies coupled with absolute age dating. The unique dataset recording the evolution of early Mars will feed forward to understanding divergent evolutionary paths of the Earth, Venus, and thousands of small rocky extrasolar planets yet to be discovered. |
Septiembre de 2016
Theoretical limits on detection and analysis of small earthquakes
Authors: Grzegorz Kwiatek and Yehuda Ben-Zion
Link: Click here
We investigate theoretical limits on detection and reliable estimates of source characteristics of small earthquakes using synthetic seismograms for shear/tensile dislocations on kinematic circular ruptures and observed seismic noise and properties of several acquisition systems (instrument response, sampling rate). Simulated source time functions for shear/tensile dislocation events with different magnitudes, static stress drops, and rupture velocities provide estimates for the amplitude and frequency content of P and S
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phases at various observation angles. The source time functions are convolved with a Green's function for a homogenous solid assuming given P, S wave velocities and attenuation coefficients and a given instrument response. The synthetic waveforms are superposed with average levels of the observed ambient seismic noise up to 1 kHz. The combined seismograms are used to calculate signal-to-noise ratios and expected frequency content of P and S phases at various locations. The synthetic simulations of signal-to-noise ratio reproduce observed ratios extracted from several well-recorded data sets. The results provide guidelines on detection of small events in various geological environments, along with information relevant to reliable analyses of earthquake source properties. |
Septiembre de 2016
Novel determination of radon-222 velocity in deep subsurface rocks and the feasibility to using radon as an earthquake precursor
Authors: Hovav Zafrir, Yochai Ben Horin et al
Link: Click here
Abstract
A novel technique utilizing simultaneous radon monitoring by gamma and alpha detectors to differentiate between the radon climatic driving forces and others has been improved and used for deep subsurface investigation. Detailed long-term monitoring served as a proxy for studying
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radon movement within the shallow and deep subsurface, as well as for analyzing the effect of various parameters of the radon transport pattern. The main achievements of the investigation are (a) determination, for the first time, of the radon movement velocity within rock layers at depths of several tens of meters, namely, 25 m/h on average; (b) distinguishing between the diurnal periodical effect of the ambient temperature and the semidiurnal effect of the ambient pressure on the radon temporal spectrum; and (c) identification of a radon random preseismic anomaly preceding the Nuweiba, M 5.5 earthquake of 27 June 2015 that occurred within Dead Sea Fault Zone. |
Septiembre de 2016
Coseismic slip and early afterslip of the 2015 Illapel, Chile, earthquake: Implications for frictional heterogeneity and coastal uplift
Authors: William D. Barnhart, Jessica R. Murray et al
Link: Click here
Abstract
Great subduction earthquakes are thought to rupture portions of the megathrust, where interseismic coupling is high and velocity-weakening frictional behavior is dominant, releasing elastic deformation accrued over a seismic cycle. Conversely, postseismic afterslip is assumed to occur primarily in regions of velocity-strengthening frictional characteristics that may correlate with lower interseismic coupling. However, it remains unclear if fixed frictional properties of the subduction interface, coseismic or aftershock-induced stress redistribution, or other factors control the spatial distribution of afterslip. Here we use interferometric synthetic aperture radar and Global Position System observations to
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map the distribution of coseismic slip of the 2015 Mw 8.3 Illapel, Chile, earthquake and afterslip within the first 38 days following the earthquake. We find that afterslip overlaps the coseismic slip area and propagates along-strike into regions of both high and moderate interseismic coupling. The significance of these observations, however, is tempered by the limited resolution of geodetic inversions for both slip and coupling. Additional afterslip imaged deeper on the fault surface bounds a discrete region of deep coseismic slip, and both contribute to net uplift of the Chilean Coastal Cordillera. A simple partitioning of the subduction interface into regions of fixed frictional properties cannot reconcile our geodetic observations. Instead, stress heterogeneities, either preexisting or induced by the earthquake, likely provide the primary control on the afterslip distribution for this subduction zone earthquake. We also explore the occurrence of coseismic and postseismic coastal uplift in this sequence and its implications for recent hypotheses concerning the source of permanent coastal uplift along subduction zones. |
Septiembre de 2016
ITRF2014: A new release of the International Terrestrial Reference Frame modeling nonlinear station motions
Authors: Zuheir Altamimi, Paul Rebischung et al
Link: Click here
Abstract
For the first time in the International Terrestrial Reference Frame (ITRF) history, the ITRF2014 is generated with an enhanced modeling of nonlinear station motions, including seasonal (annual and semiannual) signals of station positions and postseismic deformation for sites that were subject to major earthquakes. Using the full observation history of the four space geodetic techniques (very long baseline interferometry (VLBI), satellite laser ranging (SLR), Global Navigation Satellite Systems (GNSS), and Doppler orbitography and radiopositioning integrated by satellite (DORIS)), the corresponding international services provided reprocessed time series (weekly from SLR and DORIS, daily from GNSS, and 24 h session-wise from VLBI) of station positions and daily Earth Orientation Parameters. ITRF2014 is demonstrated to be superior to past ITRF releases, as it precisely models the actual station trajectories leading to a more robust secular
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frame and site velocities. The ITRF2014 long-term origin coincides with the Earth system center of mass as sensed by SLR observations collected on the two LAGEOS satellites over the time span between 1993.0 and 2015.0. The estimated accuracy of the ITRF2014 origin, as reflected by the level of agreement with the ITRF2008 (both origins are defined by SLR), is at the level of less than 3 mm at epoch 2010.0 and less than 0.2 mm/yr in time evolution. The ITRF2014 scale is defined by the arithmetic average of the implicit scales of SLR and VLBI solutions as obtained by the stacking of their respective time series. The resulting scale and scale rate differences between the two solutions are 1.37 (±0.10) ppb at epoch 2010.0 and 0.02 (±0.02) ppb/yr. While the postseismic deformation models were estimated using GNSS/GPS data, the resulting parametric models at earthquake colocation sites were applied to the station position time series of the three other techniques, showing a very high level of consistency which enforces more the link between techniques within the ITRF2014 frame. The users should be aware that the postseismic deformation models are part of the ITRF2014 products, unlike the annual and semiannual signals, which were estimated internally with the only purpose of enhancing the velocity field estimation of the secular frame. |
Septiembre de 2016
Rapid re-inflation following the 2011-2012 rhyodacite eruption at Cordón Caulle volcano (Southern Andes) imaged by InSAR: evidence for magma reservoir refill
Authors: Francisco Delgado, Matthew Pritchard et al
Link: Click here
Abstract
Cordón Caulle is a large fissural volcano that has erupted rhyodacitic magma of the same composition in its past three historical eruptions in 1921, 1960 and 2011-2012. There was
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and during the 2011-2012 eruption – here we use C and X band InSAR time series results to document post-eruptive uplift up to 0.8?m between March 2012 and May 2015, with LOS rates up to 45?cm/yr that have been largely aseismic, along with subsidence in the 2011-2012 lava flow. The 2012 uplift rate is one of the largest for silicic systems, and was likely produced by the intrusion of ~0.125?km3 of magma in the same tectonically controlled plumbing system that has been active during the historical eruptions. Nevertheless the uplift ended before the reservoir refilled with the erupted volume, maybe due to a change in the pressure gradient produced by the 2011-2012 eruption. |
Septiembre de 2016
New perspectives on self-similarity for shallow thrust earthquakes
Authors: Marine A. Denolle and Peter M. Shearer et al
Link: Click here
Abstract
Scaling of dynamic rupture processes from small to large earthquakes is critical to seismic hazard assessment. Large subduction earthquakes are typically remote and we mostly rely on teleseismic body waves to extract information on their slip rate functions. We estimate the P-wave source spectra of 942 thrust earthquakes of magnitude M5.5 and above by carefully removing wave propagation effects (geometrical spreading, attenuation, and free surface effects). The conventional spectral model of a single corner frequency and high-frequency falloff rate does not explain our data
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and we instead introduce a double-corner-frequency model, modified from the Haskell propagating source model, with an intermediate falloff of f-1. The first corner frequency f1 relates closely to the source duration T1, its scaling follows inline image for MW<7.5 and changes to inline image for larger earthquakes. An elliptical rupture geometry better explains the observed scaling than circular crack models. The second time scale T2 varies more weakly with moment, inline image, varies weakly with depth, and can be interpreted either as expressions of starting and stopping phases, as a pulse-like rupture, or a dynamic weakening process. Estimated stress drops and scaled energy (ratio of radiated energy over seismic moment) are both invariant with seismic moment. However, the observed earthquakes are not self-similar because their source geometry and spectral shapes vary with earthquake size. We find and map global variations of these source parameters. |
Septiembre de 2016
How a complex basaltic volcanic system works: Constraints from integrating seismic, geodetic, and petrological data at Mount Etna volcano during the July–August 2014 eruption
Authors: Marco Viccaro, Francesco Zuccarello et al
Link: Click here
Abstract
Integrating geodetic, seismic, and petrological data for a recent eruptive episode at Mount Etna has enabled us to define the history of magma storage and transfer within the multilevel structure of the volcano, providing spatial and temporal constraints for magma movements before the eruption. Geodetic data related to the July–August 2014 activity provide evidence of a magma reservoir at ~4 km below sea level. This reservoir pressurized from late March 2014 and fed magmas that were then erupted from vents on the lower eastern flank of North-East Crater (NEC) and at New South-East Crater (NSEC) summit
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crater during the July eruptive activity. Magma drainage caused its depressurization since mid-July. Textural and microanalytical data obtained from plagioclase crystals indicate similar disequilibrium textures and compositions at the cores in lavas erupted at the base of NEC and NSEC, suggesting comparable deep histories of evolution and ascent. Conversely, the compositional differences observed at the crystal rims have been associated to distinct degassing styles during storage in a shallow magma reservoir. Seismic data have constrained depth for a shallow part of the plumbing system at 1–2 km above sea level. Timescales of magma storage and transfer have also been calculated through diffusion modeling of zoning in olivine crystals of the two systems. Our data reveal a common deep history of magmas from the two systems, which is consistent with a recharging phase by more mafic magma between late March and early June 2014. Later, the magma continued its crystallization under distinct chemical and physical conditions at shallower levels. |
Septiembre de 2016
An efficient repeating signal detector to investigate earthquake swarms
Authors: Robert J. Skoumal, Michael R. Brudzinski et al
Link: Click here
Abstract
Repetitive earthquake swarms have been recognized as key signatures in fluid injection induced seismicity, precursors to volcanic eruptions, and slow slip events preceding megathrust earthquakes. We investigate earthquake swarms by developing a Repeating Signal Detector (RSD), a computationally efficient algorithm utilizing agglomerative clustering to identify similar waveforms buried in years of seismic recordings using a single seismometer. Instead of relying on existing earthquake catalogs of larger earthquakes, RSD identifies characteristic repetitive waveforms by rapidly identifying signals of interest above a low signal-to-noise ratio and then grouping based on spectral and time domain characteristics,
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resulting in dramatically shorter processing time than more exhaustive autocorrelation approaches. We investigate seismicity in four regions using RSD: (1) volcanic seismicity at Mammoth Mountain, California, (2) subduction-related seismicity in Oaxaca, Mexico, (3) induced seismicity in Central Alberta, Canada, and (4) induced seismicity in Harrison County, Ohio. In each case, RSD detects a similar or larger number of earthquakes than existing catalogs created using more time intensive methods. In Harrison County, RSD identifies 18 seismic sequences that correlate temporally and spatially to separate hydraulic fracturing operations, 15 of which were previously unreported. RSD utilizes a single seismometer for earthquake detection which enables seismicity to be quickly identified in poorly instrumented regions at the expense of relying on another method to locate the new detections. Due to the smaller computation overhead and success at distances up to ~50 km, RSD is well suited for real-time detection of low-magnitude earthquake swarms with permanent regional networks. |
Septiembre de 2016
Geoelectric hazard maps for the continental United States
Authors: Jeffrey J. Love, Antti Pulkkinen et al
Link: Click here
Abstract
In support of a multi-agency project for assessing induction hazards, we present maps of extreme-value geoelectric amplitudes over about half of the continental United States. These maps are constructed using a parameterization of induction: estimates of Earth-surface impedance, obtained at discrete geographic sites from magnetotelluric survey data, are convolved with latitude-dependent statistical maps of extreme-value geomagnetic activity, obtained from decades of |
magnetic observatory data. Geoelectric amplitudes are estimated for geomagnetic waveforms having 240-s sinusoidal period and amplitudes over 10 minutes that exceed a once-per-century threshold. As a result of the combination of geographic differences in geomagnetic activity and Earth-surface impedance, once-per-century geoelectric amplitudes span more than two orders of magnitude and are an intricate function of location. For north-south induction, once-per-century geoelectric amplitudes across large parts of the United States have a median value of 0.26 V/km; for east-west geomagnetic variation the median value is 0.23 V/km. At some locations, once-per-century geoelectric amplitues exceed 3 V/km. |
Septiembre de 2016
On the Origin of Earth's Moon
Author: Amy C. Barr
Link: Click here
Abstract
The Giant Impact is currently accepted as the leading theory for the formation of Earth's Moon. Successful scenarios for lunar origin should be able to explain the chemical composition of the Moon (volatile content and stable isotope ratios), the Moon's initial thermal state, and the system's bulk physical and dynamical properties. Hydrocode simulations of the formation of the Moon have long been able to match the bulk
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properties, but recent, more detailed work on the evolution of the protolunar disk has yielded great insight into the origin of the Moon's chemistry, and its early thermal history. Here, I show that the community has constructed the elements of an end-to-end theory for lunar origin that matches the overwhelming majority of observational constraints. In spite of the great progress made in recent years, new samples of the Moon, clarification of processes in the impact-generated disk, and a broader exploration of impact parameter space could yield even more insights into this fundamental and uniquely challenging geophysical problem. |
Septiembre de 2016
Mars' atmosphere: the sister planet, our statistical twin
Authors: Wilbur Chen, Shaun Lovejoy et al
Link: Click here
Abstract
Satellite-based martian reanalyses have allowed unprecedented comparisons between our atmosphere and that of our sister planet, underlining various similarities and differences in their respective dynamics. Yet by focusing on large scale structures and deterministic mechanisms they have improved our understanding of the dynamics only over fairly narrow ranges of (near) planetary scales. However, the Reynolds numbers of the flows on
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both planets are larger than 1011 and dissipation only occurs at centimetric (Mars) or millimetric scales (Earth) so that over most of their scale ranges, the dynamics are fully turbulent. In this paper, we therefore examine the high level, statistical, turbulent laws for the temperature, horizontal wind and surface pressure, finding that Earth and Mars have virtually identical statistical exponents so that their statistics are very similar over wide ranges. Therefore, it would seem that with the exception of certain aspects of the largest scales (such as the role of dust in atmospheric heating on Mars, or of water in its various phases on Earth), that the nonlinear dynamics are very similar. We argue that this is a prediction of the classical laws of turbulence when extended to planetary scales, and that it supports our use of turbulent laws on both planetary atmospheres.
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Septiembre de 2016
Implications of RCP emissions on future PM2.5 air quality and direct radiative forcing over China
Authors: Ke Li, Hong Liao et al
Link: Click here
Abstract
Severe PM2.5 air pollution in China and the First Grand National Standard (FGNS), implemented in 2016 (annual PM2.5 concentration target of less than 35 µg m−3), necessitate urgent reduction strategies. This study applied the nested-grid version of the GEOS-Chem model to quantify 2000–2050 changes in PM2.5 air quality and related direct radiative forcing (DRF) in China, based on future emissions changes under the RCP scenarios of RCP2.6, RCP4.5, RCP6.0 and RCP8.5. In the near-term (2000–2030), a projected maximum increase in PM2.5 concentrations of 10–15 µg m−3 is found over east China under RCP6.0 and RCP8.5, and less than 5 µg m−3 under RCP2.6 and RCP4.5. In the long-term (2000–2050), PM2.5 pollution clearly improves, and the largest decrease in PM2.5 concentrations of 15–30 µg m−3 is over east China under all RCPs except RCP6.0. Focusing particularly on highly polluted regions, we find that Beijing–Tianjin–Hebei (BTH) wintertime PM2.5
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concentrations meeting the FGNS occur after 2040 under RCP2.6, RCP4.5, and RCP8.5, and summertime PM2.5 concentrations reach this goal by 2030 under RCP2.6 and RCP4.5. In Sichuan Basin (SCB), wintertime PM2.5 concentrations below the FGNS occur only in 2050 under RCP2.6 and RCP4.5, although future summertime PM2.5 will be well controlled. The difficulty in controlling future PM2.5 concentrations relates to unmitigated high levels of nitrate, although NOx and SO2 emissions show substantial reductions during 2020–2040. The changes in aerosol concentrations lead to positive aerosol DRF over east China (20°–45°N, 100°–125°E) by 1.22, 1.88, and 0.66 W m−2 in 2050 relative to 2000 under RCP2.6, RCP4.5, and RCP8.5, respectively. When considering both health and climate effects of PM2.5 over China, for example, PM2.5 concentrations averaged over east China under RCP4.5 (RCP2.6) decrease by 54% (43%) in 2050 relative to 2000, but at the cost of warming with DRF of 1.88 (1.22) W m−2. Our results indicate that it will be possible to mitigate future PM2.5 pollution in China, but it will likely take two decades for polluted regions such as BTH and SCB to meet the FGNS, based on all RCP scenarios. At the same time, the consequent warming effects reduced aerosols are also significant and inevitable. |
Septiembre de 2016
An Investigation on How Inner-Core Structures Obtained through Radar Data Assimilation Affect Track Forecasting of Typhoon Jangmi (2008) near Taiwan Island
Authors: Mingjun Wang, Ming Xue et al
Link: Click here
Abstract
The impacts of radar data assimilation (DA) on the westward track deflection of Typhoon Jangmi (2008) near Taiwan Island and the deflection mechanism are investigated. Initial conditions from two data assimilation experiments with significant track forecast differences are analyzed and compared. The environmental, axisymmetric, wavenumber 1 to 3 asymmetric fields of the typhoon are decomposed using vortex separation and Fourier decomposition methods. The components are selectively recomposed into new initial conditions that include different vortex-scale components to examine the impact of individual
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components on the track prediction. The wavenumber 1 asymmetric structure is found to play a dominant role in the westward deflection of Typhoon Jangmi, and the accurate analysis of this component with radar DA helps to improve the track forecast. The wavenumber 1 asymmetric circulation is manifested as a pair of cyclonic and anticyclonic gyres with well-defined ventilation flows through the inner-core region, which provides additional steering of the typhoon vortex. The layer-mean environmental steering flow and ventilation flow associated with the wavenumber 1 gyres are further calculated to quantitatively evaluate the impact of ventilation flow. The ventilation flow is shown to be responsible for most of the westward motion component, suggesting again its role in causing the westward track deflection of typhoon Jangmi. The results also suggest the importance of analyzing vortex-scale asymmetric structures for accurate tropical cyclone track forecasting, especially when there is a significant track deflection. |
Septiembre de 2016
Ocean worlds in the outer solar system
Authors: F. Nimmo and R. T. Pappalardo
Link: Click here
Abstract
Many outer solar system bodies are thought to harbor liquid water oceans beneath their ice
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shells. This article first reviews how such oceans are detected. We then discuss how they are maintained, when they formed, and what the oceans' likely characteristics are. We focus in particular on Europa, Ganymede, Callisto, Titan, and Enceladus, bodies for which there is direct evidence of subsurface oceans. We also consider candidate ocean worlds such as Pluto and Triton. |
Septiembre de 2016
How a complex basaltic volcanic system works: Constraints from integrating seismic, geodetic, and petrological data at Mount Etna volcano during the July–August 2014 eruption
Authors:Marco Viccaro, Francesco Zuccarello et al
Link: Click here
Abstract
Integrating geodetic, seismic, and petrological data for a recent eruptive episode at Mount Etna has enabled us to define the history of magma storage and transfer within the multilevel structure of the volcano, providing spatial and temporal constraints for magma movements before the eruption. Geodetic data related to the July– August 2014 activity provide evidence of a magma reservoir at ~4 km below sea level. This reservoir pressurized from late March 2014 and fed magmas that were then erupted from vents on the lower eastern flank of North-East Crater (NEC) and at New South-East Crater (NSEC) summit
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crater during the July eruptive activity. Magma drainage caused its depressurization since mid-July. Textural and microanalytical data obtained from plagioclase crystals indicate similar disequilibrium textures and compositions at the cores in lavas erupted at the base of NEC and NSEC, suggesting comparable deep histories of evolution and ascent. Conversely, the compositional differences observed at the crystal rims have been associated to distinct degassing styles during storage in a shallow magma reservoir. Seismic data have constrained depth for a shallow part of the plumbing system at 1–2 km above sea level. Timescales of magma storage and transfer have also been calculated through diffusion modeling of zoning in olivine crystals of the two systems. Our data reveal a common deep history of magmas from the two systems, which is consistent with a recharging phase by more mafic magma between late March and early June 2014. Later, the magma continued its crystallization under distinct chemical and physical conditions at shallower levels. |
Septiembre de 2016
Correlation analysis for preseismic total electron content anomalies around the 2011 Tohoku-Oki earthquake
Authors: Takuya Iwata and Ken Umeno
Link: Click here
Abstract
We can observe the changes of Total Electron Content, TEC, in ionosphere by analyzing the data from Global Navigation Satellite Systems (GNSS) satellites. Up to now, preseismic TEC anomalies have been reported in several papers. However, they are not so clear as coseismic TEC anomalies, and their analysis methods have some problems for practical earthquake prediction. One factor making it difficult to detect TEC anomalies is large noises in TEC data. Nonnegligible TEC disturbances are caused by many natural mechanisms. To overcome this difficulty, we propose correlation analyses
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between one GNSS station and GNSS stations surrounding it. First, we model TEC time series over a few hours using polynomial functions of time. Second, we calculate prediction errors as the departure of the TEC time series from the models over time scale of a few minutes and define it as the TEC anomaly. Third, we calculate the correlation between anomaly of one GNSS station and those at the surrounding stations. Although such a correlation method has long been used for radio communications, in particular for spread spectrum communications and very long baseline interferometry to increase signal-to-noise ratio, it has not been widely applied for TEC analysis. As a result of our method, we demonstrate that the correlation analysis can detect preseismic anomalies about 1 h before the 2011 Tohoku-Oki earthquake on 11 March (Mw 9.0), 20 min before the foreshock on 9 March and 40 min before the aftershock on 7 April (Mw 7.3). |
Septiembre de 2016
Apparent triggering function of aftershocks resulting from rate-dependent incompleteness of earthquake catalogs
Author: Sebastian Hainzl
Link: Click here
Abstract
The onset of the aftershock decay after main shocks is controversial. Physical models predict that the onset time is stress dependent, and catalog analysis shows a clear increase of the c value of the Omori-Utsu law with increasing main shock magnitude. However, earthquake catalogs are known to have variable quality and completeness levels; in particular, they miss events directly after main shocks. Thus, it has been also argued that the delayed onset of recorded aftershock activity triggered by large
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earthquakes is simply an artifact of the time-varying completeness. Here I utilize a recent approach describing the detection probability of earthquakes as function of the actual earthquake rate. I derive an analytical relation between apparent and true earthquake rate which only depends on the blind time of detection algorithms after the occurrence of an earthquake. This relation is tested and verified for synthetic simulations of Omori-type aftershock sequences. For a comparison, I analyze earthquake sequences occurred in Southern California and Taiwan, finding that the derived analytical decay function consistently explains the empirical aftershock activity in the catalogs. This indicates that the observed scaling of the Omori c value is mainly related to catalog incompleteness and not to any underlying physical process. |
Septiembre de 2016
Mantle convection models constrain central Neo-Tethys Ocean reconstructions
Authors:Rainer Nerlich, Lorenzo Colli et al.
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Abstract
A striking feature of the Indian Ocean is a distinct geoid low south of India, pointing to a regionally anomalous mantle density structure. Equally prominent are rapid plate convergence rate variations between India and SE Asia, particularly in Late Cretaceous/Paleocene times. Both observations are linked to the central Neo-Tethys Ocean subduction history, for which competing scenarios have been proposed. Here we evaluate
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three alternative reconstructions by assimilating their associated time-dependent velocity fields in global high-resolution geodynamic Earth models, allowing us to predict the resulting seismic mantle heterogeneity and geoid signal. Our analysis reveals that a geoid low similar to the one observed develops naturally when a long-lived back-arc basin south of Eurasia's paleo-margin is assumed. A quantitative comparison to seismic tomography further supports this model. In contrast, reconstructions assuming a single northward dipping subduction zone along Eurasia's margin or models incorporating a temporary southward dipping intra-oceanic subduction zone cannot sufficiently reproduce geoid and seismic observations. |
Septiembre de 2016
Variations of ionospheric plasma at different altitudes before the 2005 Sumatra Indonesia Ms7.2 earthquake
Authors: Jing Liu, Xuemin Zhang et al.
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Abstract
Resent years, many researchers pay more attention to abnormities before earthquake, and in this study, seismo-ionospheric synchronous disturbances at different altitudes by GPS and satellite observations were firstly studied around one Sumatra Indonesia Ms 7.2 earthquake occurred on July 5 2005. By using the same temporal and spatial methods, data of GPS-TEC from JPL, electron density (Ne) from DEMETER and ion density (Ni) from DMSP were deeply |
analyzed. The ionospheric plasma disturbances in GPS-TEC and increasement of Ne at 710 km were found on July 4, and plasma density at the three altitudes has all increased on July 7 after the earthquake. All the disturbances were not just above the epicenter. TEC perturbations have happened at the east of the epicenter for the two days, and electron density enhancement at 710 km has moved to west of the TEC perturbations at the same time on July 4, which may be caused by E × B drift. The moving direction of up-going plasma was simulated using SAMI2 model. The results have shown that the plasma will move to higher altitude along the geomagnetic force line, which could exactly account for the plasma density enhancement in the northern direction of the geomagnetic south latitude earthquake. |
Septiembre de 2016
The forced precession of the Moon's inner core
Authors: Mathieu Dumberry, Mark A. Wieczorek et al.
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Abstract
The tilt angle of the 18.6 year precession of the Moon's solid inner core is unknown, but it is set by a balance between gravitational and pressure torques acting on its elliptical figure. We show here that to first order, the angle of precession of the inner core of a planetary body is determined by the frequency of the free inner core nutation, ωficn, relative to the precession frequency, Ωp. If |ωficn|≪|Ωp|, the inner core is blind to the gravitational influence of the mantle. If |ωficn|≫|Ωp|, the inner core is gravitationally |
locked to the mantle and is nearly aligned with it. If ωficn≈Ωp, large inner core tilt angles can result from resonant excitation. Viscous inner core relaxation and electromagnetic coupling can attenuate large tilt angles. For the specific case of the Moon, we show that ωficn is to within a factor of 2 of Ωp = 2π/18.6 yr−1. For a rigid inner core, this implies a tilt of 2 to 5° with respect to the mantle, and larger if ωficn is very close to Ωp. More modest tilt angles between 0 and 0.5° result if viscous relaxation within the inner core occurs on a timescale of one lunar day. Predictions from our model may be used in an attempt to detect the gravity signal resulting from a tilted inner core, to determine the past history of the inner core tilt angle, and to assess models of dynamo generation powered by differential rotation at the core-mantle and inner core boundaries. |
Agosto de 2016
Highly siderophile elements were stripped from Earth’s mantle by iron sulfide segregation
Authors: David C. Rubie, Vera Laurenz et al
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Abstract
Highly siderophile elements (HSEs) are strongly depleted in the bulk silicate Earth (BSE) but are present in near-chondritic relative abundances. The conventional explanation is that the HSEs were stripped from the mantle by the segregation of metal during core formation but were added
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back in near-chondritic proportions by late accretion, after core formation had ceased. Here we show that metal-silicate equilibration and segregation during Earth’s core formation actually increased HSE mantle concentrations because HSE partition coefficients are relatively low at the high pressures of core formation within Earth. The pervasive exsolution and segregation of iron sulfide liquid from silicate liquid (the “Hadean matte”) stripped magma oceans of HSEs during cooling and crystallization, before late accretion, and resulted in slightly suprachondritic palladium/iridium and ruthenium/iridium ratios. |
Agosto de 2016
Local near instantaneously dynamically triggered aftershocks of large earthquakes
Authors: Wenyuan Fan and Peter M. Shearer et al
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Abstract
Aftershocks are often triggered by static- and/or dynamic-stress changes caused by mainshocks. The relative importance of the two triggering mechanisms is controversial at near-to-intermediate distances. We detected and located 48 previously unidentified large early aftershocks triggered by earthquakes with magnitudes
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between ≥7 and 8 within a few fault lengths (approximately 300 kilometers), during times that high-amplitude surface waves arrive from the mainshock (less than 200 seconds). The observations indicate that near-to-intermediate-field dynamic triggering commonly exists and fundamentally promotes aftershock occurrence. The mainshocks and their nearby early aftershocks are located at major subduction zones and continental boundaries, and mainshocks with all types of faulting-mechanisms (normal, reverse, and strike-slip) can trigger early aftershocks. |
Agosto de 2016
On the Possibility of Viscoelastic Deformation of the Large South Polar Craters and True Polar Wander on the Asteroid Vesta
Authors: Saman Karimi and Andrew J. Dombard et al
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Abstract
The asteroid Vesta, located within the inner asteroid belt, is a differentiated body with a prominent rotational bulge. NASA's Dawn mission revealed the presence of two large, relatively shallow impact craters in the south polar region, one with a high standing central peak. The shallowness and prominent central peak are reminiscent of large craters on some icy satellites that may have experienced strong topographic
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relaxation. The location of these basins near the south pole is also unusual and suggests true polar wander, which requires relaxation of the rotational bulge. Thus, we use the finite element method and a viscoelastic rheology to examine the feasibility of relaxation processes operating on Vesta. Given the plausible thermal state of Vesta by the decay of long-lived radioactive elements, we find that the lithosphere is not compliant enough to allow strong relaxation of the large south polar craters, and thus the peculiar morphology is possibly a product of the formation of these large basins at a planetary scale. Additionally, the asteroid has not been warm enough to permit the relaxation of the rotational bulge. Consequently, these craters both happened to form near the south pole, as unlikely as that is. |
Agosto de 2016
Unifying catchment water balance models for different time scales through the maximum entropy production principle
Authors: Jianshi Zhao, Dingbao Wang et al
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Abstract
The paper presents a thermodynamic basis for water balance partitioning at the catchment scale, through formulation of flux-force relationships for the constituent hydrological processes, leading to the derivation of optimality conditions that satisfy the principle of Maximum Entropy Production
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(MEP). Application of these optimality principles at three different time scales leads to the derivation of water balance equations that mimic widely used, empirical models, i.e., Budyko-type model over long-term scale, the “abcd” model at monthly scale, and the SCS model at the event scale. The applicability of MEP in each case helps to draw connections between the water balances at the three different time scales, and to demonstrate a common thermodynamic basis for the otherwise empirical water balance models. In particular, it is concluded that the long time scale Budyko-type model and the event scale SCS model are both special cases of the monthly “abcd” model. |
Agosto de 2016
Apparent triggering function of aftershocks resulting from rate-dependent incompleteness of earthquake catalogs
Author: Sebastian Hainzl.
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Abstract
The onset of the aftershock decay after mainshocks is controversial. Physical models predict that the onset time is stress-dependent and catalog analysis shows a clear increase of the c-value of the Omori-Utsu law with increasing mainshock magnitude. However, earthquake catalogs are known to have variable quality and completeness levels; in particular, they miss events directly after mainshocks. Thus it has been also argued that the delayed onset of recorded aftershock activity triggered by large earthquakes
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is simply an artifact of the time-varying completeness. Here I utilize a recent approach describing the detection probability of earthquakes as function of the actual earthquake rate. I derive an analytical relation between apparent and true earthquake rate which only depends on the blind time of detection algorithms after the occurrence of an earthquake. This relation is tested and verified for synthetic simulations of Omori-type aftershock sequences. For a comparison, I analyze earthquake sequences occurred in southern California and Taiwan, finding that the derived analytical decay function consistently explains the empirical aftershock activity in the catalogs. This indicates that the observed scaling of the
Omori c-value is mainly related to catalog incompleteness and not to any underlying physical process. |
Agosto de 2016
Modeling tsunami observations to evaluate a proposed late tsunami earthquake stage for the 16 September 2015 Illapel, Chile, Mw 8.3
Authors: Thorne Lay, Linyan Li et al.
Link: Click here
Abstract
Resolving seaward extent of slip during great subduction zone interplate ruptures using land-based seismological and geodetic observations
is challenging. Modeling of tsunami recordings from ocean-bottom pressure sensors of the Deep-ocean Assessment and Reporting of Tsunami (DART) network has added valuable constraints on near-trench slip for recent events.
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We use DART and tide gauge recordings to evaluate a proposed seismological scenario involving a late Mw 8.08 tsunami earthquake following the ~95 s long main rupture stage of the 16 September 2015 Illapel, Chile, Mw 8.3 earthquake. Tsunami observations constrain the spatial extent of any late tsunami earthquake slip to locate north of the main shock hypocenter. The proposed late shallow slip predicts tsunami signals with considerable amplitudes but shorter wavelengths compared to those of the main stage slip constrained by joint seismic and tsunami modeling, yielding overprediction of first-arrival amplitudes at DART and tide gauge stations when the two stages are combined. |
Agosto de 2016
Three-dimensional electrical resistivity model of the hydrothermal system in Long Valley Caldera, California, from magnetotellurics
Authors: J. R. Peacock, M. T. Mangan et al.
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Abstract
Though shallow flow of hydrothermal fluids in Long Valley Caldera, California, has been well studied, neither the hydrothermal source reservoir nor heat source has been well characterized. Here a grid of magnetotelluric data were collected around the Long Valley volcanic system and
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modeled in 3-D. The preferred electrical resistivity model suggests that the source reservoir is a narrow east-west elongated body 4 km below the west moat. The heat source could be a zone of 2–5% partial melt 8 km below Deer Mountain. Additionally, a collection of hypersaline fluids, not connected to the shallow hydrothermal system, is found 3 km below the medial graben, which could originate from a zone of 5–10% partial melt 8 km below the south moat. Below Mammoth Mountain is a 3 km thick isolated body containing fluids and gases originating from an 8 km deep zone of 5–10% basaltic partial melt. |
Agosto de 2016
An integrated analysis of the March 2015 Atacama floods
Authors: Andrew C. Wilcox, Cristian Escauriaza et al.
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Abstract
In March 2015 unusual ocean and atmospheric conditions produced many years' worth of rainfall in a ~48 h period over northern Chile's
Atacama Desert, one of Earth's driest regions, resulting in catastrophic flooding. Here we describe the hydrologic and geomorphic drivers of and responses to the 2015 Atacama floods. In the
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Salado River, we estimated a flood peak discharge of approximately 1000 m3/s, which caused widespread damage and high sediment loads that were primarily derived from valley-fill erosion; hillslopes remained surprisingly intact
despite their lack of vegetation. In the coastal city of Chañaral, flooding of the Salado River produced maximum water depths over 4.5 m, meters thick mud deposition in buildings and along city streets, and coastal erosion. The Atacama flooding has broad implications in the context of hazard reduction, erosion of contaminated legacy mine tailings, and the Atacama's status as a terrestrial analog for Mars. |
Agosto de 2016
Large ionospheric disturbances produced by the HAARP HF facility
Authors: Paul A. Bernhardt, Carl L. Siefring et al.
Link: Click here
Abstract
The enormous transmitter power, fully programmable antenna array, and agile frequency generation of the High Frequency Active Auroral Research Program (HAARP) facility in Alaska have allowed the production of unprecedented disturbances in the ionosphere. Using both pencil beams and conical (or twisted) beam transmissions, artificial ionization clouds have been generated near the second, third, fourth, and sixth harmonics of the electron gyrofrequency. The conical beam has been used to sustain these
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clouds for up to 5 h as opposed to less than 30 min durations produced using pencil beams. The largest density plasma clouds have been produced at the highest harmonic transmissions. Satellite radio transmissions at 253 MHz from the National Research Laboratory TACSat4 communications experiment have been severely disturbed by propagating through artificial plasma regions. The scintillation levels for UHF waves passing through artificial ionization clouds from HAARP are typically 16 dB. This is much larger than previously reported scintillations at other HF facilities which have been limited to 3 dB or less. The goals of future HAARP experiments should be to build on these discoveries to sustain plasma densities larger than that of the background ionosphere for use as ionospheric reflectors of radio signals. |
Agosto de 2016
The effects of dynamics on the triboelectrification of volcanic ash
Authors: Joshua Méndez Harper and Josef Dufek
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Abstract
Lightning is often observed during explosive volcanic eruptions, and the charging processes associated with these displays have been attributed to several mechanisms. In this work we delineate a set of experiments designed to quantify silicate-based triboelectric charging in the volcanic context. Using natural samples from three different volcanoes, we show that the rate of
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triboelectrification in a fluidized bed depends on the energy input into the granular system. Experiments are conducted employing nonintrusive electrostatic sensors, ensuring that all charge exchange arises solely from particle-particle collisions. At higher fluidization energies, particles undergo more frequent and energetic collisions, facilitating the transfer of charge. This finding implies that triboelectric charging could help promote charging in regions of the eruptive system that contain numerous particle-particle collisions such as the conduit and gas thrust regions. Our experiments also suggest that surface charge density is capped, at least in part, by atmospheric conditions, specifically the breakdown characteristics of the gas. |
Agosto de 2016
Theoretical limits on detection and analysis of small earthquakes
Authors: Grzegorz Kwiatek, Yehuda Ben-Zion et al
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Abstract
We investigate theoretical limits on detection and reliable estimates of source characteristics of small earthquakes using synthetic seismograms for shear/tensile dislocations on kinematic circular ruptures and observed seismic noise and properties of several acquisition systems (instrument response, sampling rate). Simulated source time functions for shear/tensile dislocation events with different magnitudes, static stress drops, and rupture velocities provide estimates for
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the amplitude and frequency content of P and S phases at various observation angles. The source time functions are convolved with a Green's function for a homogenous solid assuming given P, S wave velocities and attenuation coefficients and a given instrument response. The synthetic waveforms are superposed with average levels of the observed ambient seismic noise up to 1 kHz. The combined seismograms are used to calculate signal-to-noise ratios and expected frequency content of P and S phases at various locations. The synthetic simulations of signal-to-noise ratio reproduce observed ratios extracted from several well-recorded data sets. The results provide guidelines on detection of small events in various geological environments, along with information relevant to reliable analyses of earthquake source properties. |
Agosto de 2016
Conceptualizing socio-hydrological drought processes: The case of the Maya collapse
Authors: Linda Kull, Gemma Carr et al
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Abstract
With population growth, increasing water demands and climate change the need to understand the current and future pathways to water security is becoming more pressing. To contribute to addressing this challenge, we examine the link between water stress and society through socio-hydrological modeling. We conceptualize the interactions between an agricultural society with its environment in a |
stylized way. We apply the model to the case of the ancient Maya, a population that experienced a peak during the Classic Period (AD 600–830) and then declined during the ninth century. The hypothesis that modest drought periods played a major role in the society's collapse is explored. Simulating plausible feedbacks between water and society we show that a modest reduction in rainfall may lead to an 80% population collapse. Population density and crop sensitivity to droughts, however, may play an equally important role. The simulations indicate that construction of reservoirs results in less frequent drought impacts, but if the reservoirs run dry, drought impact may be more severe and the population drop may be larger. |
Agosto de 2016
Correlation Analysis for Pre-seismic Total Electron Content Anomalies around the 2011 Tohoku-Oki Earthquake
Authors: Takuya Iwata and Ken Umeno
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Abstract
We can observe the changes of Total Electron Content, TEC, in ionosphere by analyzing the data from GNSS satellites. Up to now, preseismic TEC anomalies have been reported in several papers. However, they are not so clear as coseismic TEC anomalies, and their analysis methods have some problems for practical earthquake prediction. One factor making it difficult to detect TEC anomalies is large noises in TEC data. Non-negligible TEC disturbances are caused by many natural mechanisms. To overcome this difficulty, we propose correlation analyses between one GNSS station and GNSS stations surrounding it. |
First, we model TEC time series over a few hours using polynomial functions of time. Second, we calculate prediction errors as the departure of the TEC time series from the models over time scale of a few minutes, and define it as the TEC anomaly. Third, we calculate the correlation between anomaly of one GNSS station and those at the surrounding stations. Although such a correlation method has long been used for radio communications, in particular for spread spectrum communications and very long baseline interferometry (VLBI) to increase SNR (signal to noise ratio), it has not been widely applied for TEC analysis. As a result of our method, we demonstrate that the correlation analysis can detect pre-seismic anomalies about one hour before the 2011 Tohoku-oki earthquake on March 11 (Mw 9.0), 20 minutes before the foreshock on March 9 and 40 minutes before the aftershock on April 7 (Mw 7.3). |
Agosto de 2016
The effects of dynamics on the triboelectrification of volcanic ash
Authors:
William D. Barnhart, Jessica R. Murray et al
Link: Click here
Abstract
Great subduction earthquakes are thought to rupture portions of the megathrust, where interseismic coupling is high and velocity-weakening frictional behavior is dominant, releasing elastic deformation accrued over a seismic cycle. Conversely, postseismic afterslip is assumed to occur primarily in regions of velocity-strengthening frictional characteristics that may correlate with lower interseismic coupling. However, it remains unclear if fixed frictional properties of the subduction interface, coseismic or aftershock-induced stress redistribution, or other factors control the spatial distribution of afterslip. Here we use interferometric synthetic aperture radar and Global Position System observations to map the
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distribution of coseismic slip of the 2015 Mw 8.3 Illapel, Chile, earthquake and afterslip within the first 38 days following the earthquake. We find that afterslip overlaps the coseismic slip area and propagates along-strike into regions of both high and moderate interseismic coupling. The significance of these observations, however, is tempered by the limited resolution of geodetic inversions for both slip and coupling. Additional afterslip imaged deeper on the fault surface bounds a discrete region of deep coseismic slip, and both contribute to net uplift of the Chilean Coastal Cordillera. A simple partitioning of the subduction interface into regions of fixed frictional properties cannot reconcile our geodetic observations. Instead, stress heterogeneities, either preexisting or induced by the earthquake, likely provide the primary control on the afterslip distribution for this subduction zone earthquake. We also explore the occurrence of coseismic and postseismic coastal uplift in this sequence and its implications for recent hypotheses concerning the source of permanent coastal uplift along subduction zones. |
Agosto de 2016
Coseismic slip and early afterslip of the 2015 Illapel, Chile, earthquake: Implications for frictional heterogeneity and coastal uplift
Authors: William D. Barnhart, Jessica R. Murray et al
Link: Click here
Abstract
Great subduction earthquakes are thought to rupture portions of the megathrust, where interseismic coupling is high and velocity-weakening frictional behavior is dominant, releasing elastic deformation accrued over a seismic cycle. Conversely, postseismic afterslip is assumed to occur primarily in regions of velocity-strengthening frictional characteristics that may correlate with lower interseismic coupling. However, it remains unclear if fixed frictional properties of the subduction interface, coseismic or aftershock-induced stress redistribution, or other factors control the spatial distribution of afterslip. Here we use interferometric synthetic aperture radar and
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Global Position System observations to map the distribution of coseismic slip of the 2015 Mw 8.3 Illapel, Chile, earthquake and afterslip within the first 38?days following the earthquake. We find that afterslip overlaps the coseismic slip area and propagates along-strike into regions of both high and moderate interseismic coupling. The significance of these observations, however, is tempered by the limited resolution of geodetic inversions for both slip and coupling. Additional afterslip imaged deeper on the fault surface bounds a discrete region of deep coseismic slip, and both contribute to net uplift of the Chilean Coastal Cordillera. A simple partitioning of the subduction interface into regions of fixed frictional properties cannot reconcile our geodetic observations. Instead, stress heterogeneities, either preexisting or induced by the earthquake, likely provide the primary control on the afterslip distribution for this subduction zone earthquake. We also explore the occurrence of coseismic and postseismic coastal uplift in this sequence and its implications for recent hypotheses concerning the source of permanent coastal uplift along subduction zones. |
Agosto de 2016
Extraordinary sediment delivery and rapid geomorphic response following the 2008–2009 eruption of Chaitén Volcano, Chile
Authors: Jon J. Major, Daniel Bertin et al.
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Abstract
The 10 day explosive phase of the 2008–2009 eruption of Chaitén volcano, Chile, draped adjacent watersheds with a few cm to >1 m of tephra. Subsequent lava-dome collapses generated pyroclastic flows that delivered additional sediment. During the waning phase of explosive activity, modest rainfall triggered an extraordinary sediment flush which swiftly aggraded multiple channels by many meters. Ten kilometer from the volcano, Chaitén River channel aggraded 7 m and the river avulsed through a coastal town. That aggradation and delta growth below the abandoned and avulsed channels allow estimates of postdisturbance traction-load
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transport rate. On the basis of preeruption bathymetry and remotely sensed measurements of delta-surface growth, we derived a time series of delta volume. The initial flush from 11 to 14 May 2008 deposited 0.5–1.5 × 106 m3 of sediment at the mouth of Chaitén River. By 26 May, after channel avulsion, a second delta amassed about 2 × 106 m3 of sediment; by late 2011 it amassed about 11 × 106 m3. Accumulated sediment consists of low-density vesicular pumice and lithic rhyolite sand. Rates of channel aggradation and delta growth, channel width, and an assumed deposit bulk density of 1100–1500 kg m−3 indicate mean traction-load transport rate just before and shortly after avulsion (∼14–15 May) was very high, possibly as great as several tens of kg s−1 m−1. From October 2008 to December 2011, mean traction-load transport rate declined from about 7 to 0.4 kg−1 m−1. Despite extraordinary sediment delivery, disturbed channels recovered rapidly (a few years). |
Agosto de 2016
Artificial periodic irregularities in the high-latitude ionosphere excited by the HAARP facility
Authors: N. V. Bakhmetieva, S. M. Grach et al.
Link: Click here
Abstract
We present results of the new observations of artificial periodic irregularities (APIs) in the ionosphere using the High Frequency Active Auroral Research Program (HAARP) heating facility carried out in late May and early June
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2014.The objective of this work is to detect API using high-latitude facility and analyze possible differences of the temporal and spatial variations of the API echoes in the high (HAARP) and middle (Sura) latitudes. Irregularities were created by the powerful wave of X mode and were sounded using the short probing pulses signals of X mode. API echoes were observed in the D, E, and F regions of the ionosphere. Amplitudes and characteristic times of the API echoes were measured. The API growth and decay times at HAARP (high latitudes) observed were similar to those at the Sura heating facility (midlatitudes). |
Agosto de 2016
Was Venus the First Habitable World of our Solar System?
Authors: M. J. Way, Anthony D. Del Genio et al.
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Abstract
Present-day Venus is an inhospitable place with surface temperatures approaching 750 K and an atmosphere 90 times as thick as Earth's. Billions of years ago the picture may have been very different. We have created a suite of 3-D climate simulations using topographic data from the Magellan mission, solar spectral irradiance
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estimates for 2.9 and 0.715 Gya, present-day Venus orbital parameters, an ocean volume consistent with current theory, and an atmospheric composition estimated for early Venus. Using these parameters we find that such a world could have had moderate temperatures if Venus had a rotation period slower than ~16 Earth days, despite an incident solar flux 46 − 70% higher than Earth receives. At its current rotation period, Venus's climate could have remained habitable until at least 715 million years ago. These results demonstrate the role rotation and topography play in understanding the climatic history of Venus-like exoplanets discovered in the present epoch. |
Agosto de 2016
Three-dimensional distribution of ionospheric anomalies prior to three large earthquakes in Chile
Authors: Liming He and Kosuke Heki
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Abstract
Using regional Global Positioning System (GPS) networks, we studied three-dimensional spatial structure of ionospheric total electron content (TEC) anomalies preceding three recent large earthquakes in Chile, South America, i.e., the 2010 Maule (Mw 8.8), the 2014 Iquique (Mw 8.2),
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and the 2015 Illapel (Mw 8.3) earthquakes. Both positive and negative TEC anomalies, with areal extent dependent on the earthquake magnitudes, appeared simultaneously 20–40 min before the earthquakes. For the two midlatitude earthquakes (2010 Maule and 2015 Illapel), positive anomalies occurred to the north of the epicenters at altitudes 150–250 km. The negative anomalies occurred farther to the north at higher altitudes 200–500 km. This lets the epicenter, the positive and negative anomalies align parallel with the local geomagnetic field, which is a typical structure of ionospheric anomalies occurring in response to positive surface electric charges. |
Agosto de 2016
Asteroid bombardment and the core of Theia as possible sources for the Earth's late veneer component
Author: Norman H. Sleep
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Abstract
The silicate Earth contains Pt-group elements in roughly chondritic relative ratios, but with absolute concentrations <1% chondrite. This veneer implies addition of chondrite-like material with 0.3–0.7% mass of the Earth's mantle or an equivalent planet-wide thickness of 5–20 km. The veneer thickness, 200–300 m, within the lunar crust and mantle is much less. One hypothesis is that the terrestrial veneer arrived after the moon-forming impact within a few large asteroids that happened to miss the smaller Moon. Alternatively, most of terrestrial veneer came from the core of the moon-forming impactor, Theia. The Moon then
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likely contains iron from Theia's core. Mass balances lend plausibility. The lunar core mass is ∼1.6 × 1021 kg and the excess FeO component in the lunar mantle is 1.3–3.5 × 1021 kg as Fe, totaling 3–5 × 1021 kg or a few percent of Theia's core. This mass is comparable to the excess Fe of 2.3–10 × 1021 kg in the Earth's mantle inferred from the veneer component. Chemically in this hypothesis, Fe metal from Theia's core entered the Moon-forming disk. H2O and Fe2O3 in the disk oxidized part of the Fe, leaving the lunar mantle near a Fe-FeO buffer. The remaining iron metal condensed, gathered Pt-group elements eventually into the lunar core. The silicate Moon is strongly depleted in Pt-group elements. In contrast, the Earth's mantle contained excess oxidants, H2O and Fe2O3, which quantitatively oxidized the admixed Fe from Theia's core, retaining Pt-group elements. In this hypothesis, asteroid impacts were relatively benign with ∼1 terrestrial event that left only thermophile survivors. |
Agosto de 2016
Ocean worlds in the outer solar system
Authors: F. Nimmo, R. T. Pappalardo et al.
Link: Click here
Abstract
Many outer solar system bodies are thought to harbor liquid water oceans beneath their ice shells. This article first reviews how such oceans
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are detected. We then discuss how they are maintained, when they formed, and what the oceans' likely characteristics are. We focus in particular on Europa, Ganymede, Callisto, Titan, and Enceladus, bodies for which there is direct evidence of subsurface oceans. We also consider candidate ocean worlds such as Pluto and Triton. |
Agosto de 2016
Revisiting the Canterbury earthquake sequence after the 14 February 2016 Mw 5.7 event
Authors: Matthew W. Herman and Kevin P. Furlong.
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Abstract
On 14 February 2016, an Mw 5.7 (GNS Science moment magnitude) earthquake ruptured offshore east of Christchurch, New Zealand. This earthquake occurred in an area that had previously experienced significant seismicity from 2010-2012 during the Canterbury earthquake sequence, starting with the 2010 Mw 7.0 Darfield earthquake, and including four Mw ~6.0 |
earthquakes near Christchurch. We determine source parameters for the February 2016 event and its aftershocks, relocate the recent events along with the Canterbury earthquakes, and compute Coulomb stress changes resolved onto the recent events and throughout the greater Christchurch region. Because the February 2016 earthquake occurred close to previous seismicity, the Coulomb stress changes resolved onto its nodal planes are uncertain. However, in the greater Christchurch region, there are areas that remain positively loaded, including beneath the city of Christchurch. The recent earthquake and regional stress changes suggest faults in these regions may pose a continuing seismic hazard. |
Agosto de 2016
Validating induced seismicity forecast models - Induced Seismicity Test Bench
Authors: Eszter Király-Proag, J. Douglas Zechar et al.
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Abstract
Induced earthquakes often accompany fluid injection, and the seismic hazard they pose threatens various underground engineering projects. Models to monitor and control induced seismic hazard with traffic light systems should be probabilistic, forward-looking, and updated as new data arrive. In this study, we propose an Induced Seismicity Test Bench to test and rank such models; this test bench can be used for model development, model selection, and
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ensemble model building. We apply the test bench to data from the Basel 2006 and Soultz-sous-Forêts 2004 geothermal stimulation projects, and we assess forecasts from two . models: Shapiro and Smoothed Seismicity (SaSS) and Hydraulics and Seismics (HySei). These models incorporate a different mix of physics-based elements and stochastic representation of the induced sequences. Our results show that neither model is fully superior to the other. Generally, HySei forecasts the seismicity rate better after shut-in, but is only mediocre at forecasting the spatial distribution. On the other hand, SaSS forecasts the spatial distribution better and gives better seismicity rate estimates before shut-in. The shut-in phase is a difficult moment for both models in both reservoirs: the models tend to underpredict the seismicity rate around, and shortly after, shut-in |
Agosto de 2016
Evidence for universal earthquake rupture initiation behavior
Authors: Men-Andrin Meier, Thomas Heaton et al. Link: Click here
Abstract
Earthquake onsets provide a unique opportunity to study physical rupture processes because they are more easily observable than later rupture stages. Despite this relative simplicity, the observational basis for rupture onsets is unclear. Numerous reports of evidence for magnitude-
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dependent rupture onsets (which imply deterministic rupture behavior) stand in contradiction to a large body of physics-based rupture modeling efforts, which are mostly based on inherently nondeterministic principles. Here we make use of the abundance of short-distance recordings available today; a magnitude dependency of onsets should appear most prominently in such recordings. We use a simple method to demonstrate that all ruptures in the studied magnitude range (4 < M < 8) share a universal initial rupture behavior and discuss ensuing implications for physical rupture processes and earthquake early warning. |
Agosto de 2016
Probability distributions of bed load particle velocities, accelerations, hop distances, and travel times informed by Jaynes's principle of maximum entropy
Authors: David Jon Furbish, Mark W. Schmeeckle et al.
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Abstract
We describe the most likely forms of the probability distributions of bed load particle velocities, accelerations, hop distances, and travel times, in a manner that formally appeals to inferential statistics while honoring mechanical and kinematic constraints imposed by equilibrium transport conditions. The analysis is based on E. Jaynes's elaboration of the implications of the similarity between the Gibbs entropy in statistical
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mechanics and the Shannon entropy in information theory. By maximizing the information entropy of a distribution subject to known constraints on its moments, our choice of the form of the distribution is unbiased. The analysis suggests that particle velocities and travel times are exponentially distributed and that particle accelerations follow a Laplace distribution with zero mean. Particle hop distances, viewed alone, ought to be distributed exponentially. However, the covariance between hop distances and travel times precludes this result. Instead, the covariance structure suggests that hop distances follow a Weibull distribution. These distributions are consistent with high-resolution measurements obtained from high-speed imaging of bed load particle motions. The analysis brings us closer to choosing distributions based on our mechanical insight. |
Agosto de 2016
Modeling tsunami observations to evaluate a proposed late tsunami earthquake stage for the 16 September 2015 Illapel, Chile, Mw 8.3 earthquake
Authors: Thorne Lay, Linyan Li et al.
Link: Click here
Abstract
Resolving seaward extent of slip during great subduction zone interplate ruptures using land-based seismological and geodetic observations is challenging. Modeling of tsunami recordings from ocean-bottom pressure sensors of the Deep-ocean Assessment and Reporting of Tsunami (DART) network has added valuable |
constraints on near-trench slip for recent events. We use DART and tide gauge recordings to evaluate a proposed seismological scenario involving a late Mw 8.08 tsunami earthquake following the ~95 s long main rupture stage of the 16 September 2015 Illapel, Chile, Mw 8.3 earthquake. Tsunami observations constrain the spatial extent of any late tsunami earthquake slip to locate north of the main shock hypocenter. The proposed late shallow slip predicts tsunami signals with considerable amplitudes but shorter wavelengths compared to those of the main stage slip constrained by joint seismic and tsunami modeling, yielding overprediction of first-arrival amplitudes at DART and tide gauge stations when the two stages are combined. |
Agosto de 2016
An integrated analysis of the March 2015 Atacama floods
Authors:Andrew C. Wilcox, Cristian Escauriaza et al. Link: Click here
Abstract
In March 2015 unusual ocean and atmospheric conditions produced many years' worth of rainfall in a ~48 h period over northern Chile's Atacama Desert, one of Earth's driest regions, resulting in catastrophic flooding. Here we describe the hydrologic and geomorphic drivers of and responses to the 2015 Atacama floods. In the
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Salado River, we estimated a flood peak discharge of approximately 1000 m3/s, which caused widespread damage and high sediment loads that were primarily derived from valley-fill erosion; hillslopes remained surprisingly intact despite their lack of vegetation. In the coastal city of Chañaral, flooding of the Salado River produced maximum water depths over 4.5 m, meters thick mud deposition in buildings and along city streets, and coastal erosion. The Atacama flooding has broad implications in the context of hazard reduction, erosion of contaminated legacy mine tailings, and the Atacama's status as a terrestrial analog for Mars. |
Agosto de 2016
Coulomb stress evolution in a diffuse plate boundary: 1400 years of earthquakes in eastern California and western Nevada, USA
Authors:Alessandro Verdecchia and Sara Carena
Link: Click here
Abstract
Diffuse plate boundaries are characterized by deformation distributed over a wide area in a complex network of active faults and by relatively low strain rates. These characteristics make it difficult to understand the spatial and temporal distribution of seismicity. The area east of the Sierra Nevada, between longitudes 121°W and 116°W, is part of a diffuse plate boundary. At least 17 major surface-rupturing earthquakes have happened here in the last 1400 years. Our purpose is to determine whether these events
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influence each other or whether they are randomly distributed in time and space. We model the evolution of coseismic and postseismic Coulomb failure stress changes (ΔCFS) produced by these earthquakes, and we also model interseismic stresses on the entire fault network. Our results show that 80% of the earthquake ruptures are located in areas of combined coseismic and postseismic ΔCFS ≥ 0.2 bar. This relationship is robust, as shown by the control tests that we carried out using random earthquake sequences. We also show that the Fish Lake Valley, Pyramid Lake, and Honey Lake faults have accumulated 45, 37, and 27 bars, respectively, of total ΔCFS (i.e., coseismic + postseismic + interseismic) in the last 1400 years. Such values are comparable to the average stress drop in a major earthquake, and these three faults may be therefore close to failure. |
Julio de 2016
Reconsidering earthquake scaling
Authors: J. Gomberg, A. Wech et al
Link: Click here
Abstract
The relationship (scaling) between scalar moment, M0, and duration, T, potentially provides key constraints on the physics governing fault slip. The prevailing interpretation of M0-T observations proposes different scaling for fast (earthquakes) and slow (mostly aseismic) slip populations and thus fundamentally different driving mechanisms. |
We show that a single model of slip events within bounded slip zones may explain nearly all fast and slow slip M0-T observations, and both slip populations have a change in scaling, where the slip area growth changes from 2-D when too small to sense the boundaries to 1-D when large enough to be bounded. We present new fast and slow slip M0-T observations that sample the change in scaling in each population, which are consistent with our interpretation. We suggest that a continuous but bimodal distribution of slip modes exists and M0-T observations alone may not imply a fundamental difference between fast and slow slip. |
Julio de 2016
Large ionospheric disturbances produced by the HAARP HF facility
Authors: Paul A. Bernhardt, Carl L. Siefring et al
Link: Click here
Abstract
The enormous transmitter power, fully programmable antenna array, and agile frequency generation of the High Frequency Active Auroral Research Program (HAARP) facility in Alaska have allowed the production of unprecedented disturbances in the ionosphere. Using both pencil beams and conical (or twisted) beam transmissions, artificial ionization clouds have been generated near the second, third, fourth, and sixth harmonics of the electron gyrofrequency. The conical beam has been used to sustain these
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clouds for up to 5?h as opposed to less than 30?min durations produced using pencil beams. The largest density plasma clouds have been produced at the highest harmonic transmissions. Satellite radio transmissions at 253?MHz from the National Research Laboratory TACSat4 communications experiment have been severely disturbed by propagating through artificial plasma regions. The scintillation levels for UHF waves passing through artificial ionization clouds from HAARP are typically 16?dB. This is much larger than previously reported scintillations at other HF facilities which have been limited to 3?dB or less. The goals of future HAARP experiments should be to build on these discoveries to sustain plasma densities larger than that of the background ionosphere for use as ionospheric reflectors of radio signals. |
Julio de 2016
Modeling tsunami observations to evaluate a proposed late tsunami earthquake stage for the 16 September 2015 Illapel, Chile, MW 8.3 earthquake
Authors: MThorne Lay, Linyan Li et al
Link: Click here
Abstract
Resolving seaward extent of slip during great subduction zone interplate ruptures using land-based seismological and geodetic observations is challenging. Modeling of tsunami recordings from ocean-bottom pressure sensors of the Deep-ocean Assessment and Reporting of Tsunami (DART) network has added valuable constraints on near-trench slip for recent events. |
We use DART and tide gauge recordings to evaluate a proposed seismological scenario involving a late MW 8.08 tsunami earthquake following the ~95?s long main rupture stage of the 16 September 2015 Illapel, Chile, MW 8.3 earthquake. Tsunami observations constrain the spatial extent of any late tsunami earthquake slip to locate north of the mainshock hypocenter. The proposed late shallow slip predicts tsunami signals with considerable amplitudes but shorter wavelengths compared to those of the main stage slip constrained by joint seismic and tsunami modeling, yielding over-prediction of first-arrival amplitudes at DART and tide gauge stations when the two stages are combined. |
Julio de 2016
Coulomb stress evolution in a diffuse plate boundary: 1400?years of earthquakes in eastern California and western Nevada, USA
Authors: Alessandro Verdecchia and Sara Carena
Link: Click here
Abstract
Diffuse plate boundaries are characterized by deformation distributed over a wide area in a complex network of active faults, and by relatively low strain rates. These characteristics make it difficult to understand the spatial and temporal distribution of seismicity. The area east of the Sierra Nevada, between longitudes 121° W and 116° W, is part of a diffuse plate boundary. At least seventeen major surface-rupturing earthquakes have happened here in the last 1400?years. Our purpose is to determine whether these events influence each other, or whether they are
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randomly distributed in time and space. We model the evolution of coseismic and postseismic Coulomb failure stress changes (?CFS) produced by these earthquakes, and we also model interseismic stresses on the entire fault network. Our results show that 80% of the earthquake ruptures are located in areas of combined coseismic and postseismic ?CFS?=?0.2?bar. This relationship is robust, as shown by the control tests that we carried out using random earthquake sequences. We also show that the Fish Lake Valley, Pyramid Lake, and Honey Lake faults have accumulated 45, 37 and 27 bars respectively of total ?CFS (i.e. coseismic?+?postseismic?+?interseismic) in the last 1400?years. Such values are comparable to the average stress drop in a major earthquake, and these three faults may be therefore close to failure. |
Julio de 2016
Conceptualizing sociohydrological drought processes: The case of the Maya collapse
Authors: Linda Kuil, Gemma Carr et al
Link: Click here
Abstract
With population growth, increasing water demands and climate change the need to understand the current and future pathways to water security is becoming more pressing. To contribute to addressing this challenge, we examine the link between water stress and society through socio-hydrological modeling. We conceptualize the interactions between an agricultural society with its environment in a stylized way. We apply the model to the case of
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the ancient Maya, a population that experienced a peak during the Classic Period (AD 600-830) and then declined during the ninth century. The hypothesis that modest drought periods played a major role in the society's collapse is explored. Simulating plausible feedbacks between water and society we show that a modest reduction in rainfall may lead to an 80% population collapse.Population density and crop sensitivity to droughts, however, may play an equally important role. The simulations indicate that construction of reservoirs results in less frequent drought impacts, but if the reservoirs run dry, drought impact may be more severe and the population drop may be larger. Index terms: 1812 Drought (4303) 1834 Human impacts (4323) 4330 Vulnerability. Keywords: socio-hydrology, Ancient Maya, drought, vulnerability. |
Julio de 2016
How a complex basaltic volcanic system works: constraints from integrating seismic, geodetic and petrological data at Mt. Etna volcano during the July-August 2014 eruption
Authors: Marco Viccaro, Francesco Zuccarello et al
Link: Click here
Abstract
Integrating geodetic, seismic and petrological data for a recent eruptive episode at Mt. Etna has enabled us to define the history of magma storage and transfer within the multi-level structure of the volcano, providing spatial and temporal constraints for magma movements before the eruption. Geodetic data related to the July-August 2014 activity provide evidence of a magma reservoir at ~4?km bsl. This reservoir pressurized from late March 2014 and fed magmas that were then erupted from vents on the lower eastern flank of North-East Crater (NEC) and at New South-East Crater (NSEC) summit
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crater during the July eruptive activity. Magma drainage caused its depressurization since mid-July. Textural and micro-analytical data obtained from plagioclase crystals indicate similar disequilibrium textures and compositions at the cores in lavas erupted at the base of NEC and NSEC, suggesting comparable deep histories of evolution and ascent. Conversely, the compositional differences observed at the crystal rims have been associated to distinct degassing styles during storage in a shallow magma reservoir. Seismic data have constrained depth for a shallow part of the plumbing system at 1-2?km asl. Timescales of magma storage and transfer have also been calculated through diffusion modeling of zoning in olivine crystals of the two systems. Our data reveal a common deep history of magmas from the two systems, which is consistent with a recharging phase by more mafic magma between late March and early June 2014. Later, the magma continued its crystallization under distinct chemical and physical conditions at shallower levels. |
Julio de 2016
Were the May 2012 Emilia-Romagna earthquakes induced? A coupled flow-geomechanics modeling assessment
Authors: R. Juanes, B. Jha et al
Link: Click here
Abstract
Seismicity induced by fluid injection and withdrawal has emerged as a central element of the scientific discussion around subsurface technologies that tap into water and energy resources. Here we present the application of coupled flow-geomechanics simulation technology to the post mortem analysis of a
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sequence of damaging earthquakes (Mw?=?6.0 and 5.8) in May 2012 near the Cavone oil field, in northern Italy. This sequence raised the question of whether these earthquakes might have been triggered by activities due to oil and gas production. Our analysis strongly suggests that the combined effects of fluid production and injection from the Cavone field were not a driver for the observed seismicity. More generally, our study illustrates that computational modeling of coupled flow and geomechanics permits the integration of geologic, seismotectonic, well log, fluid pressure and flow rate, and geodetic data and provides a promising approach for assessing and managing hazards associated with induced seismicity. |
Julio de 2016
Can slip heterogeneity be linked to earthquake recurrence?
Authors: Kate Huihsuan Chen, Iyin Chen et al
Link: Click here
Abstract
The rupture process of two M4 repeating earthquake sequences in eastern Taiwan with contrasting recurrence behavior is investigated to demonstrate a link between slip heterogeneity and earthquake recurrence. The M3.6–3.8 quasiperiodic repeating earthquakes characterized by 3?years recurrence interval reveal overlapped slip concentrations. Inferred
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slip distribution for each event illustrates two asperities with peak slip of 47.7?cm and peak stress drop of 151.1?MPa. Under the influence of nearby M6.9 event, the M4.3–4.8 repeating earthquakes separated only by 6–87?min, however, reveal an aperiodic manner. There is a distinct rupture characteristic without overlap in the slip areas, suggesting that shortening of the recurrence interval by the nearby large earthquake may change the slip heterogeneity in a repeatedly ruptured asperity. We conclude that the inherent heterogeneity of stress and strength could influence the distribution of coseismic slip, which is strongly tied to the recurrence behavior. |
Julio de 2016
A distinct source and differentiation history for Kolumbo submarine volcano, Santorini volcanic field, Aegean arc
Authors: Martijn Klaver, Steven Carey et al
Link: Click here
Abstract
This study reports the first detailed geochemical characterization of Kolumbo submarine volcano in order to investigate the role of source heterogeneity in controlling geochemical variability within the Santorini volcanic field in the central Aegean arc. Kolumbo, situated 15 km to the northeast of Santorini, last erupted in 1650 AD and is thus closely associated with the Santorini volcanic system in space and time. Samples taken by remotely-operated vehicle that were analyzed for major element, trace element and Sr-Nd-Hf-Pb isotope composition include the 1650 AD and underlying K2 rhyolitic, enclave-bearing pumices that are nearly identical in composition
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(73 wt. % SiO2, 4.2 wt. % K2O). Lava bodies exposed in the crater and enclaves are basalts to andesites (52-60 wt. % SiO2). Biotite and amphibole are common phenocryst phases, in contrast with the typically anhydrous mineral assemblages of Santorini. The strong geochemical signature of amphibole fractionation and the assimilation of lower crustal basement in the petrogenesis of the Kolumbo magmas indicates that Kolumbo and Santorini underwent different crustal differentiation histories and that their crustal magmatic systems are unrelated. Moreover, the Kolumbo samples are derived from a distinct, more enriched mantle source that is characterized by high Nb/Yb (>3) and low 206Pb/204Pb (<18.82) that has not been recognized in the Santorini volcanic products. The strong dissimilarity in both petrogenesis and inferred mantle sources between Kolumbo and Santorini suggests that pronounced source variations can be manifested in arc magmas that are closely associated in space and time within a single volcanic field. |
Julio de 2016
Hazards without disasters
Author: Marcia McNutt
Link: Click here
Abstract
A natural hazard need not become a human disaster if society learns and applies lessons in preparation and resilience. Earthquake history speaks well to this—engineered structures need to stand up to strong shaking. Chile learned this lesson before its 2010 earthquake of magnitude 8.8. Because it had already enforced seismic provisions of building codes, there was little loss of life due to damage to buildings. Engineered structures also performed very well during the giant 2011 Tohoku earthquake in northeast Japan; however, approximately 20,000 lives were lost to the ensuing tsunami. What survival strategies are available for communities at risk for tsunamis?
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Julio de 2016
Gradual caldera collapse at Bárdarbunga volcano, Iceland, regulated by lateral magma outflow
Authors: JMagnús T. Gudmundsson, Kristín Jónsdóttir et al
Link: Click here
Abstract
The Bárdarbunga caldera volcano in central Iceland collapsed from August 2014 to
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February 2015 during the largest eruption in Europe since 1784. An ice-filled subsidence bowl, 110 square kilometers (km2) in area and up to 65 meters (m) deep developed, while magma drained laterally for 48 km along a subterranean path and erupted as a major lava flow northeast of the volcano. Our data provide unprecedented insight into the workings of a collapsing caldera. |
Julio de 2016
Asteroid bombardment and the core of Theia as possible sources for the Earth's late veneer component
Author: Norman H. Sleep
Link: Click here
Abstract
The silicate Earth contains Pt-group elements in roughly chondritic relative ratios, but with absolute concentrations <1% chondrite. This veneer implies addition of chondrite-like material with 0.3–0.7% mass of the Earth's mantle or an equivalent planet-wide thickness of 5–20 km. The veneer thickness, 200–300 m, within the lunar crust and mantle is much less. One hypothesis is that the terrestrial veneer arrived after the moon-forming impact within a few large asteroids that happened to miss the smaller Moon. Alternatively, most of terrestrial veneer came from the core of the moon-forming impactor, Theia. The Moon then |
likely contains iron from Theia's core. Mass balances lend plausibility. The lunar core mass is ∼1.6 × 1021 kg and the excess FeO component in the lunar mantle is 1.3–3.5 × 1021 kg as Fe, totaling 3–5 × 1021 kg or a few percent of Theia's core. This mass is comparable to the excess Fe of 2.3–10 × 1021 kg in the Earth's mantle inferred from the veneer component. Chemically in this hypothesis, Fe metal from Theia's core entered the Moon-forming disk. H2O and Fe2O3 in the disk oxidized part of the Fe, leaving the lunar mantle near a Fe-FeO buffer. The remaining iron metal condensed, gathered Pt-group elements eventually into the lunar core. The silicate Moon is strongly depleted in Pt-group elements. In contrast, the Earth's mantle contained excess oxidants, H2O and Fe2O3, which quantitatively oxidized the admixed Fe from Theia's core, retaining Pt-group elements. In this hypothesis, asteroid impacts were relatively benign with ∼1 terrestrial event that left only thermophile survivors. |
Julio de 2016
Explicación de elevación geodésica por medio de inyección de magma en un depósito de larga vida: aplicación a la actividad 2007-2014 observados en el campo volcánico Laguna de Maule, Chile
Autores:Hélène Le Mével, Patricia Gregg et al
Link: Clic aquí
Abstract
Yendo más allá de los modelos cinemáticos ampliamente utilizados para estudiar las fuentes en deformación, aquí presentamos un nuevo modelo dinámico para describir el proceso de inyección de magma en un depósito de magma existente. Para validar este modelo, nosotros llegamos a una solución analítica y comparamos sus resultados con los que se obtienen utilizando el método de elementos finitos. [El magma], un fluido newtoniano que se caracteriza por su viscosidad, densidad y sobrepresión (respecto del valor litostático) fluye a través de un conducto vertical, llegando a un depósito incrustado en un dominio elástico [la cámara magmática], lo que lleva a un aumento en la presión del yacimiento y a una deformación de la superficie en función del tiempo. Aplicamos nuestro modelo de inyección a los datos Interferométricos del Radar de Apertura Sintética (InSAR) a la secuencia de eventos iniciados en el año 2007 y que están ocurriendo en el campo volcánico de Laguna del Maule. Utilizando una red de búsqueda de optimización, minimizamos el desajuste de los datos de desplazamiento InSAR y variamos los tres parámetros que rigen la solución analítica, es decir: la escala de tiempo característico para la propagación del magma, la presión máxima de inyección, y el tiempo de inflexión cuando los interruptores de aceleración pasa de de positivo a negativo. Para un esferoide con semieje mayor a = 6200 m y semi-eje menor c = 100 m, que se encuentra a una profundidad de 4,5 km en un semiespacio elástico puro, el mejor ajuste a los datos de desplazamiento InSAR se produce para τP = 9.5 años con un incremento de presión hasta los 11,5 MPa durante dos años de inyección de presión. El flujo volumétrico se incrementó a 1.2 m3 / s durante dos años y luego se redujo a 0.7 m3 / s en el año 2014. Esto significa que en 7.3 años, se inyectaron al menos 187 millones de metros cúbicos de magma.
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Julio de 2016
Magma injection into a long-lived reservoir to explain geodetically measured uplift: application to the 2007–2014 unrest episode at Laguna del Maule volcanic field, Chile
Authors:Hélène Le Mével, Patricia Gregg et al
Link: Click here
Abstract
Moving beyond the widely used kinematic models for the deformation sources, we present a new dynamic model to describe the process of injecting magma into an existing magma reservoir. To validate this model, we derive an analytical solution and compare its results to those calculated using the Finite Element Method. A Newtonian fluid characterized by its viscosity, density, and overpressure (relative to the lithostatic value) flows through a vertical conduit, intruding into a reservoir embedded in an elastic domain, leading to an increase in reservoir pressure and time-dependent surface deformation. We apply our injection model to Interferometric Synthetic Aperture Radar (InSAR) data from the ongoing unrest episode at Laguna del Maule (Chile) volcanic field that started in 2007. Using a grid search optimization, we minimize the misfit to the InSAR displacement data and vary the three parameters governing the analytical solution: the characteristic timescale τP for magma propagation, the maximum injection pressure, and the inflection time when the acceleration switches from positive to negative. For a spheroid with semi-major axis a = 6200 m, semi-minor axis c= 100 m, located at a depth of 4.5 km in a purely elastic half-space, the best fit to the InSAR displacement data occurs for τP= 9.5 years and an injection pressure rising up to 11.5 MPa for two years. The volume flow rate increased to 1.2 m3/s for two years and then decreased to 0.7 m3/s in 2014. In 7.3 years, at least 187 million cubic meters of magma was injected. |
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Laguna del Maule - Posible explosión cataclísmica (VEI=4, mínimo), 187 millones de m3 dinámicos, 1.2 m3/s de lava |
Julio de 2016
A Bayesian source model for the 2004 great Sumatra-Andaman earthquake
Authors: Quentin Bletery, Anthony Sladen et al
Link: Click here
Abstract
The 2004 Mw 9.1–9.3 Sumatra-Andaman earthquake is one of the largest earthquakes of the modern instrumental era. Despite considerable efforts to analyze this event, the different available observations have proven difficult to reconcile in a single finite-fault slip model. In particular, the critical near-field geodetic records contain variable and significant postseismic signal (between 2 weeks' and 2 months' worth), while the satellite altimetry records of the associated tsunami are affected by various sources of uncertainties (e.g., source rupture velocity and mesoscale oceanic currents). In this study, we investigate the quasi-static slip distribution of the Sumatra-Andaman earthquake by carefully accounting for the different sources of uncertainties in the joint inversion of available
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geodetic and tsunami data. To this end, we use nondiagonal covariance matrices reflecting both observational and modeling uncertainties in a fully Bayesian inversion framework. Modeling errors can be particularly large for great earthquakes. Here we consider a layered spherical Earth for the static displacement field, nonhydrostatic equations for the tsunami, and a 3-D megathrust interface geometry to alleviate some of the potential epistemic uncertainties. The Bayesian framework then enables us to derive families of possible models compatible with the unevenly distributed and sometimes ambiguous measurements. We infer two regions of high fault slip at 3°N–4°N and 7°N–8°N with amplitudes that likely reach values as large as 40 m and possibly larger. These values are a factor of 2 larger than typically found in previous studies—potentially an outcome of commonly assumed forms of regularization. Finally, we find that fault rupture very likely involved shallow slip. Within the resolution provided by the existing data, we cannot rule out the possibility that fault rupture reached the trench. |
Julio de 2016
Aftershocks
Author: Sebastiano D'Amico
Link: Click here
Abstract
Traditionally, when scientists discuss earthquakes, we talk about geology and seismology, infrastructure and engineering, as well as management strategies for minimizing human and material losses. Nevertheless, the study of an earthquake's effect on the social
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and cultural elements of a community can help us understand how different societies have evolved and adapted over time and how cities have built up their relative capacity to withstand future large seismic events. In fact, as Andrew Robinson describes in his new book, Earth-Shattering Events, the effects of an earthquake can reverberate throughout a society's identity. In some cases, they have played a catalyzing role in the evolution of urban and architectural style and have irrevocably altered the communities in question. |
Julio de 2016
A Bayesian source model for the 2004 great Sumatra-Andaman earthquake
Authors: Quentin Bletery, Anthony Sladen et al
Link: Click here
Abstract
The 2004 Mw 9.1-9.3 Sumatra-Andaman earthquake is one of the largest earthquakes of the modern instrumental era. Despite considerable efforts to analyze this event, the different available observations have proven difficult to reconcile in a single finite-fault slip model. In particular, the critical near-field geodetic records contain variable and significant post-seismic signal (between 2 weeks' and 2 months' worth) while the satellite altimetry records of the associated tsunami are affected by various sources of uncertainties (e.g., source rupture velocity and meso-scale oceanic currents). In this study, we investigate the quasi-static slip distribution of the Sumatra-Andaman earthquake by carefully accounting for the different sources of uncertainties in the joint inversion of available
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geodetic and tsunami data. To this end, we use non-diagonal covariance matrices reflecting both observational and modeling uncertainties in a fully Bayesian inversion framework. Modeling errors can be particularly large for great earthquakes. Here, we consider a layered spherical Earth for the static displacement field, non-hydrostatic equations for the tsunami and a 3D megathrust interface geometry to alleviate some of the potential epistemic uncertainties. The Bayesian framework then enables us to derive families of possible models compatible with the unevenly distributed and sometimes ambiguous measurements. We infer two regions of high fault slip at 3∘N-4∘N and 7∘N-8∘N with amplitudes that likely reach values as large as 40 m and possibly larger. These values are a factor of two larger than typically found in previous studies - potentially an outcome of commonly assumed forms of regularization. Finally, we find that fault rupture very likely involved shallow slip. Within the resolution provided by the existing data, we cannot rule out the possibility that fault rupture reached the trench. |
Julio de 2016
The permanently shadowed regions of dwarf planet Ceres
Authors: Norbert Schorghofer, Erwan Mazarico et al
Link: Click here
Abstract
Ceres has only a small spin axis tilt (4°), and craters near its rotational poles can experience permanent shadow and trap volatiles, as is the case on Mercury and on Earth's Moon. Topography derived from stereo imaging by the Dawn spacecraft is used to calculate direct
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solar irradiance that defines the extent of the permanently shadowed regions (PSRs). Inthe northern polar region, PSRs cover ∼1800 km2 or 0.13% of the hemisphere, and most of the PSRs are cold enough to trap water ice over geological time periods. Based on modeling of the water exosphere, water molecules seasonally reside around the winter pole and ultimately an estimated 0.14% of molecules get trapped. Even for the lowest estimates of the amount of available water, this predicts accumulation rates in excess of loss rates, and hence, there should be fresh ice deposits in the cold traps. |
Julio de 2016
Were the May 2012 Emilia-Romagna earthquakes induced? A coupled flow-geomechanics modeling assessment
Authors: R. Juanes, B. Jha et al
Link: Click here
Abstract
Seismicity induced by fluid injection and withdrawal has emerged as a central element of the scientific discussion around subsurface technologies that tap into water and energy resources. Here we present the application of coupled flow-geomechanics simulation technology to the post mortem analysis of a
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sequence of damaging earthquakes (Mw = 6.0 and 5.8) in May 2012 near the Cavone oil field, in northern Italy. This sequence raised the question of whether these earthquakes might have been triggered by activities due to oil and gas production. Our analysis strongly suggests that the combined effects of fluid production and injection from the Cavone field were not a driver for the observed seismicity. More generally, our study illustrates that computational modeling of coupled flow and geomechanics permits the integration of geologic, seismotectonic, well log, fluid pressure and flow rate, and geodetic data and provides a promising approach for assessing and managing hazards associated with induced seismicity. |
Julio de 2016
Three-dimensional distribution of ionospheric anomalies prior to three large earthquakes in Chile
Authors: Liming He and Kosuke Heki
Link: Click here
Abstract
Using regional Global Positioning System (GPS) networks, we studied three-dimensional spatial structure of ionospheric total electron content (TEC) anomalies preceding three recent large earthquakes in Chile, South America, i.e. the 2010 Maule (Mw8.8), the 2014 Iquique (Mw8.2), and the
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2015 Illapel (Mw8.3) earthquakes. Both positive and negative TEC anomalies, with areal extent dependent on the earthquake magnitudes, appeared simultaneously 20-40 minutes before the earthquakes. For the two mid-latitude earthquakes (2010 Maule and 2015 Illapel), positive anomalies occurred to the north of the epicenters at altitudes 150-250 km. The negative anomalies occurred further to the north at higher altitudes 200-500 km. This lets the epicenter, the positive and negative anomalies align parallel with the local geomagnetic field, which is a typical structure of ionospheric anomalies occurring in response to positive surface electric charges. |
Julio de 2016
Thermal equation of state of hcp-iron: Constraint on the density deficit of Earth's solid inner core
Authors:Yingwei Fei, Caitlin Murphy et al
Link: Click here
Abstract
We conducted high-pressure experiments on hexagonal close packed iron (hcp-Fe) in MgO, NaCl, and Ne pressure-transmitting media and found general agreement among the experimental data at 300 K that yield the best fitted values of the bulk modulus K0 = 172.7(±1.4) GPa and its pressure derivative
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K0′ = 4.79(±0.05) for hcp-Fe, using the third-order Birch-Murnaghan equation of state. Using the derived thermal pressures for hcp-Fe up to 100 GPa and 1800 K and previous shockwave Hugoniot data, we developed a thermal equation of state of hcp-Fe. The thermal equation of state of hcp-Fe is further used to calculate the densities of iron along adiabatic geotherms to define the density deficit of the inner core, which serves as the basis for developing quantitative composition models of the Earth's inner core. We determine the density deficit at the inner core boundary to be 3.6%, assuming an inner core boundary temperature of 6000 K. |
Julio de 2016
Real-time forecast of aftershocks from a single seismic station signal
Authors:E. Lippiello, A. Cirillo et al
Link: Click here
Abstract
The evaluation of seismic hazard in the hours following large earthquakes is strongly affected by biases due to difficulties in determining earthquake location. This leads to the huge incompleteness of instrumental catalogs. Here we show that if, on the one hand, the overlap of aftershock coda waves hides many small events,
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on the other hand, it leads to a well-determined empirical law controlling the decay of the amplitude of the seismic signal at a given site. The fitting parameters of this law can be related to those controlling the temporal decay of the aftershock number, and it is then possible to obtain short-term postseismic occurrence probability from a single recorded seismic signal. We therefore present a novel procedure which, without requiring earthquake location, produces more accurate and almost real-time forecast, in a site of interest, directly from the signal of a seismic station installed at that site |
Julio de 2016
Induced earthquake magnitudes are as large as (statistically) expected
Authors: Nicholas J. van der Elst, Morgan T. Page et al
Link: Click here
Abstract
A major question for the hazard posed by injection-induced seismicity is how large induced earthquakes can be. Are their maximum magnitudes determined by injection parameters or by tectonics? Deterministic limits on induced earthquake magnitudes have been proposed based on the size of the reservoir or the volume of fluid injected. However, if induced earthquakes occur on tectonic faults oriented favorably with respect to the tectonic stress field, then they may be limited only by the regional tectonics and connectivity of the fault network. In this study, we show that the largest magnitudes observed at fluid injection sites are consistent with the |
show that the largest magnitudes observed at fluid injection sites are consistent with the sampling statistics of the Gutenberg-Richter distribution for tectonic earthquakes, assuming no upper magnitude bound. The data pass three specific tests: (1) the largest observed earthquake at each site scales with the log of the total number of induced earthquakes, (2) the order of occurrence of the largest event is random within the induced sequence, and (3) the injected volume controls the total number of earthquakes rather than the total seismic moment. All three tests point to an injection control on earthquake nucleation but a tectonic control on earthquake magnitude. Given that the largest observed earthquakes are exactly as large as expected from the sampling statistics, we should not conclude that these are the largest earthquakes possible. Instead, the results imply that induced earthquake magnitudes should be treated with the same maximum magnitude bound that is currently used to treat seismic hazard from tectonic earthquakes |
Julio de 2016
Can slip heterogeneity be linked to earthquake recurrence?
Authors: Kate Huihsuan Chen, Iyin Chen et al
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Abstract
The rupture process of two M4 repeating earthquake sequences in eastern Taiwan with contrasting recurrence behavior is investigated to demonstrate a link between slip heterogeneity and earthquake recurrence. The M3.6–3.8 quasi-periodic repeating earthquakes characterized by 3-yr recurrence interval reveal overlapped slip concentrations. Inferred slip distribution for each
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event illustrates two asperities with peak slip of 47.69 cm and peak stress drop of 155.11 MPa. Under the influence of nearby M6.9 event, the M4.3-4.8 repeating earthquakes separated only by 6 - 87 mins however, reveal an aperiodic manner. There is a distinct rupture characteristic without overlap in the slip areas, suggesting that shortening of the recurrence interval by the nearby large earthquake may change the slip heterogeneity in a repeatedly ruptured asperity. We conclude that the inherent heterogeneity of stress and strength may influence the distribution of co-seismic slip, which is strongly tied to the recurrence behavior. |
Junio de 2016
Asteroid bombardment and the core of Theia as possible sources for the Earth's late veneer component
Authors:Norman H. Sleep
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Abstract
The silicate Earth contains Pt-group elements in roughly chondritic relative ratios, but with absolute concentrations <1% chondrite. This veneer implies addition of chondrite-like material with 0.3-0.7% mass of the Earth's mantle or an equivalent planet-wide thickness of 5-20 km. The veneer thickness, 200-300 m, within the lunar crust and mantle is much less. One hypothesis is that the terrestrial veneer arrived after the moon-forming impact within a few large asteroids that happened to miss the smaller Moon. Alternatively, most of terrestrial veneer came from the core of the moon-forming impactor, Theia. The Moon then |
likely contains iron from Theia's core. Mass balances lend plausibility. The lunar core mass is 1.6 × 1021 kg and the excess FeO component in the lunar mantle is 1.3-3.5 × 1021 kg as Fe, totaling 3-5 × 1021 kg or a few percent of Theia's core. This mass is comparable to the excess Fe of 2.3-10 × 1021 kg in the Earth's mantle inferred from the veneer component. Chemically in this hypothesis, Fe metal from Theia's core entered the Moon-forming disk. H2O and Fe2O3 in the disk oxidized part of the Fe, leaving the lunar mantle near a Fe-FeO buffer. The remaining iron metal condensed, gathered Pt-group elements eventually into the lunar core. The silicate Moon is strongly depleted in Pt-group elements. In contrast, the Earth's mantle contained excess oxidants, H2O and Fe2O3, which quantitatively oxidized the admixed Fe from Theia's core, retaining Pt-group elements. In this hypothesis, asteroid impacts was relatively benign with ∼1 terrestrial event that left only thermophile survivors. |
Junio de 2016
Can we manage groundwater? A method to determine the quantitative testability of groundwater management plans
Authors: E. K. White, T. J. Peterson et al
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Abstract
Groundwater is the world's largest freshwater resource and due to overextraction, levels have declined in many regions causing extensive social and environmental impacts. Groundwater management seeks to balance and mitigate the detrimental impacts of development, with plans commonly used to outline management pathways. Thus, plan efficiency is crucial, but seldom are plans systematically and quantitatively assessed for effectiveness. This study frames groundwater management as a system control problem in order to develop a novel testability assessment rubric to determine if plans meet the requirements of a control loop,
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and subsequently, whether they can be quantitatively tested. Seven components of a management plan equivalent to basic components of a control loop were determined, and requirements of each component necessary to enable testability were defined. Each component was weighted based upon proposed relative importance, then segmented into rated categories depending on the degree the requirements were met. Component importance varied but, a defined objective or acceptable impact was necessary for plans to be testable. The rubric was developed within the context of the Australian groundwater management industry, and while use of the rubric is not limited to Australia, it was applied to 15 Australian groundwater management plans and approximately 47% were found to be testable. Considering the importance of effective groundwater management, and the central role of plans, our lack of ability to test many plans is concerning. |
Junio de 2016
Evidence of underground electric current generation during the 2009 L'Aquila earthquake: Real or instrumental?
Authors: F. Masci and J. N. Thomas et al
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We investigate magnetic effects in correspondence of the Mw6.1 L'Aquila earthquake. Magnetic and seismic records are analyzed. Rapid and distinct changes and an offset can be seen in magnetic field components after the main shock. We show that these effects result from electromagnetic induction due to the movement of the sensors through the Earth's
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magnetic field and from a permanent displacement of the sensors from their original position caused by the passing seismic waves. A transient signal in total field data from an overhauser magnetometer apparently occurs in correspondence with the earthquake. Our analysis shows that the transient was not observed by other sensors that were operating in close proximity to the overhauser. Thus, the transient signal in the total magnetic field data, and the offset in the magnetic field components, cannot be associated with a hypothetical underground electric current generated by the earthquake, as suggested by Nenovski (2015). |
Junio de 2016
Mantle control of the geodynamo: Consequences of top-down regulation
Author: Peter Olson
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Abstract
The mantle global circulation, including deep subduction and lower mantle superplumes, exerts first-order controls on the evolution of the core, the history of the geodynamo, and the structure of the geomagnetic field. Mantle global circulation models that include realistic plate motions, deep subduction, and compositional heterogeneity similar to the observed large low seismic velocity provinces in the lower mantle predict that the present-day global average heat flux at the core-mantle boundary (CMB) exceeds 85 mW m−2. This is sufficient to drive the present-
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day geodynamo by thermochemical convection and implies a very young inner core, with inner core nucleation between 400 and 1100 Ma. The mantle global circulation also generates spatially heterogeneous heat flux at the CMB, with peak-to-peak lateral variations exceeding 100 mW m−2. Such extreme lateral variability in CMB heat flux, in conjunction with the high thermal conductivity of the core, implies that the liquid outer core is thermally unstable beneath the high seismic velocity regions in the lower mantle but thermally stable beneath the large low seismic velocity provinces. Numerical dynamo simulations show how this pattern of heterogeneous boundary heat flux affects flow in the outer core, producing localized circulation patterns beneath the CMB tied to the mantle heterogeneity and long-lived deviations from axial symmetry in the geomagnetic field. |
Junio de 2016
Whole planet coupling between climate, mantle, and core: Implications for rocky planet evolution
Authors:
Bradford J. Foley and Peter E. Driscoll
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Abstract
Earth's climate, mantle, and core interact over geologic time scales. Climate influences whether plate tectonics can take place on a planet, with cool climates being favorable for plate tectonics because they enhance stresses in the lithosphere, suppress plate boundary annealing, and promote hydration and weakening of the lithosphere. Plate tectonics plays a vital role in the long-term carbon cycle, which helps to maintain a temperate climate. Plate tectonics provides long-term cooling of the core, which is vital for generating a magnetic field, and the magnetic field is capable of shielding atmospheric volatiles
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from the solar wind. Coupling between climate, mantle, and core can potentially explain the divergent evolution of Earth and Venus. As Venus lies too close to the sun for liquid water to exist, there is no long-term carbon cycle and thus an extremely hot climate. Therefore, plate tectonics cannot operate and a long-lived core dynamo cannot be sustained due to insufficient core cooling. On planets within the habitable zone where liquid water is possible, a wide range of evolutionary scenarios can take place depending on initial atmospheric composition, bulk volatile content, or the timing of when plate tectonics initiates, among other factors. Many of these evolutionary trajectories would render the planet uninhabitable. However, there is still significant uncertainty over the nature of the coupling between climate, mantle, and core. Future work is needed to constrain potential evolutionary scenarios and the likelihood of an Earth-like evolution. |
Junio de 2016
New analytic solutions for modeling vertical gravity gradient anomalies
Authors: Seung-Sep Kim and Paul Wessel
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Abstract
Modern processing of satellite altimetry for use in marine gravimetry involves computing the along-track slopes of observed sea-surface heights, projecting them into east-west and north-south deflection of the vertical grids, and using Laplace's equation to algebraically obtain a grid of the vertical gravity gradient (VGG). The VGG grid is then integrated via overlapping, flat Earth Fourier transforms to yield a free-air anomaly grid. Because of this integration and associated edge
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effects, the VGG grid retains more short-wavelength information (e.g., fracture zone and seamount signatures) that is of particular importance for plate tectonic investigations. While modeling of gravity anomalies over arbitrary bodies has long been a standard undertaking, similar modeling of VGG anomalies over oceanic features is not commonplace yet. Here we derive analytic solutions for VGG anomalies over simple bodies and arbitrary 2-D and 3-D sources. We demonstrate their usability in determining mass excess and deficiency across the Mendocino fracture zone (a 2-D feature) and find the best bulk density estimate for Jasper seamount (a 3-D feature). The methodologies used herein are implemented in the Generic Mapping Tools, available from gmt.soest.hawaii.edu. |
Junio de 2016
Induced earthquake magnitudes are as large as (statistically) expected
Authors: Nicholas J. van der Elst, Morgan T. Page et al
Link: Click here
Abstract
A major question for the hazard posed by injection-induced seismicity is how large induced earthquakes can be. Are their maximum magnitudes determined by injection parameters, or by tectonics? Deterministic limits on induced earthquake magnitudes have been proposed based on the size of the reservoir or the volume of fluid injected. However, if induced earthquakes occur on tectonic faults oriented favorably with respect to the tectonic stress field, then they may be limited only by the regional tectonics and connectivity of the fault network. In this study, we show that the largest magnitudes observed at
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fluid injection sites are consistent with the sampling statistics of the Gutenberg-Richter distribution for tectonic earthquakes, assuming no upper magnitude bound. The data pass three specific tests: 1) the largest observed earthquake at each site scales with the log of the total number of induced earthquakes, 2) the order of occurrence of the largest event is random within the induced sequence, and 3) the injected volume controls the total number of earthquakes, rather than the total seismic moment. All three tests point to an injection control on earthquake nucleation, but a tectonic control on earthquake magnitude. Given that the largest observed earthquakes are exactly as large as expected from the sampling statistics, we should not conclude that these are the largest earthquakes possible. Instead, the results imply that induced earthquake magnitudes should be treated with the same maximum magnitude bound that is currently used to treat seismic hazard from tectonic earthquakes. |
Junio de 2016
The effects of dynamics on the triboelectrification of volcanic ash
Authors: Joshua Méndez Harper and Josef Dufek
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Abstract
Lightning is often observed during explosive volcanic eruptions and the charging processes associated with these displays have been attributed to several mechanisms. In this work we delineate a set of experiments designed to quantify silicate-based triboelectric charging in the volcanic context. Using natural samples from three different volcanoes, we show that the rate of triboelectrification in a fluidized bed depends on |
the energy input into the granular system. Experiments are conducted employing non-intrusive electrostatic sensors, ensuring that all charge exchange arises solely from particle-particle collisions. At higher fluidization energies, particles undergo more frequent and energetic collisions, facilitating the transfer of charge. This finding implies that triboelectric charging could help promote charging in regions of the eruptive system that contain numerous particle-particle collisions such as the conduit and gas-thrust regions. Our experiments also suggest that surface charge density is capped, at least in part, by atmospheric conditions, specifically the breakdown characteristics of the gas. |
