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Noviembre de 2020 Here we test the precursory enhancement in ionospheric total electron content (TEC) which has been reported by Heki (2011, https://doi.org/10.1029/2011GL047908) and numerous Global Navigation Satellite System (GNSS) TEC observational studies before the 2011 Mw9.0 Tohoku Oki and many great earthquakes. We verify the frequency of this TEC enhancement via analysis of a 2‐month vertical TEC (VTEC) time series that includes the Tohoku Oki earthquake using the procedure, based on Akaike's information criterion, and threshold of Heki and Enomoto (2015, https://doi.org/10.1002/2015JA021353). The averaged occurrence rate of the TEC enhancement is much larger than that reported by Heki and Enomoto (2015, https://doi.org/10.1002/2015JA021353) when all of the visible GPS satellites at a given station are taken |
into account. The frequency assessment by Heki and Enomoto (2015, https://doi.org/10.1002/2015JA021353) using only one satellite underestimates the frequency of the TEC enhancement. In fact, the TEC enhancement is sufficiently frequent to explain all the reported enhancements prior to the great earthquakes as a product of chance. We also analyze the spatial distribution of the preseismic TEC enhancement and coseismic TEC depletion for the Tohoku Oki earthquake with the data after reducing intertrace biases. We observe significant postseismic depletion that lasted at least 2 h after the earthquake and extended at least 500 km around the center of the large slip area. This means that evaluation of the enhancements using reference curves which was adopted by Heki (2011, https://doi.org/10.1029/2011GL047908) and even by the recent papers (e.g., He & Heki 2016, https://doi.org/10.1002/2016GL069863; 2017, https://doi.org/10.1002/2017JA024012; 2018, https://doi.org/10.1029/2017JA024871) is in danger of mistaking a large and long lasting postseismic TEC depletion for a preseismic enhancement. |
Noviembre de 2020 Growing infrastructure and increasing population have caused significant loss of life due to recent large earthquakes, with the 2008 Mw 7.9 Wenchuan and 2005 Mw 7.6 Kashmir earthquakes each causing greater than 50,000 deaths. These earthquakes highlight the need for the development of building codes designed to withstand the strong ground shaking caused by earthquakes, as reinforced infrastructure is one of the most important factors for preventing fatalities due to ground |
shaking from earthquakes. Identifying the seismic hazard of a region, or the likelihood of ground shaking at a site due to potential earthquakes over time, is a key ingredient for informing a defensible building code. Here, we focus on current and future advances in how data from the fields of geology and geomorphology contribute to the most widely used type of seismic hazard model. These geologic data represent vital components to seismic hazard models, as they can provide information about the location and types of earthquakes that can occur over long, thousands of years, time periods, that cannot be obtained using other methods. We discuss some of the most pressing scientific issues about these data that are important for the development of seismic hazard models and defensible building codes. |
Noviembre de 2020 For more than three decades, the depleted Rongchang gas reservoir in China’s Sichuan Basin was used for the disposal of unwanted water, which resulted in induced earthquakes, with magnitudes as high as 5.2. After all wells were closed, the frequency of seismic activity was observed to decay |
following a modified Omori law, and since April 2015, seismic activity again began to increase, and a M 4.9 earthquake occurred on Dec. 27. The results of an ETAS model analysis show that forced seismicity accounted for more than 70% of the total events. For most M ≥ 3.5 earthquakes, including two M ≥ 4 events, the estimated overpressure was lower than the maximum injection pressure. These results, coupled with the fact that post injection seismic activity has similar characteristics to seismicity during injection, indicate that the injected overpressure fluid was still the driving factor for post injection seismic activity. |
Octubre de 2020 Hydraulic fracturing (HF) is a technique that is used for extracting petroleum resources from impermeable host rocks. In this process, fluid injected under high pressure causes fractures to propagate. This technique has been transformative for the hydrocarbon industry, unlocking otherwise stranded resources; however, environmental concerns make HF controversial. One concern is HF‐induced seismicity, since fluids driven under high pressure also have the potential to reactivate faults. Controversy has inevitably followed these HF-induced earthquakes, with economic and human losses from ground shaking at one extreme and moratoriums on resource development at the other. Here, we review the state of knowledge of this |
category of induced seismicity. We first cover essential background information on HF along with an overview of published induced earthquake cases to date. Expanding on this, we synthesize the common themes and interpret the origin of these commonalities, which include recurrent earthquake swarms, proximity to well bore, rapid response to stimulation, and a paucity of reported cases. Next, we discuss the unanswered questions that naturally arise from these commonalities, leading to potential research themes: consistent recognition of cases, proposed triggering mechanisms, geologically susceptible conditions, identification of operational controls, effective mitigation efforts, and science informed regulatory management. HF-induced seismicity provides a unique opportunity to better understand and manage earthquake rupture processes; overall, understanding HF-induced earthquakes is important in order to avoid extreme reactions in either direction. |
Octubre de 2020 Offshore real time ocean bottom networks of seismometers and ocean bottom pressure (OBP) gauges have been recently established such as DONET and S‐net around the Japanese islands. One of their purposes is to practice rapid and accurate tsunami forecasting. Near‐fault OBP records, however, are always contaminated by nontsunami components such as sea‐bottom acceleration change until an earthquake stops its fault or sea floor motions. This study proposes a new method to separate tsunami and ocean bottom displacement components from coseismic OBP |
records in a real time basis. Associated with the Off Mie earthquake of 2016 April 1, we first compared OBP data with acceleration, velocity, and displacement seismograms recorded by seismometers at common ocean bottom sites in both time and frequency domains. Based on this comparison, we adopted a band‐pass filter of 0.05–0.15 Hz to remove ocean‐bottom acceleration components from the OBP data. Resulting OBP waveforms agree well with the tsunami components estimated by a 100 s low pass filter with records of several hundred seconds in length. Our method requires only an early portion of a given OBP record after 30 s of an origin time in order to estimate its tsunami component accurately. Our method enhances early tsunami detections with near‐fault OBP data; that is, it will make a tsunami forecasting system faster and more reliable than the previous detection schemes that require data away from source regions or after coseismic motions are over. |
Octubre de 2020 In this study, we investigate the possibility of using a high density fluid to induce downward fracture growth in a hydraulic fracturing process. We propose a mathematical model to calculate the minimum amount of a dense fluid required to trigger downward fracture propagation under gravity forces, and we verify the calculated minimum volume of the fluid through numerical simulations. Results show |
that when the injected fluid exceeds the minimum amount, a steady downward growth of the hydraulic fracture is obtained. The fracture propagation consists of two distinct responses: The first response can occur under either toughness dominated, viscosity dominated, or an intermediate hydraulic fracturing regime, depending on fluid rheology, rock properties, and injection scenario. The second response occurs mainly under the toughness dominated regime, meaning the predominant energy dissipation mechanism is to overcome the fracture toughness and break the rock. In the latter, the speed of the downward fracture growth depends on the viscosity and fluid weight. |
Septiembre de 2020 In December 2018, Etna volcano experienced one of the largest episodes of unrest since the installation of geophysical monitoring networks in 1970. The unrest culminated in a short eruption with a small volume of lava erupted, a significant seismic crisis and deformation of the entire volcanic edifice of magnitude never recorded before at Mount Etna. Here we describe the evolution of the 2018 eruptive cycle from the analysis of seismic and geodetic data collected in the months preceding, during, and following the intrusion. We model the space time evolution of high rate deformation data starting |
from the active source previously identified from deformation data and the propagation of seismicity in a 3 D velocity model. The intrusion model suggests emplacement of two dikes: a smaller dike located beneath the eruptive fissure and a second, deeper dike between 1 and 5 km below sea level that opened ~2 m. The rise and eruption of magma from the shallower dike did not interrupt the pressurization of a long‐lasting deeper reservoir (~6 km) that induced continuous inflation and intense deformation of the eastern flank. Shortly after the intrusion, on 26 December 2018, a ML4.8 earthquake occurred near Pisano, destroying buildings and roads in two villages. We propose a time dependent intrusion model that supports the hypothesis of the inflation inducing flank deformation and that this process has been active since September 2018. |
Septiembre de 2020 En echelon fissures 100–300 km long on Europa are found to be concentric and external to arcuate troughs previously attributed to true polar wander (TPW) of Europa's ice shell, strengthening the case for TPW. Fissures are composed of parallel faults distributed over 10‐to‐20‐km‐wide zones, with deformation focused in a main fissure 1–2 km wide |
and up to 200 m deep. Fissures crosscut all known terrains, including (apparently) ejecta of bright ray crater Manannan, establishing that fissures and by inference TPW are among the most recent geologic events on Europa. Very late ~70° of TPW shell rotation requires that most observed structures on Europa are not in their original configuration with respect to other stress regimes, requiring complete reanalysis of Europa's strain history. If reorientation happened recently, we predict that any crater distribution asymmetries and shell thickness variations measured by Europa Clipper will be offset from expected equilibrium patterns. |
Septiembre de 2020 More than 90% of the energy trapped on Earth by increasingly abundant greenhouse gases is absorbed by the ocean. Monitoring the resulting ocean warming remains a challenging sampling problem. To complement existing point measurements, we introduce a method that infers |
basin-scale deep-ocean temperature changes from the travel times of sound waves that are generated by repeating earthquakes. A first implementation of this seismic ocean thermometry constrains temperature anomalies averaged across a 3000-kilometer-long section in the equatorial East Indian Ocean with a standard error of 0.0060 kelvin. Between 2005 and 2016, we find temperature fluctuations on time scales of 12 months, 6 months, and ~10 days, and we infer a decadal warming trend that substantially exceeds previous estimates. |
Septiembre de 2020 Fractures in frozen soils (frost quakes) can cause damage to buildings and other infrastructure, but their formation mechanisms remain poorly understood. A methodology was developed to assess thermal stress on soil due to changes in climate and weather conditions and to investigate the connection between thermal stress and frost quakes in central Finland due to brittle fracturing in uppermost soils. A hydrological model was used to simulate snow accumulation and melt, and a soil . |
temperature model was used to simulate soil temperature at different depths beneath the snow pack. The results of modeling, together with measurements of air temperature, snow cover thickness, and soil temperature, were used to calculate temporal variations in thermal stress in soil. We show that frost quakes occur when thermal stress caused by a rapid decrease in temperature exceeds fracture toughness and strength of the soil‐ice mixture. We compared calculated thermal stress on soil, critical stress intensity factor, and a seismogram recorded in a suburban region in central Finland. Our results suggest that this methodology can be used to predict thermal stresses on soil and identify stress values that may lead to fractures of frozen soils, that is, frost quakes |
Septiembre de 2020 Giant earthquakes with magnitudes above 8.5 occur only in subduction zones. Despite the developments made in observing large subduction zone earthquakes with geophysical instruments, the factors controlling the maximum size of these earthquakes are still poorly understood. Previous studies have suggested the importance of slab shape, roughness of the plate interface contact, state of the strain in the upper plate, thickness of sediments filling the trenches, and subduction rate. Here, we present 2-D cross-scale numerical models of seismic cycles for subduction zones with various geometries, subduction channel friction configurations, and subduction rates. We found that low angle subduction and thick sediments in the |
subduction channel are the necessary conditions for generating giant earthquakes, while the subduction rate has a negligible effect. We suggest that these key parameters determine the maximum magnitude of a subduction earthquake by controlling the seismogenic zone width and smoothness of the subduction interface. This interpretation supports previous studies that are based upon observations and scaling laws. Our modeling results also suggest that low static friction in the sediment‐filled subduction channel results in neutral or moderate compressive deformation in the overriding plate for low‐angle subduction zones hosting giant earthquakes. These modeling results agree well with observations for the largest earthquakes. Based on our models we predict maximum magnitudes of subduction earthquakes worldwide, demonstrating the fit to magnitudes of all giant earthquakes of the 20th and 21st centuries and good agreement with the predictions based on statistical analyses of observations. |
Septiembre de 2020 Recent studies have evaluated the Coulomb stress change method, a popular technique for calculating where future earthquakes will occur, against alternative stress change representations. Spatial forecasts were compared with receiver operating characteristic tests, which rank methods based on the number of true and false positive and negative |
forecast cases. Coulomb stress changes, which predict areas of positive and negative stress change fare poorly against methods that only produce positive forecast areas. Methods that forecast negative cases (earthquake suppression) have to be nearly perfect to score well in a receiver operating characteristic test against even an informationless all positive forecast, because there are no possible false negatives. There is also a general data imbalance problem with using ROC tests for earthquake forecasts because there are almost always many more negative cases (places with no earthquakes). |
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Septiembre de 2020 The largest earthquakes in subduction zones occur where significant interseismic slip deficit has accumulated on the plate interface. Slip deficit accumulates most quickly in mechanically locked regions, and these also cause the regions around them to accumulate slip deficit; therefore, large earthquakes are typically expected to rupture in and around locked areas. The locations and dimensions of these locked zones have been difficult to resolve using standard techniques and available data sets. We develop a new statistical interseismic inversion approach that incorporates the physical interactions between nearby fault areas to directly determine the distribution of locking on the subduction plate |
interface (simultaneously with rigid forearc motions) from interseismic surface velocities. Because we include physical prior information in the inversion procedure, this approach reduces uncertainties in the rate of slip deficit accumulation, even in locations (such as near the trench) where kinematic inversions of onshore data have relatively low resolution. Applying the inversion to the South America subduction zone, we find that the pattern of locking and corresponding slip deficit rates correlate well with recent and historical large earthquake ruptures. Locked patch dimensions are <40 km and account for no more than 30% of the area of the plate interface. The small size of the imaged locked zones is a natural outcome of our physical assumptions and implies that mechanical locking is caused by correspondingly small geological features. Despite their small dimensions, locked zones generate substantial slip deficit on the surrounding plate interface, consistent with the slip patterns of large megathrust earthquakes. |
Septiembre de 2020 A dense network of ground global navigation satellite system (GNSS) receivers detected ionospheric total electron content (TEC) changes starting ~40 minutes before the 2011 Tohoku‐oki (Mw 9.0) earthquake around the ruptured fault, together with the long‐lasting postseismic TEC drop. In this paper, we robustly estimate three‐dimensional (3D) distribution of both pre‐ and post‐seismic ionospheric anomalies of the 2011 Tohoku‐oki earthquake by tomographic inversions of electron density anomalies. We set up > 6,000 blocks, as large as 1.0o (east‐west) x 0.9o (north‐south) x 60 km (vertical), over the Japanese Islands, the Sea of Japan, and the Korean Peninsula, up to 870 km altitude. By using TEC |
anomalies of pairs exceeding ~1,300 stations and 8 satellites obtained using reference curves, we estimated electron density anomalies within individual blocks. The results showed that the pre‐ and postseismic anomalies do not overlap in space. The preseismic anomalies are composed of low (~300 km height) positive and high (~600 km height) negative anomalies. They occurred above the land of NE Japan without extending offshore, suggesting its origin related to surface electric charges. On the other hand, the postseismic electron depletion occurred offshore above the region where large coseismic uplift took place. These results demonstrate that the pre‐ and postseismic ionospheric anomalies are independent not only temporarily but also spatially, and certainly in underlying physical mechanisms. We propose a simple model to explain how surface charges redistribute ionospheric electrons to make the observed preseismic electron density anomalies. |
Septiembre de 2020 We examine the relationship between earthquakes and ultralow frequency (ULF) wave activity in the nighttime ionosphere based on the electric field data in the direct current/ULF range observed by the DEMETER satellite over a ~5.5 year period from May 2005 to November 2010. ULF wave activity is identified by an automatic detection algorithm and |
those which occur on the geomagnetic disturbed days (Kp > 3 at any time intervals) are discarded. Only the earthquakes with depth ≤70 km and occurring in the region of |MLat| < 40° are selected. A superposed epoch analysis is performed to study the statistical association between ULF wave activity and the selected earthquakes. The results show that (1) there are clearly temporal and spatial correlations between ULF wave activity and earthquakes whose catalog magnitudes are both ≥4.8 and ≥5.0, and (2) enhanced ULF wave occurrence rate happens ~1 day and 1 week before the earthquakes and at less than 200 km distance from the epicenters. |
Septiembre de 2020 Groundwater discharge zones connect aquifers to surface water, generating baseflow and serving as ecosystem control points across aquatic ecosystems. The influence of groundwater discharge on surface flow connectivity, fate and transport of contaminants and nutrients, and thermal habitat depends strongly on hydrologic characteristics such as the spatial distribution, age, and depth of source groundwater flowpaths. Groundwater models have the potential to predict spatial discharge characteristics within river networks, but models are often not evaluated against these critical characteristics and model equifinality in regards to discharge processes is a known challenge. We quantify discharge characteristics across a suite of groundwater |
models with commonly used frameworks and calibration data. We developed a base model (MODFLOW‐NWT) for a 1570 km2 watershed in the northeastern United States and varied the calibration data and settings; control of river‐aquifer exchange directionality; and resolution. Most models (n = 11 of 12) fit similarly to calibration metrics, but patterns in discharge location, flowpath depth, and subsurface travel time varied substantially. We found 1) a 15% difference in the percent of discharge going to 1st order streams, 2) three‐fold variations in flowpath depth, and 3) seven‐fold variations in the subsurface travel times. We recalibrated three models using a synthetic discharge location dataset. Calibration with discharge location data reduced differences in simulated discharge characteristics, suggesting an approach to reduced equifinality based on widespread field‐based mapping of discharge zones. Our work quantifying variation across common modeling approaches is an important step toward characterizing and improving predictions of groundwater discharge characteristics. |
Agosto de 2020 The differential motion between the lithosphere and the asthenosphere is aseismic, so the magnetotelluric (MT) method plays an important role in studying the depth and nature of the lithosphere‐asthenosphere boundary (LAB). In March 2016, we deployed 39 marine MT instruments across the Middle Atlantic Ridge (MAR), 2000 km away from the African coast, to study the evolution of the LAB with ages out to 45 million years (My). The MT acquisition time was limited to about 60 days by battery life. After analyzing dimensionality and coast effects for the MT data, determinant data were |
inverted for two‐dimensional resistivity models .along two profiles north and south of the Chain Fracture Zone (CFZ). The imaged thickness of the lithospheric lid (> 100 Ωm) ranges from 20 to 80 km, generally thickening with age. In the north of CFZ, punctuated low resistivity anomalies (< 1 Ωm), likely associated with potential partial melts, occur along its base. In the south of CFZ, the base of the resistive lid is demarcated by a low resistivity channel (< 1 Ωm) most likely fed by deeper melts. Sensitivity analyses and structural recovery tests indicate the robustness of these features. Resistivity models are in good agreement with results of seismic data. These results imply that partial melt is persistent over geologic timescales and that the LAB is dynamic features fed by upward percolation of mantle melt. The melt fraction is about 1‐7% based on the resistivity, temperature, pressure, and hydrous basalt models, which is consistent with petrophysical observations. |
Agosto de 2020 In June 2019, an earthquake sequence comprising five M > 5 events occurred in a region of southwest China with fluid injection for both hydraulic fracturing and salt mining, which raised an extensive controversy on the cause. Here we use interferometric synthetic aperture radar (InSAR) observations to determine the source parameters of the sequence and to investigate the relationship |
with local injection activities. Both Sentinel‐1 and Advanced Land Observing Satellite 2 SAR images are collected to measure coseismic and preseismic surface deformation. Geodetic inversions with coseismic observations show that the sequence ruptured a previously unmapped southwest‐dipping thrust fault above 3 km depth, which intersects with the open‐hole sections of wells for solution mining of salt. In the 4 months before the sequence, cumulative line‐of‐sight displacements near the wells are around 1–2 cm after correcting seasonal‐like deformation. Our results indicate that water injection likely enhanced pore pressure within the fault zone and thus contributed to inducing the sequence. |
Agosto de 2020 Asperities are patches where the fault surfaces stick until they break in earthquakes. Locating asperities and understanding their causes in subduction zones is challenging because they are generally located offshore. We use seismicity, interseismic and coseismic slip, and the residual gravity field to |
map the asperity responsible for the 2014 M8.1 Iquique, Chile, earthquake. For several years prior to the mainshock, seismicity occurred exclusively downdip of the asperity. Two weeks before the mainshock, a series of foreshocks first broke the upper plate then the updip rim of the asperity. This seismicity formed a ring around the slip patch (asperity) that later ruptured in the mainshock. The asperity correlated both with high interseismic locking and a circular gravity low, suggesting that it is controlled by geologic structure. Most features of the spatiotemporal seismicity pattern can be explained by a mechanical model in which a single asperity is stressed by relative plate motion. |
Agosto de 2020 Earthquake moment tensors in eastern Pacific (ePac) slabs typically show downdip tensional (DT) axes, whereas in the western Pacific (wPac), they typically show downdip compressional (DC) axes or have mixed orientations indicative of unbending. Prevailing conceptual models emphasize uniform stress/deformation modes, that is, bulk slab stretching or shortening, as the dominant control on intermediate depth seismic expression. In contrast, we propose that a diversity of seismic expression, including DT and DC dominated regions, is consistent with expectations of flexural strain accumulation, based on systemic differences in |
slab geometry. Our analysis reveals two largely unrecognized features of ePac intraslab seismicity. First, earthquake clusters consistent with slab unbending are present in ePac slabs, albeit at much shallower depths than typical of wPac slabs. Second, intermediate depth ePac DT seismicity is strongly localized to the upper half of zones undergoing curvature increase, such as flat slab segments. Our study highlights how the seismic expression of slab flexure is impacted by the relative contribution of brittle and ductile deformation. The strongly asymmetric temperature structure that is preserved in sinking slabs means that seismicity disproportionately records the deformation regime in the colder part of the slab, above the neutral plane of bending. The expression of in‐plane stress may be discernible in terms of a systematic modifying effect on the seismic expression of flexure. |
Agosto de 2020 Spatial forecasts of triggered earthquake distributions have been ranked using receiver operating characteristic (ROC) tests. The test is a binary comparison between regions of positive and negative forecast against positive and negative presence of earthquakes. Forecasts predicting only positive changes score higher than Coulomb methods, which predict positive and negative |
changes. I hypothesize that removing the possibility of failures in negative forecast realms yields better ROC scores. I create a ‘perfect’ Coulomb forecast where all earthquakes only fall into positive stress change areas and compare with an informationless all‐positive forecast. The ‘perfect’ Coulomb forecast barely beats the informationless forecast, and adding as few as 4 earthquakes occurring in the negative stress regions causes the Coulomb forecast to be no better than an informationless forecast under a ROC test. ROC tests also suffer from data imbalance when applied to earthquake forecasts because there are many more negative cases than positive. |
Julio de 2020 Injection of fluids in geo‐reservoirs can reduce the effective stresses at depth, lubricating the nearby faults, promoting slip and, potentially, earthquakes. High‐viscous fluids are often used during hydraulic fracturing and production phases in geo‐reservoirs. Here, we performed dedicated experiments to study the influence of fluid viscosity on earthquake nucleation. We performed frictional sliding |
experiments at 30 and 50 effective normal stresses and fluids viscosity ranging from 1 to 1,226 mPa s and modeled them with a rate‐and‐state friction law. In the presence of fluid, the state variable is defined as the ability of the fluid to flow. Our results showed that static friction slightly decreases with increasing viscosity, the dynamic friction is governed by the dimensionless Sommerfeld number (S = 6ηVL /(σ 'n H 2)). Moreover, we observed that the (a − b ) parameters of the rate‐and‐state friction law decrease with increasing viscosity down to (a − b ) < 0, possibly promoting unstable slip and earthquake nucleation. |
Julio de 2020 Hydraulic fracturing (HF) is a technique that is used for extracting petroleum resources from impermeable host rocks. In this process, fluid injected under high pressure causes fractures to propagate. This technique has been transformative for the hydrocarbon industry, unlocking otherwise stranded resources; however, environmental concerns make HF controversial. One concern is HF‐induced seismicity, since fluids driven under high pressure also have the potential to reactivate faults. Controversy has inevitably followed these HF‐induced earthquakes, with economic and human losses from ground shaking at one extreme and moratoriums on resource development at the other. Here, we review the state of knowledge of this |
category of induced seismicity. We first cover essential background information on HF along with an overview of published induced earthquake cases to date. Expanding on this, we synthesize the common themes and interpret the origin of these commonalities, which include recurrent earthquake swarms, proximity to well bore, rapid response to stimulation, and a paucity of reported cases. Next, we discuss the unanswered questions that naturally arise from these commonalities, leading to potential research themes: consistent recognition of cases, proposed triggering mechanisms, geologically susceptible conditions, identification of operational controls, effective mitigation efforts, and science‐informed regulatory management. HF‐induced seismicity provides a unique opportunity to better understand and manage earthquake rupture processes; overall, understanding HF-induced earthquakes is important in order to avoid extreme reactions in either direction. |
Julio de 2020 Phase alignment (synchronization) is a generalized property of interacting oscillators. If such interactions apply to earthquakes, they should manifest as time‐dependent variations in earthquake productivity organized according to a characteristic elastic loading period. Defining this period as renewal interval, the time required to accumulate the elastic potential energy released in a rupture, gives |
a consistent scaling property that can be used to search for temporal organization. We test for the expected structure in earthquake productivity using three different statistical tools optimized for different temporal sensitivities: Schuster spectra for events with short renewal intervals (0–25 years), Fourier power spectra for events with short and intermediate renewal intervals (0–100 years), and topological data analysis (TDA) for events with long renewal intervals (>100 years). All three indicate that earthquakes are organized in time according to renewal interval. Accounting for such unsteady temporal organization may improve forecasting skill by providing time-dependent event probabilities. |
Junio de 2020 Scattering of seismic waves can reveal subsurface structures but usually in a piecemeal way focused on specific target areas. We used a manifold learning algorithm called “the Sequencer” to simultaneously analyze thousands of seismograms of waves diffracting along the core-mantle boundary and obtain a panoptic view of scattering across the |
Pacific region. In nearly half of the diffracting waveforms, we detected seismic waves scattered by three-dimensional structures near the core-mantle boundary. The prevalence of these scattered arrivals shows that the region hosts pervasive lateral heterogeneity. Our analysis revealed loud signals due to a plume root beneath Hawaii and a previously unrecognized ultralow-velocity zone beneath the Marquesas Islands. These observations illustrate how approaches flexible enough to detect robust patterns with little to no user supervision can reveal distinctive insights into the deep Earth. |
Junio de 2020 The vibrant evolutionary patterns made by earthquake swarms are incompatible with standard, effectively two-dimensional (2D) models for general fault architecture. We leverage advances in earthquake monitoring with a deep-learning The vibrant evolutionary patterns made by earthquake swarms are incompatible with standard, effectively two-dimensional (2D) models for general fault architecture. We leverage advances in earthquake |
monitoring with a deep-learning algorithm to image a fault zone hosting a 4-year-long swarm in southern California. We infer that fluids are naturally injected into the fault zone from below and diffuse through strike-parallel channels while triggering earthquakes. A permeability barrier initially limits up-dip swarm migration but ultimately is circumvented. This enables fluid migration within a shallower section of the fault with fundamentally different mechanical properties. Our observations provide high-resolution constraints on the processes by which swarms initiate, grow, and arrest. These findings illustrate how swarm evolution is strongly controlled by 3D variations in fault architecture. |
Junio de 2020 Deep within Earth's interior, at ∼2900 km beneath the surface, lies the boundary between the solid silicate rock mantle and the liquid iron-nickel alloy core (the core-mantle boundary). Geophysicists have studied the complex thermal and chemical dynamics that take place in this boundary layer. In |
the early 20th century, Gutenberg investigated the structure of the lowermost region, or base, of the mantle by recording with only a few seismograms from a small number of large-magnitude earthquakes that occurred thousands of kilometers away (1). The structure of the rocks just above the core-mantle boundary—designated as D″ by Jeffreys in 1939 (2)—forms a distinct layer with surprising complexity. Now, on page 1223 of this issue, Kim et al. (3) describe new structural heterogeneities in the lowermost mantle with the use of a learning algorithm that does not require any a priori knowledge of Earth. |
Mayo de 2020 Data assimilation allows for updating state variables in a model to represent the initial condition of a catchment more accurately than the initial Open Loop simulation. In hydrology, data assimilation is often a pre requisite for forecasting. According to Hornik [1991], artificial neural networks can learn any nonlinear relationship between inputs and outputs. Here, we hypothesize that neural networks could learn the relationship between the simulated streamflow (from a hydrological model) and the corresponding state variables. Once learned, this relationship can be used to obtain corrected state |
variables by applying it to observed rather than simulated streamflow. Based on this, we propose a novel, ensemble based, data assimilation approach. As a proof of concept and to verify the above mentioned hypothesis, we used an international testbed comprising four hydrologically dissimilar catchments. We applied the new data assimilation method to the lumped hydrological model GR4J, which has two state variables. Within this framework, we compared two types of neural networks, namely Extreme Learning Machine and the Multilayer Perceptron. Using well known metrics such as the Continuous Ranked Probability Score, we compared the assimilated streamflow series with the Open Loop streamflow series and with the observed streamflow. We show that neural networks can be successfully used for data assimilation, with a noticeable improvement over the Open Loop simulation for all catchments |
Mayo de 2020 The paper investigates the applicability of machine learning (ML) to weather prediction by building a reservoir computing‐based, low‐resolution, global prediction model. The model is designed to take advantage of the massively parallel architecture of a modern supercomputer. The forecast performance of the model is assessed by comparing it to that of |
daily climatology, persistence, and a numerical (physics based) model of identical prognostic state variables and resolution. Hourly resolution 20‐day forecasts with the model predict realistic values of the atmospheric state variables at all forecast times for the entire globe. The ML model outperforms both climatology and persistence for the first three forecast days in the midlatitudes, but not in the tropics. Compared to the numerical model, the ML model performs best for the state variables most affected by parameterized processes in the numerical model. |
Mayo de 2020 A systematic scan of seismic waveform archives on the Island of Hawai'i has revealed subtle but persistent near-periodic pulses originating within the deep magma plumbing system of Mauna Kea, a |
dormant volcano that last erupted 4500 years ago. On page 775 of this issue, Wech et al. (1) report the detection of over a million of the deep (22 to 25 km below sea level) long-period seismic events, which have been occurring continuously and repetitively, often with precise regularity (every 7 to 12 min), for at least 18 years. This discovery offers new views into the origin of this mysterious type of deep volcanic seismicity. |
Abril de 2020 Large earthquakes are the product of elastic stress that has accumulated over decades to centuries along segments of active faults. Assuming an elastic crust, one can roughly estimate the location and rate of accumulation of elastic stress. However, this general framework does not account for inelastic, irrecoverable deformation, which results in |
large scale topography. We do not know over which part of the earthquake cycle such deformation occurs. Using InSAR and GNSS measurements, we report on a potential correlation between long term, inelastic vertical rate and short erm, interseismic vertical rate in northern Chile. Approximately 4% to 8% of the geodetically derived interseismic vertical rates translate into permanent deformation, suggesting that topography of the forearc builds up during the interseismic period. This observation provides a quantitative basis for an improved understanding of the interplay between short‐term and long term dynamics along convergent plate boundaries. |
Abril de 2020 Watersheds have served as one of our most basic units of organization in hydrology for over 300 years. With growing interest in groundwater surface water interactions and subsurface flow paths, hydrologists are increasingly looking deeper. But the dialog between surface water hydrologists and groundwater hydrologists is still embryonic, and many basic questions are yet to be posed, let alone answered. One key question is: where is the bottom of a watershed? Knowing where to draw the bottom boundary has not yet been fully addressed in the literature, and how to define the watershed “bottom” |
is a fraught question. There is large variability across physical and conceptual models regarding how to implement a watershed bottom, and what counts as “deep” varies markedly in different communities. In this commentary, we seek to initiate a dialog on existing approaches to defining the bottom of the watershed. We briefly review the current literature describing how different communities typically frame the answer of just how deep we should look and identify situations where deep flow paths are key to developing realistic conceptual models of watershed systems. We then review the common conceptual approaches used to delineate the watershed lower boundary. Finally, we highlight opportunities to trigger this potential research area at the interface of catchment hydrology and hydrogeology. |
Marzo de 2020 Slow earthquakes may trigger failure on neighboring locked faults that are stressed sufficiently to break, and slow slip patterns may evolve before a nearby great earthquake. However, even in the clearest cases such as Cascadia, slow earthquakes and associated tremor have only been observed in |
intermittent and discrete bursts. By training a convolutional neural network to detect known tremor on a single seismic station in Cascadia, we isolate and identify tremor and slip preceding and following known larger slow events. The deep neural network can be used for the detection of quasi continuous tremor, providing a proxy that quantifies the slow slip rate. Furthermore, the model trained in Cascadia recognizes tremor in other subduction zones and also along the San Andreas Fault at Parkfield, suggesting a universality of waveform characteristics and source processes, as posited from experiments and theory. |
Marzo de 2020 Data assimilation allows for updating state variables in a model to represent the initial condition of a catchment more accurately than the initial Open Loop simulation. In hydrology, data assimilation is often a pre-requisite for forecasting. According to Hornik [1991], artificial neural networks can learn any nonlinear relationship between inputs and outputs. Here, we hypothesize that neural networks could learn the relationship between the simulated streamflow (from a hydrological model) and the corresponding state variables. Once learned, this relationship can be used to obtain corrected state |
variables by applying it to observed rather than simulated streamflow. Based on this, we propose a novel, ensemble based, data assimilation approach. As a proof of concept and to verify the above mentioned hypothesis, we used an international testbed comprising four hydrologically dissimilar catchments. We applied the new data assimilation method to the lumped hydrological model GR4J, which has two state variables. Within this framework, we compared two types of neural networks, namely Extreme Learning Machine and the Multilayer Perceptron. Using well known metrics such as the Continuous Ranked Probability Score, we compared the assimilated streamflow series with the Open Loop streamflow series and with the observed streamflow. We show that neural networks can be successfully used for data assimilation, with a noticeable improvement over the Open Loop simulation for all catchments. |
Marzo de 2020 Geophysicists depend on rock physics relationships to interpret resistivity and seismic velocity in terms of rock porosity, but it has proven difficult to capture the effect of pore geometry on such relations through simple and easy to apply formulae. Inclusion modeling relates moduli to porosity through an equivalent grain or pore aspect ratio but often fails to account for observed trends, whereas empirical relations can be hard to extrapolate beyond their range of validity, often giving incorrect results in the |
low and high porosity limits. We show that introducing a power-law relationship between porosity and equivalent grain or pore aspect ratio allows inclusion models to reproduce 5 published empirical resistivity-porosity and velocity‐porosity relationships, providing a first principles basis for extrapolation to other cases of interest. We find the deviation of resistivity from Archie's law in carbonates is related to a systematic change of grain shape with porosity, and we derive a new relation which fits carbonate resistivity data with similar accuracy to the Humble equation while being correct at high porosity. We then obtain an analog for the Castagna and Pickett relationships for wet, calcitic rocks, which is valid in the low and high porosity limits, giving rise to a new, physically derived Vp/Vs versus porosity model. |
Marzo de 2020 In recent decades, a striking number of countries have suffered from consecutive disasters: events whose impacts overlap both spatially and temporally, while recovery is still under way. The risk of consecutive disasters will increase due to growing exposure, the interconnectedness of human society, and the increased frequency and intensity of nontectonic hazard. This paper provides an overview of the different types of consecutive disasters, their causes, and impacts. The impacts |
can be distinctly different from disasters occurring in isolation (both spatially and temporally) from other disasters, noting that full isolation never occurs. We use existing empirical disaster databases to show the global probabilistic occurrence for selected hazard types. Current state of the art risk assessment models and their outputs do not allow for a thorough representation and analysis of consecutive disasters. This is mainly due to the many challenges that are introduced by addressing and combining hazards of different nature, and accounting for their interactions and dynamics. Disaster risk management needs to be more holistic and codesigned between researchers, policy makers, first responders, and companies. |
Marzo de 2020 Two major reports assessing global systemic risks have been published recently, presenting large scale panel data on the risk perceptions of different key communities, most notably business leaders |
and global change scientists. While both of these global communities agree on ranking environmental risks the highest, followed by societal, geopolitical, technological, and economic risks, business leaders perceive the likelihood of most risks as lower than scientists. This gap implies vexing questions in relation to building a shared sense of urgency and facilitating collective action. These questions need to be addressed through new ways of co creating risk assessments and strategic futures analysis. |
Marzo de 2020 We use a machine learning approach to build a ground motion model (GMM) from a synthetic database of ground motions extracted from the Southern California CyberShake study. An artificial neural network is used to find the optimal weights that best fit the target data (without overfitting), with input parameters chosen to match that of state of |
the art GMMs. We validate our synthetic based GMM with empirically based GMMs derived from the globally based Next Generation Attenuation West2 data set, finding near zero median residuals and similar amplitude and trends (with period) of total variability. Additionally, we find that the artificial neural network GMM has similar bias and variability to empirical GMMs from records of the recent Ridgecrest event, which neither GMM has included in its formulation. As simulations continue to better model broadband ground motions, machine learning provides a way to utilize the vast amount of synthetically generated data and guide future parameterization of GMMs |
Marzo de 2020 Seismic hazard modeling is a multidisciplinary science that aims to forecast earthquake occurrence and its resultant ground shaking. Such models consist of a probabilistic framework that quantifies uncertainty across a complex system; typically, this includes at least two model components developed from Earth science: seismic source and ground motion models. Although there is no scientific prescription for the forecast length, the most common probabilistic seismic hazard analyses consider forecasting windows of 30 to 50 years, which are typically an engineering demand for building code purposes. These types of analyses are the topic of this review paper. Although the core |
methods and assumptions of seismic hazard modelling have largely remained unchanged for more than 50 years, we review the most recent initiatives which face the difficult task of meeting both the increasingly sophisticated demands of society and keeping pace with advances in scientific understanding. A need for more accurate and spatially precise hazard forecasting must be balanced with increased quantification of uncertainty and new challenges such as moving from time independent hazard to forecasts that are time dependent and specific to the time period of interest. Meeting these challenges requires the development of science‐driven models which integrate all information available, the adoption of proper mathematical frameworks to quantify the different types of uncertainties in the hazard model, and the development of a proper testing phase of the model to quantify its consistency and skill. We review the state of the art of the national seismic hazard modeling, and how the most innovative approaches try to address future challenges. |
Marzo de 2020 Fluid overpressure is a primary mechanism behind fault interaction and earthquakes triggering. The Apennines section within the young Alpine mobile belt is a key locus to investigate the interplay between fluids and faults. Here, seismicity develops along the extending mountain belt and the key role of fluids has been invoked in past large earthquake sequences. In this study, we use seismological data to get improved images of the Apennines |
normal faulting system, trying to catch evidences for the involvement of fluids in the preparatory phase of large earthquakes. We observe that extension preferentially reutilizes inherited fragments of faults which were assembled during the Mio Pliocene contraction, with steep segments that floor on a regional scale gently east dipping plane. We find evidences for wide volumes of over pressured fluids at the base of the seismogenic layer, which are connected to the activation of the recent large earthquakes. The recognition of fluids compartments with over pressuring and diffusion moulding seismicity is a key to understand faulting processes and possibly develop forecasts scenarios. |
Marzo de 2020 Entropy and Information are key concepts not only in Information Theory but also in Physics: historically in the fields of Thermodynamics, Statistical and Analytical Mechanics, and, more recently, in the field of Information Physics. In this paper we argue that Information Physics reconciles and generalizes statistical, geometric, and mechanistic views on information. We start by demonstrating how the use and interpretation of Entropy and Information |
coincide in Information Theory, Statistical Thermodynamics, and Analytical Mechanics, and how this can be taken advantage of when addressing Earth Science problems in general and hydrological problems in particular. In the second part we discuss how Information Physics provides ways to quantify Information and Entropy from fundamental physical principles. This extends their use to cases where the preconditions to calculate Entropy in the classical manner as an aggregate statistical measure are not met. Indeed, these preconditions are rarely met in the Earth Sciences due either to limited observations or the far from equilibrium nature of evolving systems. Information Physics therefore offers new opportunities for improving the treatment of Earth Science problems. |
Marzo de 2020 The rheology of oceanic lithosphere is important to our understanding of mantle dynamics and to the emergence and manifestations of plate tectonics. Data from experimental rock mechanics suggest rheology is dominated by three different deformation mechanisms including frictional sliding, low temperature plasticity, and high temperature creep, from shallow depths at relatively cold temperatures to large depths at relatively high temperatures. However, low temperature plasticity is poorly understood. This study further constrains low‐temperature plasticity by comparing observations of flexure at the Hawaiian Islands to predictions from 3 D viscoelastic loading models with a realistic lithospheric rheology of frictional sliding, low temperature plasticity, and . |
high temperature creep. We find that previously untested flow laws significantly underpredict the amplitude and overpredict the wavelength of flexure at Hawaii. These flow laws can, however, reproduce observations if they are weakened by a modest reduction (25–40%) in the plastic activation energy Lithospheric rheology is strongly temperature dependent, and so we explore uncertainties in the thermal structure with different conductive cooling models and convection simulations of plume‐lithosphere interactions. Convection simulations show that thermal erosion from a plume only perturbs the lithospheric temperature significantly at large depths so that when it is added to the thermal structure, it produces a small increase in deflection. In addition, defining the temperature profile by the cooling plate model produces only modest weakening relative to the cooling half space model. Therefore, variation of the thermal structure does not appear to be a viable means of bringing laborator ‐derived flow laws for low temperature plasticity into agreement with geophysical field observations and modeling. |
Marzo de 2020 In this study, we present a fast and reliable method for end to end estimation of earthquake magnitude from raw waveforms recorded at single. stations. We design a regressor (MagNet) composed of convolutional and recurrent neural networks that is not sensitive to the data normalization, hence waveform amplitude |
information can be utilized during the training. The network can learn distance dependent and site‐dependent functions directly from the training data. Our model can predict local magnitudes with an average error close to zero and standard deviation of ~0.2 based on single station waveforms without instrument response correction. We test the network for both local and duration magnitude scales and show a station based learning can be an effective approach for improving the performance. The proposed approach has a variety of potential applications from routine earthquake monitoring to early warning systems |
Febrero de 2020 In order to quantify the optimal radiation shielding depth on Mars in preparation for future human habitats on the red planet, it is important to understand the Martian radiation environment and its dependence on the planetary atmospheric and geological properties. With this motivation we calculate the absorbed dose and equivalent dose rates induced by Galactic Cosmic Ray (GCR) particles at varying heights above and below the Martian surface considering various subsurface compositions (ranging from dry rock to water rich regolith). The state of the art Atmospheric Radiation Interaction Simulator (AtRIS) based on GEANT4 (GEometry And Tracking) Monte Carlo method has |
been employed for simulating particle interaction with the Martian atmosphere as well as subsurface materials. We calculate the absorbed dose in two different phantoms: a thin silicon slab and a water sphere. The former is used to validate our model against the surface measurement by the Radiation Assessment Detector on the Curiosity rover while the later is used to approximate a human torso, also for evaluation the biologically weighted equivalent dose. We find that the amount of hydrogen contained in the water rich regolith is playing an important role in reducing the equivalent dose through modulation of neutron flux (below 10 MeV). This effective shielding by underground water is also present above the surface, providing an indirect shielding for potential human explorations at this region. For long term habitats seeking the Martian natural surface material as protection, we also estimate the optimal shielding depth, for different given subsurface compositions, under maximum, average and minimum heliospheric modulation conditions. |
Febrero de 2020 Paleomagnetic records from sediments, archeological artifacts, and lava flows provide the foundation for studying geomagnetic field changes over 0–100 ka. Late Quaternary time-varying spherical harmonic models for 0–100 ka produce a global view used to evaluate new data records, study the paleomagnetic secular variation on centennial to multimillennial timescales, and investigate extreme regional or global events such as the Laschamp geomagnetic excursion. Recent modeling results (GGF100k and LSMOD.2) are compared to previous studies based on regional or global stacks and averages of relative geomagnetic paleointensity variations. Time-averaged field structure is similar on Holocene, 100 ky, and |
million-year timescales. Paleosecular variation activity varies greatly over 0–100 ka, with large changes in field strength and significant morphological changes that are especially evident when field strength is low. GGF100k exhibits a factor of 4 variation in geomagnetic axial dipole moment, and higher-resolution models suggest that much larger changes are likely during global excursions. There is some suggestion of recurrent field states resembling the present-day South Atlantic Anomaly, but these are not linked to initiation or evolution of excursions. Several properties used to characterize numerical dynamo simulations as “Earth-like” are evaluated and, in future, improved models may yet reveal systematic changes linked to the onset of geomagnetic excursions. Modeling results are useful in applications ranging from ground truth and data assimilation in geodynamo simulations to providing geochronological constraints and modeling the influence of geomagnetic variations on cosmogenic isotope production rates. |
Febrero de 2020 Evolution of fault strength during the initial stages of seismic slip plays an important role in the onset of velocity-induced weakening, which in turn, leads to larger earthquake events. A key dynamic weakening mechanism during the early stages of slip is flash heating, where stress concentrations at contacts on the interface lead to the rapid generation of heat. Although potential weakening from flash heating has been extensively modeled, there is little recorded microstructural evidence of its physical manifestations. We present results of a series of triaxial experiments on synthetic faults in quartz sandstone. Samples were subjected to a variety of normal stresses and ambient temperatures, to |
induce a range of slip event sizes and sliding velocities. We show the microstructural evolution of asperity interactions from the onset of flash heating through to the formation of grain-scale areas of sheared melt. Using microstructural observations and mechanical data from the experiments, we model temperature and the viscoelastic behavior of the glass. Results suggest that, in the earliest stages of slip asperity contacts melt, but temperatures remain too low for viscous shear to occur within the melt layer. Instead melted asperities behave as glassy solids, facilitating continued frictional heating. With further slip, increased asperity temperatures allow the transition to viscous shear within the melt layer, facilitating weakening. These results highlight the dynamic evolution of the viscoelastic properties of the melt and resulting effects on asperity strength. Such complexity has, to-date, not been fully addressed in modeling of flash heating. |
Diciembre de 2019 Earthquakes are complex and diverse, ranging from energetic and destructive megathrust earthquakes to slow earthquakes. Complex earthquake rupture processes are generally modeled by prescribing a deterministic system and solving deterministic differential equations. However, such approaches cannot adequately capture the temporal evolution of a complex fault system because of the inherent |
unpredictability that results from various unprescribed processes. Such unpredictability may be better represented by time-dependent stochastic fluctuations in addition to the deterministic estimates. Here, we demonstrate that the consideration of time-dependent stochastic stress fluctuations in ordinary crack simulations can reproduce a variety of ruptures, including both crack-like and pulse-like ordinary (fast) earthquakes and slow earthquakes, by simply changing the strength drop and the initial stress level. The results indicate that stochasticity is effective for reproducing and better understanding the diversity of earthquakes, including slow earthquakes. |
Diciembre de 2019 Understanding the dominant physical processes that cause fault reactivation due to fluid injection is vital to develop strategies to avoid and mitigate injection-induced seismicity (IIS). IIS is a risk for several industries, including hydraulic fracturing, geothermal stimulation, oilfield waste disposal and carbon capture and storage, with hydraulic fracturing having been associated with some of the highest magnitude induced earthquakes (M > 5). As such, strict regulatory schemes have been implemented globally to limit the felt seismicity associated with operations. In the UK, a very strict ``traffic light” system is currently in place. These procedures were employed several times during injection at the PNR- |
1z well at Preston New Road, Lancashire, UK from October to December 2018. As injection proceeded, it became apparent to the operator that stages were interacting with a seismogenic planar structure, interpreted as a fault zone, with several ML > 0.5 events occurring. Microseismicity was clustered along this planar structure in a fashion that could not readily be explained through pore pressure diffusion or hydraulic fracture growth. Instead, we investigate the role of static elastic stress transfer created by the tensile opening of hydraulic fractures. We find that the spatial distributions of microseismicity are strongly correlated with areas that receive positive Mohr-Coulomb stress changes from the tensile fracture opening, while areas that receive negative Mohr-Coulomb stress change are quiescent. We conclude that the stressing due to tensile hydraulic fracture opening plays a significant role in controlling the spatiotemporal distribution of induced seismicity. |
Diciembre de 2019 In this study, we present a fast and reliable method for end-to-end estimation of earthquake magnitude from raw waveforms recorded at single stations. We design a regressor (MagNet) composed of convolutional and recurrent neural networks that is not sensitive to the data normalization, hence |
waveform amplitude information can be utilized during the training. The network can learn distance-dependent and site-dependent functions directly from the training data. Our model can predict local magnitudes with an average error close to zero and standard deviation of ~0.2 based on single-station waveforms without instrument response correction. We test the network for both local and duration magnitude scales and show a station-based learning can be an effective approach for improving the performance. The proposed approach has a variety of potential applications from routine earthquake monitoring to early warning systems. |
Diciembre de 2019 Airy isostasy is a concept based on simple application of Archimedes' principle, which is broadly used in solid Earth geophysics and planetary science to explain the relationship between crustal thickness variations and topography. However, the application of Airy isostasy to icy bodies is problematic due to large variations in ice viscosity and phase transitions occurring in the interior. Recently, several researchers have questioned the validity of the traditional approach to . Airy isostasy and proposed alternative approaches. |
Here we examine the accuracy of these approaches by comparing their results with those obtained from the numerical solution of the equations governing the flow in the crust of a small icy moon with a subsurface ocean. The results of our modeling suggest that the traditional approach to Airy isostasy provides a satisfactory estimate of crustal thickness variations on large spatial scales. The alternative approach based on the deviatoric stress minimization gives correct results for isoviscous model, but its accuracy deteriorates as the viscosity contrast increases. The other alternative approach, in which the deviatoric stress is neglected, is significantly less accurate than the other methods, leading to biased results for models with a thick crust. |
Diciembre de 2019 The Laguna del Maule volcanic field is a large rhyolitic magmatic system in the Chilean Andes, which has exhibited frequent eruptions during the past 20 ka. Rapid surface uplift (>20 cm/year) has been observed since 2007 accompanied by localized earthquake swarms and microgravity changes, indicating the inflating magma reservoir may interact with a preexisting weak zone (i.e., Troncoso fault). In this investigation, we model the magma reservoir by data assimilation with Interferometric Synthetic Aperture Radar data. The reservoir geometry is comparable to the magma |
body inferred by seismic tomography, magnetotelluric, and gravity studies. The models also suggest that a weak zone, which has little effect on surface displacement, is important as a fluid transport channel to promote earthquakes and microgravity changes. In particular, concentrated dilatancy within the weak zone facilitates the microfracture formation during reservoir inflation. High- pressure fluid can inject into the weak zone from the magma reservoir to trigger earthquakes and further migrate upward to create positive gravity changes by occupying unsaturated storages. The pore pressure will then decrease, halting the seismicity swarm until the next cycle. This “hydrofracturing” process may release some accumulated stress along the magma reservoir delaying an eventual eruption in turn. Besides, the resultant models are propagated forward in time to evaluate potential stress trajectories for future unrest. |
Diciembre de 2019 Giant impacts dominate the final stages of terrestrial planet formation and set the configuration and compositions of the final system of planets. A giant impact is believed to be responsible for the formation of Earth's Moon, but the specific impact parameters are under debate. Because the canonical Moon‐forming impact is the most intensely studied scenario, it is often considered the archetypal giant impact. However, a wide range of impacts with different outcomes are possible. Here we examine the total energy budgets of giant impacts that form Earth‐mass bodies and find that they differ substantially across the wide range of possible Moon‐forming events. We show that gravitational potential energy exchange is important, |
and we determine the regime in which potential energy has a significant effect on the collision outcome. Energy is deposited heterogeneously within the colliding planets, increasing their internal energies, and portions of each body attain sufficient entropy for vaporization. After gravitational re‐equilibration, post‐impact bodies are strongly thermally stratified, with varying amounts of vaporized and supercritical mantle. The canonical Moon‐forming impact is a relatively low energy event and should not be considered the archetype of accretionary giant impacts that form Earth‐mass planets. After a giant impact, bodies are significantly inflated in size compared to condensed planets of the same mass, and there are substantial differences in the magnitudes of their potential, kinetic and internal energy components. As a result, the conditions for metal‐silicate equilibration and the subsequent evolution of the planet may vary widely between different impact scenarios. |
Diciembre de 2019 Mars lacks an internally generated magnetic field today. Crustal remanent magnetism and meteorites indicate that a dynamo existed after accretion but died roughly four billion years ago. Standard models rely on core/mantle heat flow dropping below the adiabatic limit for thermal convection in the core. However, rapid core cooling after the Noachian is favored instead to produce long‐lived mantle plumes and magmatism at volcanic provinces such as Tharsis and Elysium. Hydrogenation of the core could resolve this apparent contradiction by impeding the dynamo while core/mantle heat flow is superadiabatic. Here we present parameterized |
models for the rate at which mantle convectiontdelivers hydrogen into the core. Our models sugges that most of the water that the mantle initially contained was effectively lost to the core. We predict that the mantle became increasingly ironrich over time and a stratified layer awaits detection in the uppermost core—analogous to the E′ layer atop Earth's core but likely thicker than alternative sources of stratification in the Martian core such as iron snow. Entraining buoyant, hydrogen‐rich fluid downward in the core subtracts gravitational energy from the total dissipation budget for the dynamo. The calculated fluxes of hydrogen are high enough to potentially reduce the lifetime of the dynamo by several hundred million years or longer relative to conventional model predictions. Future work should address the complicated interactions between the stratified, hydrogen-rich layer and convection in the underlying core. |
Diciembre de 2019 Discriminating between various types of seismic events is of significant scientific and societal importance. We use a machine learning method employing support vector machine (SVM) to classify tectonic earthquakes (TEs), quarry blasts (QBs) and induced earthquakes (IEs) among 30,181 1.5 < ML <2.9 seismic events that occurred in the Tianshan orogenic belt in China from 2009 to 2017. SVM classifiers are derived based on discriminant features of a training dataset consisting of 1,400 TEs selected from the aftershock sequences of 18 ML≥5.0 earthquakes, 2,881 QBs from repeating near oil and gas fields and water reservoirs. We reevaluate b values in the region and obtain relatively uniform values for the classified TEs with |
most of them below 1.0, as opposed to a large range of values (0.5‐2.7) when all the seismic events are used in the analysis.events occurring in those areas with a percentage of event daytime occurrence greater than 0.9, and 987 IEs from events in the known oil/gas fields and water reservoirs. The discriminant features include spectral amplitudes of observed P and S wave signals in a frequency range of 1‐15 Hz normalized by the P spectrum and averaged over the entire seismic network, and an optional feature of the percentage of event daytime occurrence. Statistics analyses indicate that the accuracies of the SVM classifiers are 99.81% for TEs, 99.93% for QBs and 99.62% for IEs. Our classification indicates that 37.57% of the seismic events are QBs occurring in possible mine areas and appearing mostly as clusters with a percentage of event daytime occurrence greater than 0.9, 50.12% are TEs occurring in various thrust faults in the Tianshan orogenic belt, and 12.31% are IEs or shallow tectonic earthquakes occurring mostly as clusters |
Diciembre de 2019 Just like weather forecasting, climate science relies heavily on simulating the Earth's weather patterns using complicated numerical models on very powerful super-computers. These models often represent 10s or 100s of thousands of lines of |
computer code and encompass as much understanding of how the real world operates as we can include into them. Their complexity means that it is very important to document what is in them and how they behave. In this commentary I explain why Roland Seferian and colleagues do a particularly good job of explaining and documenting the developments in their new model: “CNRM-ESM 1-1” |
Diciembre de 2019 The Petrology Workspace and Database (PWD; https://petro.wovodat.org) is a web-based data repository and interface that allows researchers to access, share, store, and manage petrological, mineralogical, and whole rock data in a contextualized manner. The uniqueness of the PWD is that it links images to different types of images and to compositional data providing a powerful visualization and framework of information at a wide range of scales, from the meter-sized outcrop to a few micrometers of a thin rock section. The PWD archives various data types and formats, and it includes multilevel data sets with an interactive |
online interface. The database is linked with other databases for volcanic eruptions (Smithsonian' Global Volcanism Program (GVP)) and for whole rock chemistry (EarthChem). The tool has four main features: (1) storage and management of spatial‐referenced data (e.g., from fieldwork notes to lab geochemical analysis); (2) a hierarchical relationship between different types of data using the Workspace interactive tool; (3) graph plots to visualize the data; and (4) the possibility of data sharing in a database structure that is managed by authorization levels. The PWD is a practical and efficient database management system that facilitates effective contextualized data preservation and sharing among scientists. It also can serve as a Data Management Plan and provide a framework for auditing research integrity both of which are becoming the new standards of most funding agencies and journals. |
Diciembre de 2019 Earthquakes are complex and diverse, ranging from energetic and destructive megathrust earthquakes to slow earthquakes. Complex earthquake rupture processes are generally modelled by prescribing a deterministic system and solving deterministic differential equations. However, such approaches cannot adequately capture the temporal evolution of a complex fault system because of the inherent |
unpredictability that results from various unprescribed processes. Such unpredictability may be better represented by time‐dependent stochastic fluctuations in addition to the deterministic estimates. Here, we demonstrate that the consideration of time‐dependent stochastic stress fluctuations in ordinary crack simulations can reproduce a variety of ruptures, including both crack‐like and pulse‐like ordinary (fast) earthquakes and slow earthquakes, by simply changing the strength drop and the initial stress level. The results indicate that stochasticity is effective for reproducing and better understanding the diversity of earthquakes, including slow earthquakes. |
Diciembre de 2019 Although plate tectonics has pushed the frontiers of geosciences in the past 50 years, it has legitimate limitations, and among them we focus on both the absence of dynamics in the theory and the difficulty of reconstructing tectonics when data are sparse. In this manuscript, we propose an anticipation experiment, proposing a singular outlook on plate tectonics in the digital era. We hypothesize that mantle convection models producing self‐consistently plate‐like behavior will capture the essence of the self‐organization of plate boundaries. Such models exist today in a preliminary fashion, and we use them here to build a database of mid‐ocean ridge and trench configurations. To extract knowledge from it, we |
develop a machine learning framework based on Generative Adversarial Networks (GANs) that learns the regularities of the self‐organization in order to fill gaps of observations when working on reconstructing a plate configuration. The user provides the distribution of known ridges and trenches, the location of the region where observations lack, and our digital architecture proposes a horizontal divergence map from which missing plate boundaries are extracted. Our framework is able to prolongate and interpolate plate boundaries within an unresolved region but fails to retrieve a plate boundary that would be completely contained inside of it. The attempt we make is certainly too early because geodynamic models need improvement and a larger amount of geodynamic model outputs, as independent as possible, is required. However, this work suggests applying such an approach to expand the capabilities of plate tectonics is within reach. |
Diciembre de 2019 Natural Hazards (NH), such as earthquakes, tsunamis, volcanic eruptions, and severe tropospheric weather events, generate acoustic and gravity waves that propagate upward and cause perturbations in the atmosphere and ionosphere. The first NH-related ionospheric disturbances were detected after the great 1964 Alaskan earthquake by ionosondes and Doppler sounders. Since then, many other observations confirmed the responsiveness of the ionosphere to natural hazards. Within the last two decades, outstanding progress has been made in this area owing to the development of networks of ground-based dual-frequency Global Navigation Satellite Systems |
(GNSS) receivers. The use of GNSS‐sounding has substantially enlarged our knowledge about the Solid Earth/ocean/atmosphere/ionosphere coupling and NH‐related ionospheric disturbances and their main features. Moreover, recent results have demonstrated that it is possible to localize NH from their ionospheric signatures, and also, if/when applicable, – to obtain the information about the NH source (i.e., the source location and extension, and the source onset time). Although all these results were obtained in retrospective studies, they have opened an exciting possibility for future ionosphere-based detection and monitoring of NH in near.real time. This article reviews the recent developments in the area of ionospheric detection of earthquakes, tsunamis and volcanic eruptions, and it discusses the future perspectives for this novel discipline. |
Diciembre de 2019 Convection of the liquid iron (Fe) outer core and electrical properties of Fe are responsible for the geodynamo that generates the geomagnetic field. Recent results showed the thermal conductivity of the core and related conductive heat flux may be much larger than previously accepted, suggesting that thermal convection would not be an energy |
source to power the geodynamo. Here we report experimental measurements of the electrical resistivity of solid and liquid Fe which show invariant values along the melting boundary at pressures up to 24 GPa. The observed resistivity invariance was extrapolated to Earth's predominantly Fe solid inner core and liquid outer core conditions and, using the Wiedemann-Franz law, the thermal conductivity was calculated. We calculate a conductive core heat flow of 8–9 TW at the core-mantle boundary. These results provide strong support for thermal convection as a geodynamo energy source |
Diciembre de 2019 The processes leading to the development of hail and the distribution of these events worldwide are reviewed. Microphysical and physical characteristics of hail development are described to provide context of the notable gaps in our understanding of what drives hail to grow large, or what determines how it falls to the ground. Distributional characteristics of hail are explored, utilizing both surface observations of hailstones and remotely sensed observational. datasets to identify opportunities and needs for new observations. These observational deficiencies contribute to our limited capacity to both forecast hail |
or its expected size, and reduce the effectiveness of using favorable conditions for hail development as a proxy to frequency where observations are unavailable. Given the substantive influences of both climate variability and the changing Earth system on hail, the latest understanding of their contributions to risk are addressed. Applying this understanding of the distribution and physical characteristics of hail, the damage by hail of agriculture and insured property are assessed. Much remains unknown about the processes leading to hail growth and environmental controls on hail occurrence, size and magnitude, particularly outside of the United States and Europe. A better understanding of the global occurrence of hail is also needed to better anticipate the hazard and associated impacts |
Diciembre de 2019 We use a basket geothermal heat exchanger during 518 hours to freeze a portion of soil. This field experiment is monitored using time lapse electrical conductivity tomography and a set of 47 in situ |
temperature sensors. A frozen soil core characterized by negative temperatures and low conductivity values (< 10-3 S m-1) develops over time. A petrophysical model describing the temperature dependence of the electrical conductivity in freezing conditions is applied to the field data and compared to two laboratory experiments performed with two core samples from the test site. The results show that this petrophysical model can be used to interpret field measurements bridging electrical conductivity to temperature and liquid water content. |
Noviembre de 2019 Deep low-frequency earthquakes (DLFEs) are ubiquitous seismic activities in the deep parts of volcanoes. Owing to the low signal-to-noise ratio, the seismic activities of DLFEs have not been characterized in detail; particularly, the linkage between DLFEs and shallow volcanic activity has |
not been understood sufficiently. In this study, numerous DLFEs have been successfully detected beneath the Hakone volcano, central Japan, by cross-correlating a template to the continuous seismic signals. The resulting seismic catalog reveals that DLFEs are activated prior to notable earthquake swarms in the shallow part of a volcano and to the crustal expansion caused by a pressure source at a depth of 7 km. Results indicate that the activation of DLFEs reflects the feeding of magmatic fluid from depth. The subsequent increment in the magmatic-fluid pressure triggers shallow volcanic activities. |
Noviembre de 2019 Tsunami resonance and coupled oscillation of shelf and bays modes has been reported to be important in tsunami wave amplification. The main objective of this work is to study the spatial pattern of natural oscillation modes and to analyze the influence of several resonators on the coast of the central Chile, which has a complex morphology with several bays, submarine canyons, and a wide continental shelf. First, natural oscillation modes were computed by means of modal analysis of local and regional domains. Second, a dense network of tide gauges |
and pressure sensors was analyzed to obtain background spectra inside bays. Third, tsunami spectra were computed from both tsunami records and numerical simulations. The results show that the use of modal analysis and background and tsunami spectra is effective for identifying natural oscillation modes. In addition, a dense network of tide gauges is useful to validate the spatial pattern of these natural modes. It was observed that larger resonators and the shelf are important in coupling oscillation with local bays, such that large amplification can be observed. Finally, this analysis allowed the diverse effects of 2010 and 2011 tsunamis in the bays of central Chile to be explained, making it possible to better address tsunami mitigation measures and the preparedness of coastal communities. |
Noviembre de 2019 A key goal of earthquake early warning (EEW) systems is to alert populations who may be affected by a particular level of ground shaking so that they can take action to reduce impacts of that shaking, such as injuries, damages to physical infrastructure, or emotional distress. Most EEW systems work by rapidly determining the location and size of an earthquake, estimating shaking levels, and then distributing an alert to potentially affected populations. But EEW systems are limited by how rapidly the size of an earthquake can be determined |
as well as the details of the earthquake rupture process, the path of the seismic waves, and the alert distribution mechanism. And we are just beginning to understand how people respond to earthquake alerts, often relying on anecdotes. Determining the appropriate shaking intensities for public warnings requires understanding the range of individual and societal responses to earthquake alerts. The decision on when to issue earthquake alerts must balance the technical capabilities and potential outcomes, both desired and undesired, when choosing a ground-motion alerting threshold. Only when benefits outweigh the risks and users are prepared for alerts should they be used to warn the public about the possibility of earthquake shaking. |
Noviembre de 2019 The Moon is known to have a small liquid core, and it is thought that in the distant past the core may have produced strong magnetic fields recorded in lunar samples. Here we implement a numerical model of lunar orbital and rotational dynamics that includes the effects of a liquid core. In agreement with previous work, we find that the lunar core is dynamically decoupled from the lunar mantle and that this decoupling happened very early in lunar history. Our model predicts that the lunar core rotates subsynchronously, and the difference between the core and the mantle rotational rates |
was significant when the Moon had a high forced obliquity during and after the Cassini State transition. We find that the presence of the lunar liquid core further destabilizes synchronous rotation of the mantle for a wide range of semimajor axes centered around the Cassini State transition. Core-mantle boundary torques make it even more likely that the Moon experienced large‐scale inclination damping during the Cassini State transition. We present estimates for the mutual core‐mantle obliquity as a function of Earth‐Moon distance, and we discuss plausible absolute time lines for this evolution. We conclude that our results are consistent with the hypothesis of a precession‐driven early lunar dynamo and may explain the variability of the inferred orientation of the past lunar dynamo. |
Noviembre de 2019 Postseismic deformation following large earthquakes has generally been analyzed via viscoelastic simulations or regression analyses that employ logarithmic and/or exponential functions. Here we introduce a machine learning approach, the recurrent neural network, to more accurately forecast postseismic deformation and constrain its characteristics. We use Global Navigation Satellite System time-series data (horizontal components) |
from northeastern Japan since the 2011 Tohoku-oki megathrust earthquake to assess the feasibility of this machine learning approach. We perform numerical experiment to examine the accuracy of the neural network forecast, compare the results with those from regression analyses, and confirm the improved accuracy of the neural network forecast. The spatiotemporal evolution of the differences between the observation data and forecast results implies alterations in the source of postseismic deformation, which may have occurred in 2013. We can extract detailed information on the spatiotemporal evolution of postseismic signals by implementing this new machine‐learning approach. |
Noviembre de 2019 On 5 February 2016 (UTC), an earthquake with moment magnitude 6.4 occurred in southern Taiwan, known as the 2016 (Southern) Taiwan earthquake and 2016 Meinong earthquake. In this study, evidences of seismic earthquake precursors |
for this earthquake event are investigated. Results show that ionospheric anomalies in total electron content (TEC) can be observed before the earthquake. These anomalies were obtained by processing TEC data, where such TEC data are calculated from phase delays of signals observed at densely arranged ground-based stations in Taiwan for Global Navigation Satellite Systems. This shows that such anomalies were detected within 1 hr before the event. |
Noviembre de 2019 Tension cracks were generated by past megathrust earthquakes along the coastal forearc of Chile-Peru. To explain why elastic rebound in an offshore earthquake can cause widespread permanent deformation onshore, we propose a model in which the near-surface material exhibits viscoelastic behavior, analogous to laboratory-observed |
behavior of petroleum reservoir rocks. Because of near-surface relaxation, interseismic deformation builds up stress only in the deeper crust. Elastic rebound of the deeper crust during an earthquake induces near-surface tension to generate cracks. We numerically demonstrate the proposed mechanism using hypothetical and real megathrust earthquakes. The location of the zone of peak tension, assumed to be responsible for the crack generation, is controlled by downdip rupture termination. A rupture farther downdip or terminating more gradually causes the zone of peak tension to be farther landward and broader. The tension cracks thus may contain important information on megathrust rupture dynamics. |
Noviembre de 2019 Paleomagnetic records from sediments, archeological artifacts, and lava flows provide the foundation for studying geomagnetic field changes over 0-100 ka. Late Quaternary time-varying spherical harmonic models for 0--100 ka produce a global view used to evaluate new data records, study the paleomagnetic secular variation on centennial to multi-millennial timescales, and investigate extreme regional or global events such as the Laschamp geomagnetic excursion. Recent modeling results (GGF100k and LSMOD.2) are compared to previous studies based on regional or global stacks and averages of relative geomagnetic paleointensity variations. Time-averaged field structure is similar on Holocene, 100 ky, and |
million-year timescales. Paleosecular variation activity varies greatly over 0-100 ka, with large changes in field strength and significant morphological changes that are especially evident when field strength is low. GGF100k exhibits a factor of 4 variation in geomagnetic axial-dipole moment, and higher resolution models suggest much larger changes are likely during global excursions. There is some suggestion of recurrent field states resembling the present day South Atlantic Anomaly, but these are not linked to initiation or evolution of excursions. Several properties used to characterize numerical dynamo simulations as ``Earth-like” are evaluated and, in future, improved models may yet reveal systematic changes linked to the onset of geomagnetic excursions. Modeling results are useful in applications ranging from ground truth and data assimilation in geodynamo simulations to providing geochronological constraints, and modeling the influence of geomagnetic variations on cosmogenic isotope production rates. |
Noviembre de 2019 Subduction zones, the massive faults found where plates of dense ocean crust dive beneath continents, are the source of the world's largest earthquakes and tsunamis. Although GPS stations on land have revolutionized studies of the faults' |
movement, GPS radio signals cannot penetrate through the ocean to the sea floor, leaving large gaps in the study and hazard assessment of subduction zones. Techniques to track this movement, using GPS on ships tied to acoustic beacons on the sea floor, remain prohibitively expensive, though they have been embraced, with great success, in recent years by Japan. Now, U.S. scientists have developed a way to use ocean-going drones to replace ships, a move that many hope will greatly expand study of these faults. |
Noviembre de 2019 Tension cracks were generated by past megathrust earthquakes along the coastal forearc of Chile-Peru. To explain why elastic rebound in an offshore earthquake can cause widespread permanent deformation onshore, we propose a model in which the near-surface material exhibits viscoelastic behavior, analogous to laboratory-observed behavior of petroleum reservoir rocks. Because of |
near-surface relaxation, interseismic deformation builds up stress only in the deeper crust. Elastic rebound of the deeper crust during an earthquake induces near-surface tension to generate cracks. We numerically demonstrate the proposed mechanism using hypothetical and real megathrust earthquakes. The location of the zone of peak tension, assumed to be responsible for the crack generation, is controlled by downdip rupture termination. A rupture farther downdip or terminating more gradually causes the zone of peak tension to be farther landward and broader. The tension cracks thus may contain important information on megathrust rupture dynamics. |
Noviembre de 2019 In 2016, JGR: Planets became the first AGU journal to begin accepting plain language summaries as a component of research and review articles. Authors began widely participating in this new approach to sharing planetary science in clear language with growth from 18% to 52% of published articles having a summary from the first to last quarters of |
2017. In 2018, JGR: Planets joined several other AGU journals in making a plain language summary an expectation of all papers. Plain language summaries are an opportunity to make the rationale for, relevance of, and results from our work clear to a broad audience including students, science journalists, funders, and colleagues outside our specialty, among others. As adoption of and familiarity with, plain language summaries expands the impact of our work within our community and our society will grow too. |
Noviembre de 2019 Automated systems for detecting deformation in satellite interferometric synthetic aperture radar (InSAR) imagery could be used to develop a global monitoring system for volcanic and urban environments. Here, we explore the limits of a convolutional neural networks for detecting slow, sustained deformations in wrapped interferograms.Using synthetic data, we estimate a detection threshold of 3.9 cm for |
deformation signals alone and 6.3 cm when atmospheric artifacts are considered. Overwrapping reduces this to 1.8 and 5.2 cm, respectively, as more fringes are generated without altering signal to noise ratio. We test the approach on time series of cumulative deformation from Campi Flegrei and Dallol, where overwrapping improves classification performance by up to 15%. We propose a mean-filtering method for combining results of different wrap parameters to flag deformation. At Campi Flegrei, deformation of 8.5 cm/year was detected after 60 days and at Dallol, deformation of 3.5 cm/year was detected after 310 days. This corresponds to cumulative displacements of 3 and 4 cm consistent with estimates based on synthetic data. |
Noviembre de 2019 Viscosity and elasticity are material properties essential for understanding the composition, dynamics, and evolution of the Earth's core, yet their intrinsic connection as embedded in the general theory of viscoelasticity is not well explored. Here we use molecular dynamics to determine the viscoelasticity of liquid iron at conditions of the Earth's outer core. The frequency-dependent viscosity and shear modulus are determined from the power spectrum of the stress autocorrelation function (SACF). We find that the SACF is well characterized by a generalized Maxwell model containing two relaxation modes. The mode with |
shorter relaxation time (t1) corresponds to the motion of individual atoms, the other with longer relaxation time (t2) is associated with collective motions. As T decreases, the slow-decaying mode becomes more prominent with increasingly larger t2. In contrast, t1 remains nearly constant (~ 0.016 ps). The infinite frequency shear modulus (G8), which characterizes the instantaneous shear response, is found to be larger than the static shear modulus of hexagonal close-packed (hcp) iron of the same density and increases linearly with T. Based on these findings as well as seismic analyses (Tsuboi & Saito, 2002; Krasnoshchekov et al., 2005), the zero frequency viscosity (?0) of the lowermost outer core is inferred as 109 Pa·s. The likely material states exhibiting such viscosities are discussed. Moreover, we show that to retain the rigidity consistent with seismic observations, the ?0 of the inner core should be at least 1013 Pa·s. |
Noviembre de 2019 Although plate tectonics has pushed the frontiers of geosciences in the past 50 years, it has legitimate limitations and among them we focus on both the absence of dynamics in the theory, and the difficulty of reconstructing tectonics when data is sparse. In this manuscript, we propose an anticipation experiment, proposing a singular outlook on plate tectonics in the digital era. We hypothesize that mantle convection models producing self-consistently plate-like behavior will capture the essence of the self-organisation of plate boundaries. Such models exist today in a preliminary fashion and we use them here to build a database of mid-ocean ridge and trench configurations. To extract knowledge from it we |
develop a machine learning framework based on Generative Adversarial Networks (GANs) that learns the regularities of the self-organisation in order to fill gaps of observations when working on reconstructing a plate configuration. The user provides the distribution of known ridges and trenches, the location of the region where observations lack, and our digital architecture proposes a horizontal divergence map from which missing plate boundaries are extracted. Our framework is able to prolongate and interpolate plate boundaries within an unresolved region, but fails to retrieve a plate boundary that would be completely contained inside of it. The attempt we make is certainly too early because geodynamic models need improvement and a larger amount of geodynamic model outputs, as independent as possible, is required. However, this work suggests applying such an approach to expand the capabilities of plate tectonics is within reach. |
Noviembre de 2019 The Generic Mapping Tools (GMT) software is ubiquitous in the Earth and ocean sciences. As a cross-platform tool producing high-quality maps and figures, it is used by tens of thousands of scientists around the world. The basic syntax of GMT scripts has evolved very slowly since the 1990s, despite the fact that GMT is generally perceived to have a steep learning curve with many pitfalls for beginners and . |
experienced users alike. Reducing these pitfalls means changing the interface, which would break compatibility with thousands of existing scripts. With the latest GMT version 6, we solve this conundrum by introducing a new “modern mode” to complement the interface used in previous versions, which GMT 6 now calls “classic mode.” GMT 6 defaults to classic mode and thus is a recommended upgrade for all GMT 5 users. Nonetheless, new users should take advantage of modern mode to make shorter scripts, quickly access commonly used global data sets, and take full advantage of the new tools to draw subplots, place insets, and create animations |
Octubre de 2019 We study the structure and tectonics of the collision zone between the Nazca Ridge (NR) and the Peruvian margin constrained by seismic, gravimetric, bathymetric, and natural seismological data. The NR was formed in an on-ridge setting, and it is characterized by a smooth and broad shallow seafloor (swell) with an estimated buoyancy flux of ~7 Mg/s. The seismic results show that the NR hosts an oceanic lower crust 10–14 km thick with velocities of 7.2–7.5 km/s suggesting intrusion of magmatic material from the hot spot plume to the oceanic plate. Our results show evidence for |
subduction erosion in the frontal part of the margin likely enhanced by the collision of the NR. The ridge-trench collision zone correlates with the presence of a prominent normal scarp, a narrow continental slope, and (uplifted) shelf. In contrast, adjacent of the collision zone, the slope does not present a topographic scarp and the continental slope and shelf become wider and deeper. Geophysical and geodetic evidence indicate that the collision zone is characterized by low seismic coupling at the plate interface. This is consistent with vigorous subduction erosion enhanced by the subducting NR causing abrasion and increase of fluid pore pressure at the interplate contact. Furthermore, the NR has behaved as a barrier for rupture propagation of megathrust earthquakes (e.g., 1746 Mw 8.6 and 1942 Mw 8.1 events). In contrast, for moderate earthquakes (e.g., 1996 Mw 7.7 and 2011 Mw 6.9 events), the NR has behaved as a seismic asperity nucleating at depths >20 km. |
Octubre de 2019 Tsunamis are one of the most destructive effects of subduction zone earthquakes. Directly observing and understanding the generation and propagation of tsunamis remain challenging due to limited offshore instrumentation and a sparse catalog of large events. This makes linking characteristics of the earthquake rupture to their effect on tsunami generation difficult. While past studies explored how varying earthquake source geometries affect tsunami nucleation, little has been done to examine the role of the kinematic component of rupture on the tsunami; we explore these effects in this study. While past studies have examined the kinematic |
effect using coastal tide gauge data, we expand this examination to more recent pressure gauges. We identify a consistent rotation of the main beam of tsunami energy when using a kinematic model, affecting far‐field hazards. We also identify a delay in tsunami arrival times at both coastal and open ocean gauges that can be as long as the total source duration. For large earthquakes, this delay introduces non‐negligible mapping errors when employing open ocean tsunami data for source characterizations. As a result of our findings, we recommend including a kinematic component to tsunami modeling when studying events with source durations over 120 s and using recordings from open ocean pressure gauges. We also find that when focusing purely on coastal gauge data and near‐source hazards, the kinematic component is a much smaller contribution to the source uncertainty and can be ignored. |
Octubre de 2019 Dynamic earthquake triggering can be used to investigate the responses of faults to stress disturbances. We develop a new method to detect dynamic triggering by estimating high-frequency energy change before and during teleseismic waves using the HIgh-Frequency power Integral ratio (HiFi). Our method is able to identify local events |
independent of earthquake catalog or subjective judgements. The significance in energy change is evaluated by a statistical analysis of the background ratio in a large number of days, which can suppress the influence of noise and variations in the background seismicity, and yield a confidence level of dynamic triggering (0–1). We apply the HiFi method to the Geysers Geothermal Field in California and the results are largely consistent with previous reports from the β-statistic. By comparing the results of HiFi and β-statistic, we select a confidence level range of 0.918–0.947 as the optimum threshold to identify dynamic triggering in the region. |
Octubre de 2019 We analyze two high-quality Southern Californian earthquake catalogues, one with focal mechanisms, to statistically model and test for dependencies of the earthquake-size distribution, the b values, on both faulting style and depth. In our null hypothesis, b is assumed constant. We then develop and calibrate one model based only on faulting style, |
another based only on depth dependence and two models that assume a simultaneous dependence on both parameters. We develop a new maximum-likelihood estimator corrected for the degrees of freedom to assess models' performances. Our results show that all models significantly reject the null hypothesis. The best performing is the one that simultaneously takes account of depth and faulting style. Our results suggest that differential stress variations in the Earth's crust systematically influence b values and that this variability should be considered for contemporary seismic hazard studies. |
Octubre de 2019 The extension of the neutral sodium (Na) layer into the thermosphere (up to 170 km) has recently been observed at low and high latitudes using a Na lidar. However, the geophysical mechanisms and implications of its formation are currently unknown. In this study, we conduct an advanced 2D numerical simulation of the Na and Na+ variations in the E and F regions at low latitudes. The numerical simulations are used to investigate the contributions |
of the electromagnetic force, neutral wind, diffusion, and gravity. The simulations lead to three major findings. First, Na+ in the subtropical region of the geomagnetic equator acts as the major reservoir of the neutral sodium, and its distribution during nighttime is mostly below 200 km due to the combined effect of the vertical component of the ExB drift and Coulomb-induced drift. Second, we find that the fountain effect has little influence on the behavior of Na in the nighttime. Third, the probable explanation for the frequent generation of the thermospheric sodium layer during spring equinox at Cerro Pachón, Chile is attributed to the large vertical neutral transport generated by large vertical wind perturbations of unknown origin, with a magnitude exceeding 10 m/s that is closely associated with the semi-diurnal tide. |
Octubre de 2019 On Feb. 5 2016 (UTC), an earthquake with moment magnitude 6.4 occurred in southern Taiwan, known as the 2016 (Southern) Taiwan earthquake and 2016 Meinong earthquake. In this study, evidences of seismic earthquake precursors for this |
earthquake event are investigated. Results show that ionospheric anomalies in Total Electric Content (TEC) can be observed before the earthquake. These anomalies were obtained by processing TEC data, where such TEC data are calculated from phase delays of signals observed at densely arranged ground-based stations in Taiwan for Global Navigation Satellite Systems. This shows that such anomalies were detected within 1 hour before the event. |
Octubre de 2019 Tension cracks were generated by past megathrust earthquakes along the coastal forearc of Chile-Peru. To explain why elastic rebound in an offshore earthquake can cause widespread permanent deformation onshore, we propose a model in which the near-surface material exhibits viscoelastic behavior, analogous to laboratory-observed |
behavior of petroleum reservoir rocks. Because of near-surface relaxation, interseismic deformation builds up stress only in the deeper crust. Elastic rebound of the deeper crust during an earthquake induces near-surface tension to generate cracks. We numerically demonstrate the proposed mechanism using hypothetical and real megathrust earthquakes. The location of the zone of peak tension, assumed to be responsible for the crack generation, is controlled by downdip rupture termination. A rupture farther downdip or terminating more gradually causes the zone of peak tension to be farther landward and broader. The tension cracks thus may contain important information on megathrust rupture dynamics. |
Octubre de 2019 The Generic Mapping Tools (GMT) software is ubiquitous in the Earth and Ocean sciences. As a cross-platform tool producing high quality maps and figures, it is used by tens of thousands of scientists around the world. The basic syntax of GMT scripts has evolved very slowly since the 1990s, despite the fact that GMT is generally perceived to have a steep learning curve with many pitfalls for |
beginners and experienced users alike. Reducing these pitfalls means changing the interface, which would break compatibility with thousands of existing scripts. With the latest GMT version 6, we solve this conundrum by introducing a new “modern mode” to complement the interface used in previous versions, which GMT 6 now calls “classic mode”. GMT 6 defaults to classic mode and thus is a recommended upgrade for all GMT 5 users. Nonetheless, new users should take advantage of modern mode to make shorter scripts, quickly access commonly used global data sets, and take full advantage of the new tools to draw subplots, place insets, and create animations. |
Octubre de 2019 Seismic signals from ocean‐solid Earth interactions are ubiquitously recorded on our planet. However, these wavefields are typically incoherent in the time domain limiting their utilization for understanding ocean dynamics or solid Earth properties. In contrast, we find that during large storms such as hurricanes and Nor'easters the interaction of long-period ocean waves with shallow seafloor features located near the edge of |
continental shelves, known as ocean banks, excites coherent transcontinental Rayleigh wave packets in the 20 to 50 s period band. These “stormquakes” migrate coincident with the storms, but are effectively spatiotemporally focused seismic point sources with equivalent earthquake magnitudes that can be greater than 3.5. Stormquakes thus provide new coherent sources to investigate Earth structure in locations that typically lack both seismic instrumentation and earthquakes. Moreover, they provide a new geophysical observable with high spatial and temporal resolution with which to investigate ocean wave dynamics during large storms. |
Octubre de 2019 There is a growing list of examples for the existence of the signal-to-noise paradox, where in the ensemble-based climate prediction, the model ensemble mean forecast generally shows higher correlations with observations than with individual ensemble members. This seems to lead to a paradox that the model makes better predictions for the real world than predicting itself. Here we |
introduce a Markov model to represent the ensemble forecasts and reproduce the signal-to-noise paradox, which we argue is primarily dependent on the magnitude of the persistence and noise variance between the models and the corresponding observations. The monthly North Atlantic Oscillation indices based on uninitialized historical simulations of 40 CMIP5 models have been analyzed, suggesting that the signal‐to‐noise paradox is common in currently available coupled models, and the paradox is not due to problems with initialization processes used in the seasonal-to-decadal predictions in previous studies and is instead a general model problem. |
Septiembre de 2019 The current goals of the astrobiology community are focused on developing a framework for the detection of biosignatures, or evidence thereof, on objects inside and outside of our solar system. A fundamental aspect of understanding the limits of habitable environments (surface liquid water) and detectable signatures thereof is the study of where the boundaries of such environments can occur. Such studies provide the basis for understanding how a once inhabitable planet might come to be uninhabitable. The archetype of such a planet is arguably Earth's sibling planet, Venus. Given the need to define the conditions that can rule out bio- |
related signatures of exoplanets, Venus provides a unique opportunity to explore the processes that led to a completely uninhabitable environment by our current definition of the term. Here we review the current state of knowledge regarding Venus, particularly in the context of remote-sensing techniques that are being or will be employed in the search for and characterization of exoplanets. We discuss candidate Venus analogs identified by the Kepler and TESS exoplanet missions and provide an update to exoplanet demographics that can be placed in the potential runaway greenhouse regime where Venus analogs are thought to reside. We list several major outstanding questions regarding the Venus environment and the relevance of those questions to understanding the atmospheres and interior structure of exoplanets. Finally, we outline the path toward a deeper analysis of our sibling planet and the synergy to exoplanetary science. |
Septiembre de 2019 Information on structure, stress, and their interrelationship is essential for understanding structurally controlled geothermal permeability. Active fault mapping, borehole image analysis, and well testing in the Te Mihi geothermal area, New Zealand, allows us to refine structural and fluid flow architecture of this resource. The Te Mihi area is structurally complex, comprising a set of NW dipping master faults containing pervasive SE dipping antithetic and splay structures in their hanging walls. These faults are also intersected by E-W striking faults. A localized, N‐S striking structural trend is also observed at Te Mihi. In consideration with Global Navigation Satellite System velocity vectors, both active NE-SW and E‐W striking faults create |
biaxial extension at Te Mihi, though the observed NE-SW SHmax direction suggests that contemporary extension is NW‐SE dominated. Stress field perturbations coincide with structural complexities like fault splays and intersections and/or proximity to recently active E-W and NE‐SW striking structures. Borehole fluid flow at Te Mihi is concentrated at NW dipping master fault intersections, travel time fractures on acoustic image logs, halo fractures on resistivity image logs, NE‐SW and E‐W striking fractures, intervals of high fracture density, and spatial concentrations of wide aperture fractures and recently active NE-SW and E‐W striking fractures. This study suggests Te Mihi geothermal expression results from biaxial extension evident from active structural trend intersections and the predominance of NE-SW and E‐W striking structures within permeable well zones. Biaxial extension is therefore an important control on crustal fluid flow within the Taupo Volcanic Zone and thus geothermal resource delineation. |
Septiembre de 2019 While power law distributions in seismic moment and interevent times are ubiquitous in regional earthquake catalogs, the statistics of individual faults remains controversial. Continuum fault models without heterogeneity typically produce characteristic earthquakes or a narrow range of sizes, leading to the view that regional statistics originate from interaction of multiple faults. I present theoretical arguments and numerical simulations |
demonstrating that seismicity on homogeneous planar faults can span several orders of magnitude in rupture dimensions and interevent times, if the fault dimension W is sufficiently large compared to a characteristic length Lcrit, related to the nucleation dimension. Large faults are increasingly less characteristic, with the fraction of system-size ruptures proportional to (Lcrit/W)1/2. Earthquake statistics for large W/Lcrit is remarkably close to nature, exhibiting Omori decay and power law distributed rupture lengths. Simple crack models are consistent with a Gutenberg-Richter distribution with b=3/4 and provide a physical basis for these distributions on individual faults. |
Septiembre de 2019 When planets receive insolation above a certain critical value called the runaway threshold, liquid surface water vaporizes completely, which forms the inner edge of the habitable zone. Because land planets can emit a large amount of radiation from the dry tropics, they have a higher runaway threshold than aqua planets do. Here we systematically investigated the runaway threshold for various surface water distributions using a three-dimensional dynamic atmosphere model. The runaway threshold for the meridionally uniform surface water distribution increases from the typical value for the aqua planet regime (~130% S0) to one |
for the land planet regime (~155% S0) as the dry surface area increases, where S0 is the present Earth's insolation. Although this result is similar to the previous work considering zonally uniform surface water distributions, the runaway threshold for the land planet regime is quite low compared to that of the previous work. This is because a part of the tropical atmosphere is always wet for the meridionally uniform case. We also considered the surface water distributions determined by the Earth's, Mars's, and Venus's topographies. We found that their runaway thresholds are close to that for the meridionally uniform cases, and the amount of water at the boundary between an aqua planet regime and land planet regime is around 10% of the Earth's ocean. This clearly shows that the runaway threshold is not determined uniquely by the luminosity of the central star, but it has a wide range caused by the surface water distribution of the terrestrial water planet itself. |
Septiembre de 2019 Taking the full complexity of subduction zones into account is important for realistic modelling and hazard assessment of subduction zone seismicity and associated tsunamis. Studying seismicity requires numerical methods that span a large range of spatial and temporal scales. We present the first coupled framework that resolves subduction dynamics over millions of years and earthquake dynamics down to fractions of a second. Using a two‐dimensional geodynamic seismic cycle (SC) method, we model 4 million years of subduction followed by cycles of spontaneous megathrust events. At the initiation of one such SC event, we |
geometry, fault stress and strength, and heterogeneous material properties to a dynamic rupture (DR) model. Coupling leads to spontaneous dynamic rupture nucleation, propagation and arrest with the same spatial characteristics as in the SC model. It also results in a similar material‐dependent stress drop, although dynamic slip is significantly larger. The DR event shows a high degree of complexity, featuring various rupture styles and speeds, precursory phases, and fault reactivation. Compared to a coupled model with homogeneous material properties, accounting for realistic lithological contrasts doubles the amount of maximum slip, introduces local pulse‐like rupture episodes, and relocates the peak slip from near the downdip limit of the seismogenic zone to the updip limit. When an SC splay fault is included in the DR model, the rupture prefers the splay over the shallow megathrust, although wave reflections do activate the megathrust afterwards. |
Agosto de 2019 Hydrologic responses to earthquakes such as streamflow increases, water-level changes, and changes in geyser eruption frequency often reflect changes in permeability caused by seismic waves. |
The dynamic nature of permeability, as revealed by coseismic hydrologic phenomena, holds implications for groundwater systems, geothermal resources, mineral resources, and geologic hazards. Analysis of water-level responses to solid Earth tides and changes in atmospheric pressure provides a passive way to continuously monitor changes in permeability and storage properties in tectonically active regions. |
Agosto de 2019 We investigate earthquake‐induced landslides using a geostatistical model featuring a latent spatial effect (LSE). The LSE represents the spatially structured residuals in the data, which remain after adjusting for covariate effects. To determine whether the LSE captures the residual signal from a given trigger, we test the LSE in reproducing the pattern of seismic shaking from the distribution of seismically induced landslides, without prior knowledge of the earthquake being included in the model. We assessed the landslide intensity, that is, the expected number of landslides per mapping unit, for the area in which landslides triggered by the Wenchuan and Lushan |
earthquakes overlap. We examined this area to test our method on landslide inventories located in near and far fields of the earthquake. We generated three models for both earthquakes: (i) seismic parameters only (proxy for the trigger); (ii) the LSE only; and (iii) both seismic parameters and the LSE. The three configurations share the same morphometric covariates. This allowed us to study the LSE pattern and assess whether it approximated the seismic effects. Our results show that the LSE reproduced the shaking patterns for both earthquakes. In addition, the models including the LSE perform better than conventional models featuring seismic parameters only. Due to computational limitations we carried out a detailed analysis for a relatively small area (2,112 km2), using a data set with higher spatial resolution. Results were consistent with those of a subsequent analysis for a larger area (14,648 km2) using coarser-resolution data. |
Agosto de 2019 In a metal, as in Earth's core, the thermal and electrical conductivities are assumed to be correlated. In a planetary dynamo this implies a contradiction: that both electrical conductivity, which makes it easier to induce current and magnetic field, and conductive heat transport, which hinders thermal convection, should increase simultaneously. Here we show that this |
contradiction implies that the magnetic induction rate peaks at a particular value of electrical and thermal conductivity and derive the low and high conductivity limits for thermal dynamo action. A dynamo regime diagram is derived as a function of electrical conductivity and temperature for Earth's core that identifies four distinct dynamo regimes: no dynamo, thermal dynamo, compositional dynamo, and thermocompositional dynamo. Estimates for the temperature dependent electrical conductivity of the core imply that the geodynamo may have come close to its high-conductivity “no dynamo” limit prior to inner core nucleation, consistent with recent paleomagnetic observations. |
Agosto de 2019 Concept of fractals and power‐law in statistical and geometrical datasets is rather matured. However, the application part of the fractal theory is not yet commensurate with the theoretical literature available. In this invited review, we take a dig at the range of data sets to demonstrate their fractal/scaling behavior for instance well logs and |
geological features such as fractures, which exhibit scaling behavior. The range of topics discussed in this paper are based on the concept that physical and geometrical property of the earth follows scaling behavior. Based on the observations and available research we aim to address the question ‘Is geology scaling?’. Further, we elaborate on one of the applications of fractal concepts in designing an operator for the colored inversion of seismic data, which is very efficient, and does not need a background model to do the seismic inversion in contrast to classical seismic inversion methods. |
Agosto de 2019 Society's progress along the four corners of prepare, absorb, respond and adapt resilience square is uneven, in spite of our understanding of the foundational science and a growing sense that urgent action is needed. The resilience vignettes |
describe the meaning and impact of current and near term change in four major domains: human health impacts from air pollution, coastal inundation from sea‐level rise, damaging earthquakes in populated areas, and impacts from extreme precipitation. Given our understanding of the scientific principles, societal action, from preparation to adaption, will be critical in minimizing the negative impacts of change. The unprecedented rates of change in today's Earth system argue for urgent action in support of a resilient global society. |
Agosto de 2019 A major goal in Earth Science has been to understand how geochemical characteristics of lavas at the Earth's surface relate to the location and formation history of specific regions in the Earth's interior. For example, some of the strongest evidence for the preservation of primitive material comes from low 4He/3He ratios in ocean island basalts, but the location of the primitive helium reservoir(s) remains unknown. Here we combine whole-mantle seismic tomography, simulations of mantle flow, and a global compilation of new and existing measurements of the 4He/3He ratios in ocean island basalts to constrain the source location of primitive 4He/3He material. Our geodynamic simulations predict the present-day |
surface expression of plumes to be laterally offsetfrom their lower mantle source locations. When this lateral offset is accounted for, a strong relationship emerges between minimum 4He/3He ratios in oceanic basalts and seismically slow regions, which are generally located within the two large, low shear-wave velocity provinces (LLSVPs). Conversely, no significant relationship is observed between maximum 208Pb*/206Pb* ratios and seismically slow regions in the lowermost mantle. These results indicate that primitive materials are geographically restricted to LLSVPs, while recycled materials are more broadly distributed across the lower mantle. The primitive nature of the LLSVPs indicates these regions are not composed entirely of recycled slabs, while complementary xenon and tungsten isotopic anomalies require the primitive portion of the LLSVPs to have formed during Earth's accretion, survived the Moon-forming giant impact and remained relatively unmixed during the subsequent 4.5 billion years of mantle convection. |
Agosto de 2019 We analyzed a catalog of 31 published earthquake chronologies to assess the commonality of quasiperiodic earthquake recurrence across a range of fault types and tectonic settings. The statistical approach we employ differs from previous methods in that it explicitly incorporates numeric uncertainties in the earthquake chronologies while |
recognizing that random sequences of events (against which the chronologies are tested) may appear to be less disordered over the short time scales typical of most published records. Our results show that 58% of the chronologies support an interpretation of quasiperiodic recurrence (probability of random recurrence < 10%). These include strike-slip, normal, and reverse faults in both plate-boundary and intraplate environments, which exhibit evidence for quasiperiodic recurrence with comparable frequency. We conclude that quasiperiodic failure is likely the norm for faults in the seismogenic crust and that stress renewal is a first-order control on fault rupture across a wide range of tectonic settings. |
Agosto de 2019 In 2013 and 2018, earthquake swarms with a maximum moment magnitude of 4.5 occurred ~5 km from the northern section of the Dead Sea Transform Fault. Here we show that aquifer pressure data, interferometric synthetic aperture radar surface deformation time series, and seismic monitoring suggest that groundwater withdrawal triggered these earthquakes. Continuous groundwater extraction from several wells located |
~10 km west of the swarms has accelerated since 2010 and resulted in a total decrease of ~50 m of the groundwater level at the time of the 2018 earthquake swarm. The withdrawal also corresponds to surface subsidence of ~10 mm/year based on repeat interferometric synthetic aperture radar measurements. The temporal correlation, extensive subsidence, anomalous swarm characteristics, and normal faulting orientation suggest a connection between the groundwater withdrawal and recent earthquakes. Poroelastic modeling demonstrates that pumping-induced pore pressure decrease west of the earthquake could have caused significant dilatational stresses that led to normal faulting events outside the aquifer. |
Agosto de 2019 Hydrologic responses to earthquakes such as streamflow increases, water-level changes, and changes in geyser eruption frequency often reflect changes in permeability caused by seismic waves. |
The dynamic nature of permeability, as revealed by coseismic hydrologic phenomena, holds implications for groundwater systems, geothermal resources, mineral resources, and geologic hazards. Analysis of water-level responses to solid Earth tides and changes in atmospheric pressure provides a passive way to continuously monitor changes in permeability and storage properties in tectonically active regions. |
Agosto de 2019 Saturated hydraulic conductivity (Ks) is a fundamental soil property that regulates the fate of water in soils. Its measurement, however, is cumbersome and instead pedotransfer functions (PTFs) are routinely used to estimate it. Despite much progress over the years, the performance of current generic PTFs estimating Ks remains poor. Using machine learning, high-performance computing, and a large database of over 18,000 soils, we developed new PTFs to predict Ks. We compared the performances of four machine learning algorithms and different predictor sets. We evaluated the relative importance of soil properties |
in explaining Ks. PTF models based on boosted regression tree algorithm produced the best models with root-mean-squared log-transformed error in ranges of 0.4 to 0.3 (log10(cm/day)). The 10th percentile particle diameter (d10) was found to be the most important predictor followed by clay content, bulk density (?b), and organic carbon content (C). The sensitivity of Ks to soil structure was investigated using ?b and C as proxies for soil structure. An inverse relationship was observed between ?b and Ks, with the highest sensitivity at around 1.8 g/cm3 for most textural classes. Soil C showed a complex relationship with Ks with an overall positive relation for fine-textured and midtextured soils but an inverse relation for coarse-textured soils. This study sought to maximize the extraction of information from a large database to develop generic machine learning-based PTFs for estimating Ks. Models developed here have been made publicly available and can be readily used to predict Ks. |
Agosto de 2019 Large earthquakes initiate chains of surface processes that last much longer than the brief moments of strong shaking. Most moderate- and large-magnitude earthquakes trigger landslides, ranging from small failures in the soil cover to massive, devastating rock avalanches. Some landslides dam rivers and impound lakes, which can collapse days to centuries later, and flood mountain valleys for hundreds of kilometers downstream. Landslide deposits on slopes can remobilize during heavy rainfall and evolve into debris flows. Cracks and fractures can form and widen on mountain crests and flanks, promoting increased frequency of landslides that lasts for |
decades. More gradual impacts involve the flushing of excess debris downstream by rivers, which can generate bank erosion and floodplain accretion as well as channel avulsions that affect flooding frequency, settlements, ecosystems, and infrastructure. Ultimately, earthquake sequences and their geomorphic consequences alter mountain landscapes over both human and geologic time scales. Two recent events have attracted intense research into earthquake-induced landslides and their consequences: the magnitude M 7.6 Chi-Chi, Taiwan earthquake of 1999, and the M 7.9 Wenchuan, China earthquake of 2008. Using data and insights from these and several other earthquakes, we analyze how such events initiate processes that change mountain landscapes, highlight research gaps, and suggest pathways toward a more complete understanding of the seismic effects on the Earth's surface. |
Agosto de 2019 The simulation speed of two-dimensional hydrodynamic flood models is a limiting factor when catchments are large, a considerable number of simulations is required (e.g., exploratory modeling, Monte‐Carlo flood simulations, or predicting probabilistic flood maps), or when there is a need for real-time flood emergency management. Rapid Flood Models (RFMs) that rely only on topographic depressions and the water balance equation have been successfully implemented to predict maximum urban flood inundation depths within seconds to a few minutes. However, the preprocessing step (identification of depressions and their attributes) and the postprocessing step (marking up possible flow paths of flood water in between flooded depressions) of RFMs is time consuming. In this study, we developed a new fast flood inundation model based on the cellular automata (CA) approach. The new model does not require the |
preprocessing and postprocessing steps of RFMs and therefore can provide more simulation speed. The performance of our new model, referred to as Cellular Automata fast flood evaluation (CA-ffé), was compared to two well‐known hydrodynamic flood models (HEC-RAS and TUFLOW) in 20 simulation experiments conducted in five different urban subcatchments. CA-ffé predicted maximum inundation depth with reasonable accuracy in a matter of seconds to a few minutes for a single rainfall event simulation. The CA-ffé model performed exceptionally well in areas with low‐lying depressions. However, in areas where floodwaters had higher momentum and velocity, the model usually was not able to estimate inundation depths calculated by HEC-RAS or TUFLOW. CA-ffé's key drawback is also its inability to represent the temporal evolution of flooding and flow velocities. Nevertheless, its ability to provide spatial flood extents and depths in a fraction of the time compared to its hydrodynamic counterparts is a significant advancement toward exploratory approaches for water systems planning, model-based predictive control, and real‐time flood management. |
Agosto de 2019 A modification of a previously introduced electrically small antenna is presented with tuning methods for continuous band coverage for ionospheric heating (~3–10 MHz). Consisting of a small loop antenna inductively coupled to a capacitively loaded loop (CLL), the design may be tuned ±50% of the center of the band by simply adjusting the capacitance of |
the CLL. Abandoning the use of lossy materials for tuning such as solid dielectrics or ferrites, the antenna is greater than 80% efficient across its tuning range. A tenth scale prototype with electromechanical geometry tuning is tested for frequency range and tuning capability especially at the low-frequency end where port reflection losses tend to dominate. Tuning of the small loop antenna‐CLL coupling is used to mitigate this matching issue, which was demonstrated on the physical antenna model. Experimentally, a tuning range of 33.5–117.5 MHz is achieved with low reflection achievable across the range. |
Agosto de 2019 It is of paramount importance to independently assess the spatiotemporal uniqueness of a proposed regional precursor initiated a few months before the 2011 Mw 9.0 Tohoku‐Oki earthquake. The precursor has been inferred from GRACE-derived gravitational gradient changes and has been interpreted as a large‐scale aseismic . |
movement of the subducting plate along the Japan Trench. We design a hypothesis test, which enables the rigorous assessment of the statistical significance of short-term gradient anomalies at any time in any place and the quantitative comparison of the resolved anomalies with the proposed precursory signal. We find that the proposed precursory changes are not statistically unique either in time or in space. Therefore, the precursor cannot be attributed to the proposed dynamic acceleration of the subduction process. Instead, such transient features more likely represent temporally correlated GRACE observation errors or signals associated with other processes |
Agosto de 2019 Saturated hydraulic conductivity (Ks) is a fundamental soil property that regulates the fate of water in soils. Its measurement, however, is cumbersome and instead pedotransfer functions (PTFs) are routinely used to estimate it. Despite much progress over the years, the performance of current generic PTFs estimating Ks remains poor. Using machine learning, high‐performance computing, and a large database of over 18,000 soils, we developed new PTFs to predict Ks. We compared the performances of four machine learning algorithms and different predictor sets. We evaluated the relative importance of soil properties |
in explaining Ks. PTF models based on boosted regression tree algorithm produced the best models with root-mean-squared log-transformed error in ranges of 0.4 to 0.3 (log10(cm/day)). The 10th percentile particle diameter (d10) was found to be the most important predictor followed by clay content, bulk density (ρb), and organic carbon content (C). The sensitivity of Ks to soil structure was investigated using ρb and C as proxies for soil structure. An inverse relationship was observed between ρb and Ks, with the highest sensitivity at around 1.8 g/cm3 for most textural classes. Soil C showed a complex relationship with Ks with an overall positive relation for fine‐textured and midtextured soils but an inverse relation for coarse‐textured soils. This study sought to maximize the extraction of information from a large database to develop generic machine learning-based PTFs for estimating Ks. Models developed here have been made publicly available and can be readily used to predict Ks. |
Agosto de 2019 Earthquake source time functions carry information about the complexity of seismic rupture. We explore databases of earthquake source time functions and find that they are composed of distinct peaks that we call subevents. We observe that earthquake |
complexity, as represented by the number of subevents, grows with earthquake magnitude. Patterns in rupture complexity arise from a scaling between subevent moment and main event moment. These results can be explained by simple 2‐D dynamic rupture simulations with self‐affine heterogeneity in fault prestress. Applying this to early magnitude estimates, we show that the main event magnitude can be estimated after observing only the first few subevents. |
Julio de 2019 The presence of well‐connected paths is commonly observed in spatially heterogeneous porous formations. Channels consisting of high hydraulic conductivity (K) values strongly affect fate and transport of dissolved species in the subsurface environment. Several studies have established a correlation between connectivity properties of the spatially variable K‐field and solute first arrival times. However, due to limited knowledge of the spatial structure of the K‐field, connectivity metrics are subject to uncertainty. In this work, we utilize the concept of the minimum |
hydraulic resistance and least resistance path to evaluate the connectivity of a K‐field in a stochastic framework. We employ a fast graph theory‐based algorithm to alleviate the computational burden associated with stochastic computations in order to investigate both the impact of the hydrogeological structural conceptualization and domain dimensionality (2‐D vs. 3‐D) on the uncertainty of the minimum hydraulic resistance. Finally, we propose an iterative data acquisition strategy that can be utilized to identify the least resistance path (which is linked to preferential flow channels) in real sites. A synthetic benchmark test is presented, showing the advantages of the proposed sampling strategy when compared to a regular sampling strategy. By using the iterative data sampling strategy, we were able to reduce first arrival time uncertainty by 47% (when compared to the regular sampling strategy), while maintaining site characterization efforts constant. |
Julio de 2019 A modification of a previously introduced electrically small antenna is presented with tuning methods for continuous band coverage for ionospheric heating (~3–10 MHz). Consisting of a small loop antenna inductively coupled to a capacitively loaded loop (CLL), the design may be tuned ±50% of the center of the band by simply adjusting the capacitance of |
the CLL. Abandoning the use of lossy materials for tuning such as solid dielectrics or ferrites, the antenna is greater than 80% efficient across its tuning range. A tenth scale prototype with electromechanical geometry tuning is tested for frequency range and tuning capability especially at the low‐frequency end where port reflection losses tend to dominate. Tuning of the small loop antenna‐CLL coupling is used to mitigate this matching issue, which was demonstrated on the physical antenna model. Experimentally, a tuning range of 33.5–117.5 MHz is achieved with low reflection achievable across the range. |
Julio de 2019 This study quantifies the impact of meteorological variability on the Community Multiscale Air Quality (CMAQ) model‐simulated particulate matter of aerodynamic diameter 2.5 μm or smaller (particulate matter 2.5 [PM2.5]) over the contiguous United States (CONUS). The meteorological variability is represented using the Short‐Range Ensemble Forecast (SREF) produced operationally by the National Oceanic and Atmospheric Administration. A hierarchical cluster analysis technique is applied to down‐select a subset of the SREF members that objectively accounts for the overall meteorological forecast variability of SREF. Three SREF members are selected to drive off‐line CMAQ simulations during January, April, July, and October 2016. Changes in emissions, vertical diffusion, and aerosol processes due to |
meteorological variability dominate changes in aerosol mass concentrations over 55‐73% of the domain except in July when dry deposition dominates emissions and aerosol processes. Weather Research and Forecasting‐Advanced Research WRF (WRF‐ARW) simulations reproduced the variability of surface temperature very well but overestimated the 10‐m wind speed, precipitation, and at some sites the planetary boundary layer height. Averaged over CONUS, CMAQ simulations driven by all three meteorological configurations capture the observed daytime low and nighttime high PM2.5 mass concentrations but underestimated the observed concentrations likely due to faster advection and higher wet deposition in the model. PM2.5 levels across the three simulations agreed well during daytime but showed larger variability during nighttime due to dominance of aerosol, clouds, and advection processes in nighttime. The meteorology‐induced variability in PM2.5 is estimated to be 0.08–24 μg/m3 over the CONUS with larger variability over the eastern United States. |
Julio de 2019 It has long been speculated that biological evolution was influenced by ultraviolet radiation (UVR) reaching the Earth's surface, despite imprecise knowledge of the timing of both UVR flux and evolutionary events. The past strength of Earth's dipole field provides a proxy for UVR flux because of its role in maintaining stratospheric ozone. The timing of Quaternary evolutionary events has become better constrained by fossil finds, improved radiometric dating, use of dung fungi as proxies for herbivore populations, and improved ages for nodes in human phylogeny from human mitochondrial DNA and Y chromosomes. The demise of Neanderthals at ~41 ka can now be closely tied to the intensity |
minimum associated with the Laschamp magnetic excursion, and the survival of anatomically modern humans can be attributed to differences in the aryl hydrocarbon receptor that has a key role in the evolutionary response to UVR flux. Fossil occurrences and dung‐fungal proxies in Australia indicate that episodes of Late Quaternary extinction of mammalian megafauna occurred close to the Laschamp and Blake magnetic excursions. Fossil and dung fungal evidence for the age of the Late Quaternary extinction in North America (and Europe) coincide with a prominent decline in geomagnetic field intensity at ~13 ka. Over the last ~200 kyr, phylogeny based on mitochondrial DNA and Y chromosomes in modern humans yields nodes and bifurcations in evolution corresponding to geomagnetic intensity minima, which supports the proposition that UVR reaching Earth's surface influenced mammalian evolution with the loci of extinction controlled by the geometry of stratospheric ozone depletion. |
Julio de 2019 Quantitative evaluation of earthquake‐induced permeability changes is important for understanding key geological processes, such as advective transport of heat and solute and the generation of elevated fluid pressure. Many studies have independently documented permeability changes in either an aquifer or an aquitard, but the effects of an |
earthquake on both the aquifer and aquitard of the same aquifer system are still poorly understood. In this study, we use the well water‐level response to earth tides and atmospheric pressure to study the changes in hydraulic properties in an aquifer and an overlying confining layer in Beijing, China, following the 11 March 2011 Tohoku earthquake in Japan. Our results show that both the tidal response amplitude and the phase shift increased and that the phase shift changed from negative to positive after the earthquake. We identified increased permeability in both the aquifer and aquitard by the barometric response function method. The horizontal transmissivity of the aquifer increased by a factor of 6, and the vertical diffusivity of the aquitard doubled. |
Julio de 2019 We discuss the question whether inner core (IC) differential rotation or temporal change of the IC surface provides a consistent interpretation for temporal changes of the IC‐related phases and their coda. While temporal change of the IC surface is required and provides a consistent explanation to all the seismic observations, we present three lines of seismic evidence showing that IC differential rotation cannot provide a consistent or reasonable interpretation for the observed temporal change of seismic waves from repeating earthquakes in the South Sandwich Islands (SSI) and the Middle America subduction zone. (1) Changed PKIKP/PKiKP coda between events in a doublet in |
SSI indicates an IC surface scatterer that simply disappeared, with no associated energy in the later event for any assumed IC differential rotation. (2) Within a cluster in SSI, comparisons between temporal changes of PKIKP wave and its coda of the earlier and later event pairs yield contradictory estimates of differential rotation rate change by a factor of at least 27, using different portions of seismic data. (3) The seismic data from repeating earthquakes in Middle America indicate a PKiKP temporal change of 0.017–0.04 s on a timescale of 8–85 days, requiring an unreasonable rotation rate of at least 8.6°/year. We conclude that the observed temporal changes of IC phases are caused by temporal changes of the IC surface, which occur in some localized regions within a timescale of days or months, a phenomenon that should provide important clues to our understanding of core dynamics. |
Junio de 2019 GRACE satellites have detected regional‐scale preseismic, coseismic, and postseismic gravity changes associated with great earthquakes during the GRACE era (2002‐2017). Earthquakes also excite global‐scale transient gravity changes associated with free oscillations that may be discerned for a few days. In this study, we examine such global gravity changes due to Earth's free oscillations and quantify how they affect GRACE measurements. We employ the normal mode formalism to synthesize the global gravity changes after the 2004 Sumatra earthquake and simulate the (gravitational) free oscillation signals manifested in the GRACE K‐band ranging (KBR) measurements. Using the Kaula orbit perturbation theory, we show |
how GRACE inter-satellite distances are perturbed through a complex coupling of eigenfrequencies of the normal modes with the Earth's rotation rate and the GRACE satellites' orbital frequency. It is found that a few gravest normal modes can generate range‐rate perturbations as large as 0.2 μm/s, which are comparable to actual errors of GRACE KBR ranging and accelerometer instruments. Wavelet time‐frequency analysis of the GRACE KBR residual data in December 2004 reveals the existence of a significant transient signal after the 2004 Sumatra earthquake. This transient signal is characterized by a frequency of ~0.022 mHz that could be potentially associated with the largest excitation due to the “football” mode of the Earth's free oscillation. However, the results are also affected by low‐frequency noise of the GRACE accelerometers. Improved space‐borne gravitational instrumentation may open new opportunities to study the Earth's interior and earthquakes independently from global seismological analysis. |
Junio de 2019 Moment tensor (MT) describes shear and tensile motions in the earthquake source. The components of MT are usually assumed to be independent of the frequency. However, this assumption may not satisfy the complex rupture process of induced microearthquakes. We use a novel approach to investigate 984 induced microearthquakes from The Geysers geothermal reservoir in California and find that the retrieved MTs depend on the frequency band of input waveforms. The observed dependence is |
more significant for the components of MT measuring the proportions of seismic energy than for the components determining fault geometry. The component of MT describing shear motion shows a different frequency dependence than that describing tensile motion, suggesting that these two motions occur on the structures with different spatial scales. A subset of seismic events is identified to have a distinct feature of frequency dependence. These events only occur in the layer where the cool water is injected into the hot reservoir and do not migrate downward as the other events. This might be related to the strong thermal effects in the vicinity of injection points that promote the opening of small cracks adjacent to the main fractures. |
Mayo de 2019 Earthquake-induced mass redistribution in the Earth excites the polar motion; its cumulative coseismic effect has been found to cause a secular polar drift (SPD) toward ~140°E longitude with strong statistical tendency. Here we find numerically the cumulatively coseismic effect in SPD since 1952 to be at the rate of ~0.75 mas/year (or ~2.3 cm/year), amounting to nearly 20% of the observed SPD that |
points to the opposite geographical direction and hence is significant in the pursuit of understanding the source budget of SPD. We further argue on theoretical and observational ground that such behavior reflects that of the overall plate tectonic motion and in fact accounts for a fraction of the latter over long term. The exact amount of the fraction is indeterminate until mass transport models of plate tectonics prove adequate. This viewpoint is in contrast to that of Cambiotti et al. which required the coseismic effect to get annihilated completely by the interseismic effect under their earthquake cycle decomposition of the velocity field at the faulting system. |
Mayo de 2019 The earthquakes that make the news are usually the big ones. For example, the magnitude of the 2004 Indian Ocean earthquake that resulted in a quarter million casualties was 9.2. The 1906 San Francisco earthquake was a magnitude 7.9. The catastrophic 2010 Haiti earthquake was a magnitude 7.0. Human-induced earthquakes as large as magnitude 5.8 in Oklahoma have caused some building damage and much public consternation. But below magnitude 3, few people are likely to feel an earthquake, even in populated areas. On page |
767 of this issue, Ross et al. (1) reanalyzed southern California seismic data from 2008 to 2017 with the goal of finding all the earthquakes between magnitude 0.3 and 1.7 that were previously missed. Why put such effort into earthquakes that no one can feel and instruments can barely detect? The answer lies in the frequency of little earthquakes. There are many more little earthquakes than big ones. In most places in the world, there are 10 times as many magnitude 3 earthquakes as magnitude 4 ones, and 10 times as many magnitude 4 earthquakes as magnitude 5 ones, etc. Driving down the minimum magnitude of detection results in many more earthquakes to study. The sheer number of small earthquakes and their frequency make them the key to understanding the sequence of events that stitch together foreshocks, mainshocks, and aftershocks... |
Mayo de 2019 Heat transported from deep within Earth's crust can be used to generate electricity or provide direct heating by circulating fluid through permeable fracture networks in hot rock. Because naturally permeable systems are rare, enhanced geothermal system (EGS) technology stimulates the creation of permeable pathways in otherwise impermeable rock by means of the injection of water under high pressure, creating new fractures and causing preexisting fractures to open. But several EGS |
projects have encountered problems of induced seismicity, particularly the moment magnitude (Mw) 5.5 earthquake in 2017 that occurred near an EGS drill site in Pohang, Republic of Korea (South Korea). Here we explore the implications of, and derive lessons from, the Pohang experience. The Pohang earthquake provides unequivocal evidence that EGS stimulation can trigger large earthquakes that rupture beyond the stimulated volume and disproves the hypothesis that the maximum earthquake magnitude is governed by the volume of injected fluids. Because that hypothesis tacitly underpins hazard-based methods used for managing induced seismicity, those methods must be revised and based on considerations of risk... |
Mayo de 2019 Last week, Marc Chaussidon, director of the Institute of Geophysics in Paris (IPGP), looked at seafloor maps from a recently concluded mission and saw a new mountain. Rising from the Indian Ocean floor between Africa and Madagascar was a giant edifice 800 meters high and 5 kilometers across. In |
previous maps there had been nothing. “This thing was built from zero in 6 months!” Chaussidon says. His team, along with scientists from the French national research agency CNRS and other institutes, had witnessed the birth of a mysterious submarine volcano, the largest such underwater event ever witnessed. “We have never seen anything like this,” says IPGP's Nathalie Feuillet, leader of an expedition to the site by the research vessel Marion Dufresne, which released its initial results last week... |
Mayo de 2019 The 2016 Mw ≥ 6.0 Amatrice-Norcia earthquakes (central Apennines, Italy) and the related seismic sequence were associated with increases in arsenic and vanadium concentrations recorded in groundwater springs a few months before the earthquakes occurred. To evaluate these signals as reliable seismic precursors and effective predictive tools, we studied the geochemical processes that |
caused these anomalies. Using chemical and isotope models, we show that increased concentrations of arsenic and vanadium, a slight increase in boron concentrations, and a concomitant lowering of the boron isotope ratio may be due to mineral desorption (e.g., from iron oxides and/or clays). We argue that a displacing effect on the trace elements sorbed on minerals was triggered by an excess of deep CO2 in groundwater, which occurred prior to the main seismic event as a result of preseismic crustal dilation. Our observations confirm the pivotal role of CO2 in the release of trace elements by alteration of solid phases and provide a new understanding of earthquake-related water chemical anomalies. |
Mayo de 2019 Large earthquakes initiate chains of surface processes that last much longer than the brief moments of strong shaking. Most moderate and large-magnitude earthquakes trigger landslides, ranging from small failures in the soil cover to massive, devastating rock avalanches. Some landslides dam rivers and impound lakes, which can collapse days to centuries later, and flood mountain valleys for hundreds of kilometers downstream. Landslide deposits on slopes can remobilize during heavy rainfall and evolve into debris flows. Cracks and fractures can form and widen on mountain crests and flanks, promoting increased frequency of landslides that lasts for |
decades. More gradual impacts involve the flushing of excess debris downstream by rivers, which can generate bank erosion and floodplain accretion as well as channel avulsions that affect flooding frequency, settlements, ecosystems, and infrastructure. Ultimately, earthquake sequences and their geomorphic consequences alter mountain landscapes over both human and geologic time scales. Two recent events have attracted intense research into earthquake-induced landslides and their consequences: the magnitude M 7.6 Chi-Chi, Taiwan earthquake of 1999, and the M 7.9 Wenchuan, China earthquake of 2008. Using data and insights from these and several other earthquakes, we analyze how such events initiate processes that change mountain landscapes, highlight research gaps, and suggest pathways toward a more complete understanding of the seismic effects on the Earth's surface. |
Mayo de 2019 We address the question of whether all large magnitude earthquakes produce an erosion peak in the subaerial components of fluvial catchments. We evaluate the sediment flux response to the Maule earthquake in the Chilean Andes (Mw 8.8) using daily suspended sediment records from 31 river gauges. The catchments cover drainage areas of 350 to around 10,000 km2, including a wide range of topographic slopes and vegetation cover of the Andean western flank. We compare the 3-8 year post-seismic record of sediment flux to each of the following pre-seismic periods: (1) all pre-seismic data; (2) a 3-year period prior to the seismic event, and (3) the driest pre‐seismic periods, as drought conditions prevailed in the post-seismic period. |
Following the earthquake, no increases in suspended sediment flux were observed for moderate to high percentiles of the streamflow distribution (mean, median and ≥75th percentile). However, more than half of the examined stations showed increased sediment flux during baseflow. By using a Random Forest approach, we evaluate the contributions of seismic intensities, peak ground accelerations, co-seismic landslides, hydroclimatic conditions, topography, lithology and land cover to explain the observed changes in suspended sediment concentration and fluxes. We find that the best predictors are hillslope gradient, low-vegetation cover and changes in streamflow discharge. This finding suggests a combined first‐order control of topography, land cover and hydrology on the catchment-wide erosion response. We infer a reduced sediment connectivity due to the post-seismic drought, which increased the residence time of sediment detached and remobilized following the Maule earthquake |
Mayo de 2019 There is growing interest in nexus research: energy‐water, energy‐water‐land, and more recently food‐energy‐water. Motivating this movement is the recognition that the dynamics and feedbacks that constitute these nexuses have been overlooked in the past but are critical to the planning and management of these interacting elements. Formal reviews have identified gaps in current studies. In this commentary, we highlight additional oversights that are hindering integration of findings in nexus studies, notably usage of imprecise terminology to describe analyses, a failure to close |
the loop by linking production with corresponding waste streams, and exclusion of dynamics linking diverse constituent elements. Equally lacking from current nexus studies is a consistent protocol for communicating the conceptual basis of our studies. To fill this gap, we draw on diverse perspectives and fields to propose a comprehensive and systematic framework that can guide the model conceptualization phase of nexus studies. We also present a standardized documentation practice (similar to one utilized by the agent‐based modeling community) to facilitate communication of nexus studies. These initiatives can improve our ability to account for and communicate the nuanced, food-energy-water nexus interactions in a consistent manner, which is necessary to better inform risk analysis and avoid decisions with unintended consequences and hidden costs to society. |
Mayo de 2019 Earthquakes caused by human activities have been observed for decades. Often these are related to industrial activities pumping fluids into deep geologic formations, like with wastewater disposal. The simplest theory connecting these processes to earthquakes is straightforward: injection leads to fluid pressure changes that either reduce the strength of preexisting faults or generate new faults. In practice, the conditions that lead to induced |
earthquakes are not always clear in ways that can be generalized. Kao et al. (2018, https://doi.org/10.1029/2018GL079288) show how the distribution of induced earthquakes in Western Canada relate to natural rates of deformation in the crust. Using these new results, they discuss an intriguing paradox: induced seismicity can cause short-term increases in the seismic hazard that are followed by a period of reduced seismic hazard. Such hazard-reducing scenarios are plausible but hinge upon simplifying assumptions about how the crust stores and releases strain energy in the form of earthquakes. |
Mayo de 2019 Tidal heating is one of the central processes that generates heat in the interiors of planets and moons, and is in part responsible for the existence of subsurface oceans and geological activity on moons in the outer solar system. Under this process, the amount of heating that occurs varies periodically in time. As a result, we might expect that any geological activity powered by tidal heating, such as volcanic eruptions on Jupiter's tidally-heated |
moon Io, would also vary periodically. Indeed, the water geysers on Saturn's moon Enceladus vary in strength over the course of Enceladus' orbit around Saturn due to tides opening and closing fissures. Io takes only 1.77 days to orbit Jupiter, but its orbit is also slowly changing in time with a period of ~480 days. We compare the variability of Io's volcanoes with the evolution of its orbit, and find that the quasiperiodic behavior of Loki Patera, the most powerful volcano on Io, follows a similar pattern as the orbital changes. We explore whether this volcano could be brightening and fading in response to changes in the amount of heat produced by tides in its interior, and what implications this has for geophysical processes in Io's interior. |
Mayo de 2019 Society's progress along the four corners of prepare, adsorb, respond and adapt resilience square is uneven, in spite of our understanding of the foundational science and a growing sense that urgent action is needed. The resilience vignettes |
describe the meaning and impact of current and near-term change in four major domains: human health impacts from air pollution, coastal inundation from sea-level rise, damaging earthquakes in populated areas, and impacts from extreme precipitation. Given our understanding of the scientific principles, societal action, from preparation to adaption, will be critical in minimizing the negative impacts of today's changes. The unprecedented rates of change in today's Earth system argue for urgent action in support of a resilient global society. |
Mayo de 2019 The size or energy of diverse structures or phenomena in geoscience appears to follow power‐law distributions. A rigorous statistical analysis of such observations is tricky, though. Observables can span several orders of magnitude, but the range for which the power law may be valid is typically truncated, usually because the smallest events are too tiny to be detected and the largest ones are limited by the system size. |
long-term hazard. After reviewing the theoretical background for power-law distributions, we improve an objective statistical fitting method and apply it to diverse data sets. The method is described in full detail and it is easy to implement. Our analysis elucidates the range of validity of the power-law fit and the corresponding exponent, and whether a power-law tail is improved by a truncated log-normal. We confirm that impact fireballs and Californian earthquakes show untruncated power-law behavior, whereas global earthquakes follow a double power law. Rain precipitation over space and time and tropical cyclones show a truncated power-law regime. Karst sinkholes and wildfires, in contrast, are better described by truncated log-normals, although wildfires also may show power-law regimes. Our conclusions only apply to the analyzed data sets, but show the potential of applying this robust statistical technique in the future. |
Mayo de 2019 Short-period gravity waves are ubiquitous in the mesosphere, but the vertical structures of their perturbations are difficult to observe. The Jicamarca 50‐MHz VHF radar allows observations of winds and turbulent scatter with high temporal and vertical resolution. We present a case of a quasi-monochromatic gravity wave with period 520 (±40) seconds that is likely ducted below a southward wind jet between 68 and 74 km. Above this layer of evanescence, a northward wind enables it to emerge into a more stable layer, where it is |
refracted to a short vertical wavelength of (2.2 ± 0.2) km; data shows evidence of weak nonlinearity, and possible overturning or partial reflection from higher altitudes, above the observable region, in the form of standing wave structure in vertical velocity - 75 km. Based on the dispersion relation, and with help of a two-dimensional model, we determine that most likely the wave is propagating northward and is being ducted below and tunneling through the regions of evanescence created by the wind flow and typical mesospheric thermal structure. This is the first time that such an event has been identified in the Jicamarca mesospheric echoes, and it is distinct from Kelvin-Helmholtz billows also commonly seen with this sensitive radar – instead apparently revealing tunneling of the gravity wave through ambient winds. |
Mayo de 2019 The Milky Way Galaxy teems with planetary systems, most of which are unlike our own. It is tempting to assume that life can only originate on a planet that is similar to Earth, but different kinds of planets may be able to sustain Earth-like features that could be important for habitability. To focus the search for extraterrestrial life, scientists must assess which features of Earth are essential to the development and sustenance of life for billions of years and whether the formation of such planets is common. External effects such as stellar variability and orbital stability can affect habitability, but internal planetary processes that sustain a clement surface are |
essential to life; these processes are, however, difficult to characterize remotely. A combination of observations, experiments, and modeling are needed to understand the role of planetary interiors on habitability and guide the search for extraterrestrial life. As exoplanet detection techniques improve, Earth-sized planets are likely to be found in the radiative habitable zone, that is, at distances from their host stars where they could have temperate (about 0° to 100°C) surface temperatures. This is important because to be habitable, a planet must be able to buffer life from extreme (globally sterilizing) variations in temperature. Launched in 2018, NASA's Transiting Exoplanet Survey Satellite has the capability to find small planets in the habitable zone of nearby stars and measure their radii. |
Mayo de 2019 Double seismic zones are ubiquitous features of subduction zones, where seismicity is distributed along two layers separated by a region with significantly less seismic activity. Dehydration embrittlement is thought to be responsible for earthquakes in the subducting crust (upper layer), but the case for it in the lithospheric mantle (lower layer) is less clear. We apply a recently developed |
relative relocation technique to characterize seismicity in 32 slab segments. The high‐precision hypocentral depths allow us to assign events to either the upper or lower layer and to separately estimate frequency size distributions for each plane. We find consistently larger b values, correlating with slab age, for the upper layer and roughly constant values for the lower. We also show that thermal parameter and plate age are the key controls on double seismic zone geometry. Our results point to a relatively dry lower layer and suggest a fundamentally different mechanism for lithospheric mantle earthquakes. |
Mayo de 2019 We conduct finite element analysis to investigate the effect of sharp topography on surface ground deformation caused by pressure changes in a magma reservoir. Tilt data express the horizontal gradient of vertical displacement and therefore can emphasize small variations in deformation that go unnoticed using other methods. We find that the |
vertical displacement profile at a surface with a cliff can be thought of as the superposition of the deformation from shallow and deeper sources. This combination can create a small peak in vertical displacement that acts as a pseudo-source, creating a reversal of the deformation gradient and therefore anomalous tilt magnitude and a rotation of up to 180°. We apply these models to Kīlauea Caldera and find that surface geometry creates a tilt rotation of 10°, partially explaining anomalous tilt that has been observed. Our analysis highlights the importance of considering topography when assessing tilt measurements at active volcanoes. |
Abril de 2019 Despite the global significance of the subsurface biosphere, the degree to which it depends on surface organic carbon (OC) is still poorly understood. Here, we compare stable and radiogenic carbon isotope compositions of microbial phospholipid fatty acids (PLFAs) with those of in situ potential microbial C sources to assess the major C sources for subsurface microorganisms in biogeochemical distinct shallow aquifers (Critical Zone Exploratory, Thuringia Germany). Despite the presence of younger OC, the microbes assimilated 14C free OC to varying degrees; ~31% in groundwater within the oxic zone, ~47% in an iron reduction zone, and ~70% in a sulfate reduction/anammox zone. The persistence of trace amounts of mature and partially biodegraded |
hydrocarbons suggested that autochthonous petroleum‐derived hydrocarbons were a potential 14C‐free C source for heterotrophs in the oxic zone. In this zone, Δ14C values of dissolved inorganic carbon (−366 ± 18‰) and 11MeC16:0 (−283 ± 32‰), an important component in autotrophic nitrite oxidizers, were similar enough to indicate that autotrophy is an important additional C fixation pathway. In anoxic zones, methane as an important C source was unlikely since the 13C fractionations between the PLFAs and CH4 were inconsistent with kinetic isotope effects associated with methanotrophy. In the sulfate reduction/anammox zone, the strong 14C depletion of 10MeC16:0 (−942 ± 22‰), a PLFA common in sulfate reducers, indicated that those bacteria were likely to play a critical part in 14C free sedimentary OC cycling. Results indicated that the 14C content of microbial biomass in shallow sedimentary aquifers results from complex interactions between abundance and bioavailability of naturally occurring OC, hydrogeology, and specific microbial metabolisms. |
Abril de 2019 Long‐term seismic monitoring networks are well positioned to leverage advances in machine learning because of the abundance of labeled training data that curated event catalogs provide. We explore the use of convolutional and recurrent neural networks to accomplish discrimination of explosive and tectonic sources for local distances. Using a 5 |
year event catalog generated by the University of Utah Seismograph Stations, we train models to produce automated event labels using 90‐s event spectrograms from three‐component and single‐channel sensors. Both network architectures are able to replicate analyst labels above 98%. Most commonly, model error is the result of label error (70% of cases). Accounting for mislabeled events (~1% of the catalog) model accuracy for both models increases to above 99%. Classification accuracy remains above 98% for shallow tectonic events, indicating that spectral characteristics controlled by event depth do not play a dominant role in event discrimination. |
Abril de 2019 Geodetic analysis of radio tracking measurements of the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft while in orbit about Mercury has yielded new estimates for the planet's gravity field, tidal Love number, and pole coordinates. The derived right ascension (α = 281.0082° ± 0.0009°; all uncertainties are 3 standard deviations) and declination (δ = 61.4164° ± 0.0003°) of the spin pole place Mercury in the Cassini state. Confirmation of the equilibrium state with an estimated mean (whole planet) obliquity ϵ of 1.968 ± 0.027 arcmin enables the confident determination of the planet's normalized polar moment of inertia (0.333 ± 0.005), which indicates a high degree of internal differentiation. Internal |
structure models generated by a Markov Chain Monte Carlo process and consistent with the geodetic constraints possess a solid inner core with a radius (ric) between 0.3 and 0.7 that of the outer core (roc). |
Abril de 2019 The subduction zone of central Chile (36°S) has produced some of the world's largest earthquakes and significant volcanic eruptions. Understanding the fluid fluxes and structure of the subducting slab and overriding plate can provide insight into the tectonic processes responsible for both seismicity and magmatism. Broadband and long‐period magnetotelluric data were collected along a 350‐km profile in central Chile and Argentina and show a regional geoelectric strike of 15 ± 19° east of north. The preferred two‐dimensional inversion model included the geometry of the subducting Nazca plate as a constraint. On the upper surface of the Nazca plate, conductors were interpreted as |
fluids expelled from the downgoing slab via compaction at shallow depth (C1) and metamorphic reactions at depths of 40–90 km (C2 and C3). At greater depths (130 km), a conductor (C7) is interpreted as a region of partial melt related to deserpentinization in the backarc. A resistor on the slab interface (R1) is coincident with a high‐velocity anomaly which was interpreted as a strong asperity which may affect the coseismic slip behavior of large megathrust earthquakes at this latitude. Correlations with seismicity suggest slab fluids alter the forearc mantle and define the downdip limit of the seismogenic zone. Beneath the volcanic arc, several upper crustal conductors (C4 and C5) represent partial melt beneath the Tatara‐San Pedro Volcano and the Laguna del Maule Volcanic Field. A deeper lower crustal conductor (C6) underlies both volcanoes and suggests a connected network of melt in a thermally mature lower crust. |
Abril de 2019 We develop a game theoretic model of the role of foresight in games involving users interacting over a public good. Previous research in this area has applied game theory to understand social dilemmas and inform policy initiatives. However, considerations of the “evolving structure” of natural resource games over time and agents' planning horizon raises the complexity of game analysis substantially and has often been overlooked. We |
analyze a simple model of an irrigation system shared by two users and consider how players will act under different levels of foresight. Without foresight into game changes over time, players are blind to the fact that they are in a game of chicken. We model agents with foresight by interconnecting games across time and show how this creates opportunities for “strategic loss” early on, allowing players with foresight to reduce total costs. High future costs can thus be avoided with foresight if the rising costs of inaction are made apparent. We consider the effect of discounting and differences between players to provide policy recommendations regarding incentives for foresight. |
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