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Abril de 2019 Modeling injection-induced earthquakes requires coupling porous media flow, rock mechanics, and fault friction. Highly nonlinear laboratory derived constitutive laws for fault friction pose a major challenge for computational models that couple flow and geomechanics. We present a finite element formulation to simulate injection induced earthquake sequences in rate‐and‐state faults embedded in poroelastic media. We simulate all phases of the stick slip cycle: from fault reactivation as pressure accumulates near the fault, to earthquake nucleation phase, coseismic rupture propagation and interseismic periods. Our simulations are quasi dynamic: we neglect inertia, and adopt the so called radiation damping approximation. We perform validation and |
verification tests based on a simple spring‐block analog that allows straightforward comparison between our 2 D finite element model and the single degreeof freedom dynamics. We also verify our frictional contact algorithm by simulating injection‐induced earthquakes on a slip‐weakening strike slip fault. We finally study the impact of different rate‐and‐state laws (aging and slip laws), as well as the role of the degree of poroelastic coupling, by varying the Biot coefficient. We characterize the undrained pressure response triggered by the fast propagation of rupture fronts. Undrained pressure changes during rupture act as an additional coseismic weakening mechanism, controlling the propagation or arrest of the rupture fronts. We find that this feedback between pore pressure and slip propagation, which is absent in uncoupled simulations, leads to distinctively asymmetric rupture patterns in induced earthquakes in poroelastic media. Our results show that capturing the coupling between fault frictional processes and rock poroelastic behavior requires well resolved and fully coupled simulations. |
Abril de 2019 A versatile, low-cost way to study Earth's interior from sea has yielded its first images and is scaling up. By deploying hydrophones inside neutrally buoyant floats that drift through the deep ocean, seismologists are detecting earthquakes that occur below the sea floor and using the acoustic signals to peer inside Earth in places where data have been lacking. In February, a team of researchers reported using nine of these floats near the Galápagos |
Islands to trace a mantle plume—a massive column of hot rock that rises up from thousands of kilometers below the islands. The floats, called MERMAIDs (mobile earthquake recorders in marine areas by independent divers), have since been redesigned for longer life, and 18 are searching for plumes in the waters around Tahiti, the team reported last week at the annual meeting of the European Geosciences Union. This August, another 30 MERMAIDs will be added to the South Pacific project. MERMAIDs could be a general purpose tool for ocean observations, as well. The hydrophones can also detect the sound of rain or whales, and MERMAIDs can be outfitted with other environmental or biological sensors. |
Abril de 2019 Crustal magma chambers can grow to be hundreds to thousands of cubic kilometers, potentially feeding catastrophic caldera‐forming eruptions. Smaller volume chambers are expected to erupt frequently and freeze quickly; a major outstanding question is how magma chambers ever grow to the sizes required to sustain the largest eruptions on Earth. We use a thermo‐mechanical model to investigate the primary factors that govern the extrusive:intrusive ratio in a chamber, and how this relates to eruption frequency, eruption size, and long‐term chamber growth. The model consists of three fundamental timescales: the magma injection timescale τin, the cooling timescale τcool, and the timescale for |
viscous relaxation of the crust τrelax. We estimate these timescales using geologic and geophysical data from four volcanoes (Laguna del Maule, Campi Flegrei, Santorini, and Aso) to compare them with the model. In each of these systems, τin is much shorter than τcool and slightly shorter than τrelax, conditions that in the model are associated with efficient chamber growth and simultaneous eruption. In addition, the model suggests that the magma chambers underlying these volcanoes are growing at rates between ~10−4 and 10−2 km3/year, speeding up over time as the chamber volume increases. We find scaling relationships for eruption frequency and size that suggest that as chambers grow and volatiles exsolve, eruption frequency decreases but eruption size increases. These scaling relationships provide a good match to the eruptive history from the natural systems, suggesting that the relationships can be used to constrain chamber growth rates and volatile saturation state from the eruptive history alone. |
Abril de 2019 The lithospheric structure of Antarctica is still underexplored. Moho depth estimate studies are in disagreement by more than 10 km in several regions, including, for example, the hinterland of the Transantarctic Mountains. Taking account the sparseness of seismological stations and the nonuniqueness of potential field methods, inversions of Moho depth are performed here based on satellite gravity data in combination with currently available seismically constrained Moho depth estimates. Our results confirm that a lower density contrast at the Moho is present under East Antarctica than beneath West Antarctica. A comparison between the Moho depth derived from our inversion and an Airy isostatic Moho model also reveals a spatially variable buoyancy contribution |
from the lithospheric mantle beneath contrasting sectors of East Antarctica. Finally, to test the plausibility of different Moho depths scenarios for the Transantarctic Mountains‐Wilkes Subglacial Basin system, we present 2D lithospheric models along the Trans‐Antarctic Mountain Seismic Experiment/Gamburtsev Mountain Seismic experiment seismic profile. Our models show that if a moderately depleted lithospheric mantle of inferred Proterozoic age underlies the region, then a shallower Moho is more likely beneath the Wilkes Subglacial Basin. If however, refertilization processes occurred in the upper mantle, for example, in response to Ross age subduction, then a deeper Moho scenario is preferred. We conclude that 3D lithospheric modeling, coupled with the availability of new seismic information in the hinterland of the Transantarctic Mountains, is required to help resolve this controversy, thereby also reducing the ambiguities in geothermal heat flux estimation beneath this key part of the East Antarctic Ice Sheet. |
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 over riding 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 down‐going 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 de serpentinization in the back arc. 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 co seismic slip behavior of large megathrust earthquakes at this latitude. Correlations with seismicity suggest slab fluids alter the forearc mantle and define the down‐dip 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 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 pre existing 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. 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 |
Abril de 2019 After extensive development of the dislocation theorem regarding static deformations that are due to earthquakes, co‐seismic deformations can be well explained by the present elastic dislocation theorem. However, it is difficult to separate and interpret the contributions from inter‐seismic and post‐seismic deformations, because various mechanisms are involved, including the coupling of the fault interface, aftershock activity, porous‐elastic rebound, and viscoelastic relaxation. It is only possible to infer the dominant mechanism for an earthquake via multi‐observation of post seismic deformations in regions that have a dense geodetic |
network. Accurately simulating a process in a realistic Earth model is a unique way to overcome this difficulty. Here, we present a new robust, accurate, and anti‐oscillational method for modelling the post‐seismic deformations that are due to viscoelastic relaxation in a realistic gravitational spherical Earth model with linear viscoelastic rheological models. The viscoelastic dislocation Love numbers (DLNs) are evaluated by comparing the results of Sun & Okubo (1993), those of Tanaka et al. (2006, 2007), and our newly derived analytical results. The satisfactory consistency between our new results and previous ones demonstrates that our proposed method is highly accurate. This robust and accurate forward modelling approach is helpful for investigating and separating the major mechanism of the post‐seismic deformations and will greatly benefit the inverse investigation of the ground viscoelastic parameters from geodetic observations. |
Abril de 2019 Earthquake radiation is broadband, and its temporal evolution carries the seismic signature of the rupture process. I use established and develop new observational metrics to quantify the temporal variation in radiated energy (seismic power) and in a time- dependent scaled radiated energy. Universal functional forms of moment rate, seismic power, |
and scaled energy arise from a global database of source time functions. Earthquakes radiate mostly and most efficiently in the early stage of development of the rupture that is in the first 10–30% of the overall rupture duration. This result is independent of earthquake magnitude, depth, and focal mechanism. Beyond depth dependence in elastic properties with depth that explain variations in source duration and radiated energy, subtle differences in functional forms exist between shallow and deep earthquakes. Deep events have a slower development than shallow earthquakes, but they carry a higher peak in seismic power. |
Marzo de 2019 Automating geoscience analysis |
Understanding the behavior of Earth through the diverse fields of the solid Earth geosciences is an increasingly important task. It is made challenging by the complex, interacting, and multiscale processes needed to understand Earth’s behavior and by the inaccessibility of nearly all of Earth’s subsurface to direct observation. Substantial increases in data availability and in the increasingly realistic character of computer simulations hold promise for accelerating progress, but developing a deeper understanding based on these capabilities is itself challenging. Machine learning will play a key role in this effort. We review the state of the field and make recommendations for how progress might be broadened and accelerated. |
Marzo de 2019 A study published this week offers some of the best evidence yet that humans, like many other creatures, can sense Earth's magnetic field. But it doesn't settle other questions that have swirled around this contentious idea for decades: If we do have a subconscious magnetic sense, do we ever use it? |
And does it arise from an iron mineral found in our brains, as the authors believe? The experiment recorded brain activity from electrodes on the scalp to search 34 participants for some response to changes in a highly controlled magnetic field equal in strength to Earth's. It revealed a marked change in brain waves of a certain frequency. But some researchers aren't convinced that the brain's reaction to a magnetic field represents a true "sense" unless this reaction also guides our behavior. |
Marzo de 2019 We monitor dynamic rupture propagation during laboratory stick‐slip experiments performed on saw‐cut Westerly granite under upper crustal conditions (10‐90 MPa). Spectral analysis of high‐frequency acoustic waveforms provided evidence that energy radiation is enhanced with stress conditions and rupture velocity. Using acoustic recordings bandpass filtered to 400‐800 kHz (7 - 14 mm wavelength) and highpass filtered |
above 800 kHz, we back projected high frequency energy generated during rupture propagation. Our results show that the high frequency radiation originates behind the rupture front during propagation and propagates at a speed close to that obtained by our rupture velocity inversion. From scaling arguments, we suggest that the origin of high frequency radiation lies in the fast dynamic stress drop in the breakdown zone together with off fault co seismic damage propagating behind the rupture tip. The application of the back‐projection method at the laboratory scale provides new ways to locally investigate physical mechanisms that control high frequency radiation. |
Marzo de 2019 The Laguna del Maule (LdM) volcanic field comprises the greatest concentration of postglacial rhyolite in the Andes and includes the products of ~40 km3 of explosive and effusive eruptions. Recent observations at LdM by interferometric synthetic aperture radar and global navigation satellite system geodesy have revealed inflation at rates exceeding 20 cm/year since 2007, capturing an ongoing period of growth of a potentially large upper crustal magma reservoir. Moreover, magnetotelluric and gravity studies indicate the presence of fluids and/or partial melt in the upper crust near the center of inflation. Petrologic observations imply repeated, |
rapid extraction of rhyolitic melt from crystal mush stored at depths of 4–6 km during at least the past 26 ka. We utilize multiple types of surface wave observations to constrain the location and geometryof low velocity domains beneath LdM. We present a three dimensional shear wave velocity model that delineates a ~450 km3 shallow magma reservoir ~2 to 8 km below surface with an average melt fraction of ~5%. Interpretation of the seismic tomography in light of existing gravity, magnetotelluric, and geodetic observations supports this model and reveals variations in melt content and a deeper magma system feeding the shallow reservoir in greater detail than any of the geophysical methods alone. Geophysical imaging of the LdM magma system today is consistent with the petrologic inferences of the reservoir structure and growth during the past 20–60 kyr. Taken together with the ongoing unrest, a future rhyolite eruption of at least the scale of those common during the Holocene is a reasonable possibility. |
Marzo de 2019 Advances in geodetic techniques enable us to detect “slow‐earthquake” transients (e.g., slow‐slip events, SSEs) with improving accuracy and coverage. Recent observations reveal intriguing changes of SSE behavior before and/or after earthquakes. However, the physics behind these observations remain largely unknown. How does SSE pattern change during megathrust earthquake super‐cycle? How do SSEs respond to “external” tectonic perturbations such as stress perturbation from earthquakes, or nontectonic forces such as tidal modulation and seasonal loading? Can SSE pattern changes shed light on the onset of a large earthquake? To address these questions, we employ laboratory‐based rate‐and‐state frictional |
law on subduction zone faults with realistic frictional” properties incorporating megathrust earthquake and SSE regions. We conduct 2‐D/3‐D quasi‐dynamic earthquake cycle simulations to study the “intrinsic SSE pattern changes as how it evolves at different stages of the earthquake cycle, versus the changes in SSE pattern responding to external stress perturbations. Our results suggest that, despite both intrinsic and perturbation models are capable to introduce large variability in SSE pattern, there are considerable observable characteristics that can be used to differentiate these two models. Without external perturbation the SSE patterns change intrinsically during the super‐cycle. The recurrence interval and peak slip rate of SSEs decrease significantly right before megathrust earthquake and could be used as a potential warning sign. Whereas SSE patterns can vary significantly when perturbed by an earthquake or other tectonic/nontectonic sources. Recurring SSEs can be advanced or delayed by external perturbations, and multiple SSEs can be affected if perturbation is long lasting. |
Marzo de 2019 The magnitude of great subduction megathrust earthquakes is controlled mainly by the number of adjacent asperities failing synchronously and the resulting rupture length. Here we investigate experimentally the long‐term recurrence behavior of a pair of asperities coupled by static stress transfer over hundreds of seismic cycles. We statistically analyze long (c. 500 ka) time‐series of M8‐9 analogue earthquakes simulated using a seismotectonic scale model approach with two aims: First, to constrain probabilistic measures (frequency‐size distribution, variability) useful for |
hazard assessment and, second, to relate them with geometric observables (coseismic slip pattern, locking pattern). We find that the number of synchronized asperity failures relative to the number of individual asperity failures as well as the coefficients of variation of recurrence intervals and seismic moment scale with the logarithm of stress coupling between the asperities. Accordingly, tighter packed asperities tend to recur more periodically and with a more characteristic magnitude while more distant asperities show clustering of more variable sized events. The probability of synchronized failures seems to be controlled to first order by geometrical relations (i.e. spacing and offset of asperities. The effects of rheological properties are evident but it remains to be explored to which extent they vary in nature and how sensitive the system is to those. |
Marzo de 2019 We estimate time‐independent earthquake likelihoods in central Los Angeles using a model of interseismic strain accumulation and the 1932–2017 seismic catalog. We assume that on the long‐term average, earthquakes and aseismic deformation collectively release seismic moment at a rate balancing interseismic loading, mainshocks obey the Gutenberg‐Richter law (a log linear |
magnitude‐frequency distribution [MFD]) up to a maximum magnitude and a Poisson process, and aftershock sequences obey the Gutenberg‐Richter and “Båth” laws. We model a comprehensive suite of these long‐term systems, assess how likely each system would be to have produced the MFD of the instrumental catalog, and use these likelihoods to probabilistically estimate the long‐term MFD. We estimate Mmax = 6.8 + 1.05/−0.4 (every ~300 years) or Mmax = 7.05 + 0.95/−0.4 assuming a truncated or tapered Gutenberg‐Richter MFD, respectively. Our results imply that, for example, the (median) likelihood of one or more Mw ≥ 6.5 mainshocks is 0.2% in 1 year, 2% in 10 years, and 18–21% in 100 years. |
Marzo de 2019 Traditionally, groundwater and surface water flow models have been calibrated against two observation types: hydraulic heads and surface water discharge. It has repeatedly been demonstrated, however, that these classical observations do not contain sufficient information to calibrate flow models. To reduce the predictive uncertainty of flow models, the consideration of other observation types constitutes a promising way forward. Despite the ever-increasing availability of other observation types, however, they are still unconventional when it comes to flow model calibration. By reviewing studies that included non-classical observations in flow model calibration, benefits and challenges associated with their |
integration in flow model calibration were identified and their information content analyzed. While explicit simulation of mass transport processes in flow models poses challenges, even simplified approaches to integrate tracer concentrations yield significantly better calibration results than using only classical observations. For a majority of calibrated flow models, observations of tracer concentrations and of exchange fluxes were beneficial. Temperature observations improved the simulation of heat transport but often worsened all other model outcomes. Only when temperature observations were made within 2 m of the surface water groundwater interface did they have the potential to also improve flow and mass transport simulations. Surprisingly, many models were calibrated manually rather than with the widely available, mathematically robust and automated tools. There is a clear need for more systematic implementation of unconventional observations and automated flow model calibration as well as for more systematic quantification of the information content of unconventional observations. |
Marzo de 2019 We estimate time‐independent earthquake likelihoods in central Los Angeles using a model of interseismic strain accumulation and the 1932-2017 seismic catalog. We assume that on the long-term average, earthquakes and aseismic deformation collectively release seismic moment at a rate balancing interseismic loading, mainshocks obey the Gutenberg Richter law (a log-linear magnitude |
frequency distribution (MFD)) up to a maximum magnitude and a Poisson process, and aftershock sequences obey the Gutenberg-Richter and “Bâth” laws. We model a comprehensive suite of these long term systems, assess how likely each system would be to have produced the MFD of the instrumental catalog, and use these likelihoods to probabilistically estimate the long-term MFD. We estimate Mmax=6.8 +1.05/ 0.4 (every ~300 years) or Mmax=7.05 +0.95/ 0.4 assuming a truncated or tapered Gutenberg Richter MFD, respectively. Our results imply that, for example, the (median) likelihood of a Mw≥6.5 mainshock is 0.2% in one year, 2% in 10 years, and 18-21% in 100 years. |
Marzo de 2019 The Laguna del Maule (LdM) volcanic field comprises the greatest concentration of post-glacial rhyolite in the Andes, and includes the products of ~40 km3 of explosive and effusive eruptions. Recent observations at LdM by InSAR and GPS geodesy have revealed inflation at rates exceeding 20 cm/yr since 2007, capturing an ongoing period of growth of a potentially large upper crustal magma reservoir. Moreover, magnetotelluric and gravity studies indicate the presence of fluids and/or partial melt in the upper crust near the center of inflation. Petrologic observations imply repeated, rapid extraction of rhyolitic melt from crystal mush stored at depths of 4-6 km during at least the past 26 ka. We utilize multiple types of surface |
wave observations to constrain the location and geometry of low velocity domains beneath LdM. We present a 3D shear-wave velocity model that delineates a ~450 km3 shallow magma reservoir (~2 to 8 km below surface) with an average melt fraction of ~5%. Interpretation of the seismic tomography in light of existing gravity, magnetotelluric, and geodetic observations supports this model and reveals variations in melt content and a deeper magma system feeding the shallow reservoir in greater detail than any of the geophysical methods alone. Geophysical imaging of the LdM magma system today is consistent with the petrologic inferences of the reservoir structure and growth during the past 20-40 kyr. Taken together with the ongoing unrest, a future rhyolite eruption of at least the scale of those common during the Holocene is a reasonable possibility. |
Marzo de 2019 Crustal magma chambers can grow to be hundreds to thousands of cubic kilometers, potentially feeding catastrophic caldera-forming eruptions. Smaller-volume chambers are expected to erupt frequently and freeze quickly; a major outstanding question is how magma chambers ever grow to the sizes required to sustain the largest eruptions on Earth. We use a thermo‐mechanical model to investigate the primary factors that govern the extrusive:intrusive ratio in a chamber, and how this relates to eruption frequency, eruption size, and long‐term chamber growth. The model consists of three fundamental timescales: the magma injection timescale τin, the cooling timescale τcool, and the timescale for viscous relaxation of the |
crust τrelax. We estimate these timescales using geologic and geophysical data from four volcanoes (Laguna del Maule, Campi Flegrei, Santorini, Aso) to compare them with the model. In each of these systems, τin is much shorter than τcool and slightly shorter than τrelax, conditions that in the model are associated with efficient chamber growth and simultaneous eruption. In addition, the model suggests that the magma chambers underlying these volcanoes are growing at rates between ~10‐4-10‐2 km3/yr, speeding up over time as the chamber volume increases. We find scaling relationships for eruption frequency and size that suggest that as chambers grow and volatiles exsolve, eruption frequency decreases but eruption size increases. These scaling relationships provide a good match to the eruptive history from the natural systems, suggesting the relationships can be used to constrain chamber growth rates and volatile saturation state from the eruptive history alone. |
Febrero 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 |
Febrero de 2019 Despite the growing spatiotemporal density of geophysical observations at subduction zones, predicting the timing and size of future earthquakes remains a challenge. Here we simulate multiple seismic cycles in a laboratory-scale subduction zone. The model creates both partial and full margin ruptures, simulating magnitude Mw 6.2– 8.3 |
earthquakes with a coefficient of variation in recurrence intervals of 0.5, similar to real subduction zones. We show that the common procedure of estimating the next earthquake size from slip‐deficit is unreliable. On the contrary, machine learning predicts well the timing and size of laboratory earthquakes by reconstructing and properly interpreting the spatiotemporally complex loading history of the system. These results promise substantial progress in real earthquake forecasting, as they suggest that the complex motion recorded by geodesists at subduction zones might be diagnostic of earthquake imminence |
Febrero de 2019 Earthquake (EQ) prediction is an essential topic in recent geophysics and disaster management. In order to explain EQ precursory phenomena, especially the ionospheric perturbations, a few hypotheses have been proposed as the mechanism of lithosphere-atmosphere-ionosphere coupling. The most reliable seems to be the atmospheric gravity wave (AGW) hypothesis, because a lot of subionospheric very low frequency (VLF) observations and also ground surface measurements support this hypothesis. However, no direct signature of AGW activity in the middle atmosphere has been yet obtained. So in this study, we have used the ERA5 reanalysis data to investigate the tempo-spatial evolution of stratospheric AGW activity before a recent huge seismic event of the 2016 |
Kumamoto EQ on 15 April (Mw7.2). It was found that the AGW potential energy is enhanced significantly during about 1 week before the EQ. The enhancement was mainly distributed around the EQ epicenter and expanded toward eastern Japan. The AGW activity was highest around 11 April, then it calmed down and returned to the background level right before the EQ. These results were compared with the subionospheric VLF observations during the same period, and then the tempo-spatial evolutions of the lower ionospheric perturbation are found to be very consistent with the stratospheric behavior. The present paper reports on the first finding that the abnormal AGW activity in the stratosphere is detected before a major EQ, and the coincidence of stratospheric AGW activity with VLF subionospheric perturbations provides further support to the AGW hypothesis of the lithosphere- atmosphere-ionosphere coupling process. |
Febrero de 2019 Earthquake radiation is broadband and its temporal evolution carries the seismic signature of the rupture process. I use established and develop new observational metrics to quantify the temporal variation in radiated energy (seismic power) and in a time-dependent scaled radiated energy. Universal functional forms of moment rate, seismic power, and scaled energy arise from a global database of source |
time functions. Earthquakes radiate mostly and most efficiently in the early stage of development of the rupture that is in the first 10-30% of the overall rupture duration. This result is independent of earthquake magnitude, depth, and focal mechanism. Beyond depth-dependence in elastic properties with depth that explain variations in source duration and radiated energy, subtle differences in functional forms exist between shallow and deep earthquakes. Deep events have a slower development than shallow earthquakes but they carry a higher peak in seismic power. |
Febrero de 2019 Light‐toned layered deposits rich in sulfates are widespread on Mars in several locations. Understanding how these deposits formed is crucial to infer the climatic conditions during Martian history and, in light of the fact that potentially similar deposits on Earth have been shown to be conducive to bacterial life, is critical in the search for habitable environments on Mars.We focused on Kotido crater because it shows a remarkable infill and excellent data coverage. We drew a detailed geological map, recognizing sub-units interbedded within the |
layered deposits: light-toned and darker-toned layers, subconical mounds and associated fractures. We interpret these materials to result from episodes of water upwelling sourced from the subsurface: a mixture of fluids, gases and sediments emerged in Kotido leading to the deposition of the different sub‐units depending on the relative ratio of the upwelling materials in the different phases. The mounds and fractures would represent the morphological expression of the upwelling process, while the light‐ and darker-toned material would represent the resulting deposits. The proposed mechanism is identical to that of terrestrial environments such as playa and spring deposition typical of arid settings where bacterial life is well adapted. |
Febrero de 2019 The geological rupture responsible for the devastating magnitude-7.5 earthquake that struck Palu, Indonesia, in September 2018 ripped through Earth's crust at rare high speed, scientists report. This "supershear" behavior likely intensified the shaking in the quake, which triggered a tsunami and |
killed more than 2000 people. Typically, the ruptures that cause earthquakes travel at a speed slower than its damaging side-to-side waves, called shear waves. In the past 2 decades, however, seismologists have discovered a handful of high-speed ruptures on long, linear, and smooth strike-slip faults. The Palu rupture, however, occurred on a rougher strike-slip fault, with kinks in its path, raising fears that far more regions could be at risk of high-speed quakes than once thought. |
Febrero de 2019 |
April (Mw7.0). It was found that the AGW potential energy is enhanced significantly during about one week before the EQ. The enhancement was mainly distributed around the EQ epicenter and expanded toward eastern Japan. The AGW activity was highest around 11 April, then it calmed down and returned to the background level right before the EQ. These results were compared with the subionospheric VLF observations during the same period, and then the tempo-spatial evolutions of the lower ionospheric perturbation are found to be very consistent with the stratospheric behavior. The present paper reports on the first finding that the abnormal AGW activity in the stratosphere is detected before a major EQ, and the coincidence of stratospheric AGW activity with VLF subionospheric perturbations provides further support to the AGW hypothesis of the LAIC process. |
Febrero de 2019 The scale of groundwater upwelling on Mars, as well as its relation to sedimentary systems, remains an ongoing debate. Several deep craters (basins) in the northern equatorial regions show compelling signs that large amounts of water once existed on Mars at a planet wide scale. The presence of water formed features, including fluvial Gilbert and sapping deltas fed by sapping valleys, constitute strong evidence of groundwater upwelling resulting in long term standing bodies of water inside the basins. Terrestrial field evidence shows that sapping valleys can occur in basalt bedrock and not only in unconsolidated sediments. A hypothesis which considers the elevation differences between the observed |
morphologies and the assumed basal groundwater level is presented and described as the "dike confined water" model, already present on Earth and introduced for the first time in the Martian geological literature. Only the deepest basins considered in this study, those with bases deeper than 4000 m in elevation below the Mars datum, intercepted the water saturated zone and exhibit evidence of groundwater fluctuations. The discovery of these groundwater discharge sites on a planet‐wide scale strongly suggests a link between the putative Martian ocean and various configurations of sedimentary deposits that were formed as a result of groundwater fluctuations during the Hesperian period. This newly recognised evidence of water formed features significantly increases the chance that biosignatures could be buried in the sediment. These deep basins (groundwater fed lakes) will be of interest to future exploration missions as they might provide evidence of geological conditions suitable for life. |
Febrero de 2019 Machine learning regression can predict macroscopic fault properties such as shear stress, friction, and time to failure using continuous records of fault zone acoustic emissions. Here we show that a similar |
approach is successful using event catalogs derived from the continuous data. Our methods are applicable to catalogs of arbitrary scale and magnitude of completeness. We investigate how machine learning regression from an event catalog of laboratory earthquakes performs as a function of the catalog magnitude of completeness. We find that strong model performance requires a sufficiently low magnitude of completeness, and below this magnitude of completeness, model performance saturates. |
Febrero de 2019 In recent years, the dwarf planet Ceres has been found to release water vapour. Detailed investigation of the surface and subsurface by NASA's Dawn mission reveal localized patches of |
surface ice and an ice abundance of around 10 % in the shallow subsurface, within a meter below the surface. Landis et al. 2018 quantify the expected sublimation from the surface and subsurface ice reservoirs at Ceres and the expected evaporation rates are factors of several lower than the observed ones. Although consideration of additional processes may possibly reduce the discrepancy, the origin of Ceres' exosphere is not yet clear. |
Febrero de 2019 The bathymetry and free‐air gravity data offshore Sunda trench are used here to analyze the flexural forebulge and bending moment variations along the Southeast Asian subduction zone. The observed bathymetry is corrected for various effects such as the sediment loading, lithosphere age, and the gravity derived isostatically compensated topography, which gave rise to the flexural deformation surface of the subducting Indo-Australian plate. From this, 28 across-trench sections were constructed to model the plate flexural bending along the Sunda trench. We observed that except in the northern |
Sumatra trench, rest of the Sunda trench is in agreement with the flexural model explained by the bending moment applied by the slab. In the northern Sumatra part of the trench, additional horizontal stresses of ~30–40 MPa are required for better match of the flexural forebulge thereby increasing the coupling with the upper plate. The outcome of this analysis in comparison with the slab depth variation, which abruptly reduces from ~600 km in Java to ~200 km toward northern Sumatra, suggests that very large bending moment and horizontal stresses are anticorrelated with the slab depth. The shorter slab in Sumatra does not effectively pull the incoming plate in the mantle, and therefore, plate convergence is accommodated at shallow depth, increasing the coupling with the upper plate. We propose that horizontal stresses are the result of the lateral propagation of the stronger slab pull from the neighboring deeper southeastern Java slab. |
Enero de 2019 The availability of GPS survey data spanning 22 years, along with several independent velocity solutions including up to 16 years of permanent GPS data, presents a unique opportunity to search for persistent (and thus reliable) deformation patterns in the Western Alps, which in turn allow a reinterpretation of the active tectonics of this region. While GPS velocities are still too uncertain to be interpreted on an individual basis, the analysis of range perpendicular GPS velocity profiles clearly highlights zones of extension in the center of the |
belt (15.3 to 3.1 nanostrain/year from north to south), with shortening in the forelands. The contrasting geodetic deformation pattern is coherent with earthquake focal mechanisms and related strain/stress patterns over the entire Western Alps. The GPS results finally provide a reliable and robust quantification of the regional strain rates. The observed vertical motions of 2.0 to 0.5 mm/year of uplift from north to south in the core of the Western Alps is interpreted to result from buoyancy forces related to postglacial rebound, erosional unloading, and/or viscosity anomalies in the crustal and lithospheric root. Spatial decorrelation between vertical and horizontal (seismicity related) deformation calls for a combination of processes to explain the complex present day dynamics of the Western Alps. |
Enero de 2019 It is now widely recognized that climate change affects multiple sectors in virtually every part of the world. Impacts on one sector may influence other sectors, including seemingly remote ones, which we call “interconnections of climate risks.” While a substantial number of climate risks are identified in the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5), there have been few attempts to explore the interconnections between them in a |
comprehensive way. To fill this gap, we developed a methodology for visualizing climate risks and their interconnections based on a literature survey. Our visualizations highlight the need to address climate risk interconnections in impact and vulnerability studies. Our risk maps and flowcharts show how changes in climate impact natural and socio-economic systems, ultimately affecting human security, health, and well-being. We tested our visualization approach with potential users and identified likely benefits and issues. Our methodology can be used as a communication tool to inform decision makers, stakeholders, and the general public of the cascading risks that can be triggered by climate change. |
Diciembre de 2018 Unusually high compressional (P) to shear (S) wave velocity ratios (Vp/Vs) were measured at different subduction zones and interpreted as fluid‐pressurized regions. Because no laboratory data reported such high values in isotropic rocks, mineralogical or anisotropic constrains were assumed. However, fluid-saturated rocks Vp/Vs |
is a frequency-dependent property so that standard laboratory measurements cannot be directly upscaled to the field. Using a new methodology, we measured the property in the elastic regime relevant to field measurements for diverse lithologies. We obtained extreme Vp/Vs values, consistent with those reported at seismic frequency in the field. Consistently with a model, it shows that if high fluid pressure is a key factor, anomalous Vp/Vs values could evidence intense degrees of microfracturation in isotropic rocks, whichever its mineralogical content. The permeability of these regions could be larger than 10−16 m2. |
Diciembre de 2018 The mechanical coupling between solid planets and their atmospheres enables seismically induced acoustic waves to propagate in the atmosphere. We numerically simulate this coupled system for two application cases: active seismic experiments (ASEs) and passive seismic experiments. A recent ASE (Krishnamoorthy et al., 2018, https://doi.org/10.1002/2018GL077481) observed |
the infrasonic signals produced by a seismic hammer. To measure the sensitivity of observations to seismic parameters, we attempt to reproduce the results from this experiment at short range by considering a realistic unconsolidated subsurface and an idealized rock-solid subsurface. At long range, we investigate the influence of the source by using two focal mechanisms. We found surface waves generate an infrasonic plane head wave in the ASE case of the rock-solid material. For the passive seismic experiments, the amplitude of atmospheric infrasound generated by seismic surface waves is investigated in detail. Despite some limitations, the simulations suggest that balloon measurement of seismically induced infrasound might help to constrain ground properties. |
Diciembre de 2018 Matched-filters are an increasingly popular tool for earthquake detection, but their reliance on a priori knowledge of the targets of interest limits their application to regions with previously documented seismicity. We explore an extension to the matched filter method to detect earthquakes and low frequency earthquakes on |
local to regional scales. We show that it is possible to increase the number of detections compared with standard energy based methods, with low false‐detection rates, using suites of synthetic waveforms as templates. We apply this to a microearthquake swarm and an aftershock sequence, and to detect low frequency earthquakes. We also explore the sensitivity of detections to the synthetic source's location and focal mechanism. Source‐receiver geometry has a first order control on how sensitive matched filter detectors are to variations in source location and focal mechanism, and this likely applies to detections made using both synthetic and real templates. |
Noviembre de 2018 Unusually high compressional (P) to shear (S) wave velocity ratios (Vp/Vs) were measured at different subduction zones, and interpreted as fluid-pressurized regions. Because no laboratory data reported such high values in isotropic rocks, mineralogical or anisotropic constrains were |
assumed. However, fluid saturated rocks’ Vp/Vs is a frequency dependent property so that standard laboratory measurements cannot be directly upscaled to the field. Using a new methodology, we measured the property in the elastic regime relevant to field measurements for diverse lithologies. We obtained extreme Vp/Vs values, consistent with those reported at seismic frequency in the field. Consistently with a model, it shows that if high fluid pressure is a key factor, anomalous Vp/Vs values could evidence intense degrees of micro-fracturation in isotropic rocks, whichever its mineralogical content. The permeability of these regions could be larger than 10-16 m2. |
Noviembre de 2018 Fracture damage patterns around faults induced by dynamic earthquake rupture are an invaluable record to clarify the rupture process on complex fault networks. The 2016 Mw 7.8 Kaikōura earthquake in New Zealand has been reported as one of the most complex earthquakes ever documented that ruptured at least 15 crustal |
faults. High-resolution optical satellite image displacement maps provide distinctive profiles of displacement across the faults and help visualize the off‐fault damage pattern. They are combined with field observation and coupled with a numerical tool that captures the dynamics of the rupture and simultaneous activation of off fault damage to allow the determination of the most likely rupture scenario. This study demonstrates that complex rupture processes can be explained in a rather simple way via a synergetic combination of state of the art observation and first principle physics based numerical modeling of off fault damage. |
Octubre de 2018 This study examined the FORMOSAT-3/COSMIC radio occultation soundings of total electron content in the ionosphere (from 150 to 550 km) and refractivity index in the lower atmosphere (from 0 to 60 km) after/during the 2011 Mw9.0 Tohoku earthquake/tsunami. The refractivity index observations show the first evidence of the |
Tohoku earthquake/tsunami-induced vertical oscillations in the lower atmosphere. The atmospheric oscillations with vertical wavelength ranging from 0.5 to 8 km and from 10 to 40 km, respectively, appear in the stratosphere and ionosphere after the earthquake onset. The short vertical wavelengths suggest that the oscillations are the atmospheric oscillatory tail due to the wavefront of the earthquake/tsunami. The radio occultation technique is a tool for detecting the atmospheric waves induced by earthquake or some other sources. |
Septiembre de 2018 The interplate zone beneath Mejillones Peninsula (MP) northern Chile, presents an anomalous seismogenic behavior with aseismic pulses, low coupling values and acting as a seismic barrier for earthquakes occurred in adjacent areas. We believe that this anomalous behavior is due to the presence of fluids in the interplate zone under the MP. To corroborate this, we study the seismicity recorded by a local seismological network and |
constructed a tomographic velocity model. Our results show that within the oceanic crust and in the lower continental crust exist the presence of fluids that concentrates to the north and center of the MP, which correlate with the presence of the Mejillones fracture zone and with more fractured and permeable lithologies of the continental crust. This situation changes to the south of the MP where fluid concentration is lower. This is the first detailed attempt to characterize the role of fluids in the rheology of barriers within subduction zones and to distinguish geological controls on the fluid distribution. We believe that this type of study is fundamental for facilitating future prospective analysis of earthquake distributions and conducting hazard assessments. |
Septiembre de 2018 To numerically simulate earthquake‐induced ionospheric disturbances, we extend the Wave Perturbation Global Ionosphere Thermosphere Model (WP GITM), which was originally developed for tsunami‐ionosphere coupling via gravity waves, to the case of earthquake‐ionosphere coupling via acoustic‐gravity waves. The new WP‐GITM represents epicentral crustal movements by a point source specified with the ground motion data from seismic |
measurements. The model then solves for the neutral atmospheric perturbations generated by spherical acoustic gravity waves and the resulting ionospheric plasma perturbations over the epicentral area. We apply the model to simulate the near‐field ionospheric disturbances during two major earthquake events: the 2011 Tohoku‐Oki, Japan and the 2015 Illapel, Chile events. To validate the results, we extract receiver to satellite total electron content (TEC) perturbations from the simulations and compare them to the corresponding slant TEC perturbations from Global Positioning System observations. We find good agreement on magnitudes and arrival times between the simulations and observations. |
Septiembre de 2018 Field portable instrumentation, such as in situ geochemical analyzers or broader field of view instruments like multispectral imagers or other imaging capabilities, has the potential to dramatically increase the science return of a planetary surface exploration mission. However, more work is needed to determine how emerging portable technologies should be designed and implemented into evolving mission architectures. This work summarizes the efforts of the RIS4E (Remote, In Situ and Synchrotron Studies for |
Science and Exploration) SSERVI (Solar System Exploration Research Virtual Institute) team in investigating how field portable instruments should be including into planning for future exploration EVAs (extravehicular activities). EVA crews of geologists and astronauts tested a variety of portable and handheld technologies at both the December 1974 lava flow, Kilauea Volcano, Hawai'i, and Kilbourne Hole, New Mexico, both of which are planetary analog sites. The timeline data gathered during instrument deployment were then mapped onto EVA timelines used in large‐scale NASA planetary surface exploration analog missions. Results and recommendations for future instrument hardware and software development are discussed, as is the operational framework necessary for incorporating in situ analytical capabilities into future planetary surface exploration. |
Septiembre de 2018 Los autores entrenaron una red neuronal artificial para estudiar las relaciones espaciales entre más de 130,000 terremotos principales y sus réplicas. En las pruebas, la IA fobtuvo mejores resultados en las ubicaciones de las réplicas respecto de los métodos tradicionales usados por la gran mayoría de los Sismólogos. El Abstract del paper afirma que: |
September 2018 Aftershocks are a response to changes in stress generated by large
earthquakes and represent the most common observations of the
triggering of earthquakes. The maximum magnitude of aftershocks
and their temporal decay are well described by empirical laws (such
as Bath’s law and Omori’s law), but explaining and forecasting the
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Agosto de 2018 A seismic moment tensor is a 3 × 3 symmetric matrix that provides a compact representation of a seismic source. We develop an algorithm to estimate moment tensors and their uncertainties from observed seismic data. For a given event, the algorithm performs a grid search over the six‐dimensional space of moment tensors by generating synthetic waveforms for each moment tensor and then evaluating a misfit function between the observed and synthetic waveforms. “The” moment tensor M0 for the event is then the moment tensor with minimum misfit. To describe the uncertainty associated with M0, we first |
convert the misfit function to a probability function. The uncertainty, or rather the confidence, is then given by the “confidence curve” urn:x-wiley:jgrb:media:jgrb52775:jgrb52775-math-0001, where urn:x-wiley:jgrb:media:jgrb52775:jgrb52775-math-0002 is the probability that the true moment tensor for the event lies within a certain neighborhood of M that has fractional volume V. The area under the confidence curve provides a single, abbreviated “confidence parameter” for M0. We apply the method to data from events in different regions and tectonic settings: 17 nuclear explosions and 12 earthquakes at the Nevada Test Site, 63 small (Mw<2.5) events at Uturuncu volcano in Bolivia, and 21 moderate (Mw>4) earthquakes in the southern Alaska subduction zone. Characterization of moment tensor uncertainties puts us in better position to discriminate among moment tensor source types and to assign physical processes to the events. |
Agosto de 2018 Determining earthquake hypocenters and focal mechanisms requires precisely measured P wave arrival times and first motion polarities. Automated algorithms for estimating these quantities have been less accurate than estimates by human experts, which are problematic for processing large data volumes. Here we train convolutional neural networks to measure both quantities, which learn directly from |
seismograms without the need for feature extraction. The networks are trained on 18.2 million manually picked seismograms for the Southern California region. Through cross validation on 1.2 million independent seismograms, the differences between the automated and manual picks have a standard deviation of 0.023 s. The polarities determined by the classifier have a precision of 95% when compared with analyst determined polarities. We show that the classifier picks more polarities overall than the analysts, without sacrificing quality, resulting in almost double the number of focal mechanisms. The remarkable precision of the trained networks indicates that they can perform as well, or better, than expert seismologists. |
Julio de 2018 Subduction megathrusts develop the largest earthquakes, often close to large population centers. Understanding the dynamics of deformation at subduction zones is therefore important to better assess seismic hazards. Here I develop consistent earthquake cycle simulations that incorporate localized and distributed deformation based on laboratory‐derived constitutive laws by combining boundary and volume elements to represent the mechanical coupling between megathrust slip and solid-state |
flow in the oceanic asthenosphere and in the mantle wedge. The model is simplified, in two dimensions, but may help the interpretation of geodetic data. Megathrust earthquakes and slow‐slip events modulate the strain rate in the upper mantle, leading to large variations of effective viscosity in space and time and a complex pattern of surface deformation. While fault slip and flow in the mantle wedge generate surface displacements in the same, that is, seaward, direction, the viscoelastic relaxation in the oceanic asthenosphere generates transient surface deformation in the opposite, that is, landward, direction above the rupture area of the mainshock. Aseismic deformation above the seismogenic zone may be challenging to record, but it may reveal important constraints about the rheology of the subducting plate. |
Junio de 2018 Between 2010 and 2015 three giant earthquakes occurred in the Chilean subduction where the oceanic Nazca plate plunges under South America. These were the largest events there since the gigantic M9.5 1960 earthquake so their close occurrences raise the question of a possible link between them. We show here that two-and-a-half days after the M8.2 Iquique |
earthquake, seismic activity started to increase downdip below (depth~100 km) the future Illapel epicenter. This increase, which began with the largest intermediate-depth earthquake in the Chilean subduction after Iquique, lasted until the M8.3 Illapel earthquake, 18 months later. The mechanisms involved suggest that the Iquique earthquake started a tear in the slab directly downdip from the future epicenter. This study relies on seismicity which occurs in the cold core of the slab and which is the only direct information we have on processes occurring at these depths. The results support that giant earthquakes interact at the scale of a subducting plate and suggest that this interaction occurs through the deep slab. |
Junio de 2018 Subduction megathrusts develop the largest earthquakes, often close to large population centers. Understanding the dynamics of deformation at subduction zones is therefore important to better assess seismic hazards. Here I develop consistent earthquake cycle simulations that incorporate localized and distributed deformation based on laboratory-derived constitutive laws by combining boundary and volume elements to represent the mechanical coupling between megathrust slip and solid-state |
flow in the oceanic asthenosphere and in the mantle wedge. The model is simplified, in two dimensions, but may help the interpretation of geodetic data. Megathrust earthquakes and slow-slip events modulate the strain rate in the upper mantle, leading to large variations of effective viscosity in space and time and a complex pattern of surface deformation. While fault slip and flow in the mantle wedge generate surface displacements in the same, that is, seaward, direction, the viscoelastic relaxation in the oceanic asthenosphere generates transient surface deformation in the opposite, that is, landward, direction above the rupture area of the mainshock. Aseismic deformation above the seismogenic zone may be challenging to record, but it may reveal important constraints about the rheology of the subducting plate. |
Junio de 2018 Paleoearthquakes and historic earthquakes are the most important source of information for the estimation of long-term earthquake recurrence intervals in fault zones, because corresponding sequences cover more than one seismic cycle. However, these events are often rare, dating uncertainties are enormous, and missing or misinterpreted events lead to additional problems. In the present study, I assume that the time to the next major earthquake depends on the rate of small and intermediate events between the large ones in terms of a “clock change” model. Mathematically, this leads to a Brownian passage time distribution for recurrence intervals. |
I take advantage of an earlier finding that under certain assumptions the aperiodicity of this distribution can be related to the Gutenberg- Richter b value, which can be estimated easily from instrumental seismicity in the region under consideration. In this way, both parameters of the Brownian passage time distribution can be attributed with accessible seismological quantities. This allows to reduce the uncertainties in the estimation of the mean recurrence interval, especially for short paleoearthquake sequences and high dating errors. Using a Bayesian framework for parameter estimation results in a statistical model for earthquake recurrence intervals that assimilates in a simple way paleoearthquake sequences and instrumental data. I present illustrative case studies from Southern California and compare the method with the commonly used approach of exponentially distributed recurrence times based on a stationary Poisson process. |
Junio de 2018 Between 2010 and 2015 three giant earthquakes occurred in the Chilean subduction where the oceanic Nazca plate plunges under South America. These were the largest events there since the gigantic M9.5 1960 earthquake so their close occurrences raise the question of a possible link between them. We show here that two-and-a-half days after the M8.2 Iquique |
earthquake, seismic activity started to increase downdip below (depth~100 km) the future Illapel epicenter. This increase, which began with the largest intermediate-depth earthquake in the Chilean subduction after Iquique, lasted until the M8.3 Illapel earthquake, 18 months later. The mechanisms involved suggest that the Iquique earthquake started a tear in the slab directly downdip from the future epicenter. This study relies on seismicity which occurs in the cold core of the slab and which is the only direct information we have on processes occurring at these depths. The results support that giant earthquakes interact at the scale of a subducting plate and suggest that this interaction occurs through the deep slab. |
Junio de 2018 The moment magnitude (Mw) 5.4 Pohang earthquake, the most damaging event in South Korea since instrumental seismic observation |
began in 1905, occurred beneath the Pohang geothermal power plant in 2017. Geological and geophysical data suggest that the Pohang earthquake was induced by fluid from an enhanced geothermal system (EGS) site, which was injected directly into a near-critically stressed subsurface fault zone. The magnitude of the mainshock makes it the largest known induced earthquake at an EGS site. |
Onemi - 5 claves para entender el monitoreo de los volcanes
Junio de 2018 Using ionospheric total electron contents residual data from 146 Global Navigation Satellite System stations in South America, we conducted three dimensional tomography of ionospheric electron density anomalies immediately before the 2015 Illapel Mw8.3 earthquake, Central Chile. We used |
five GPS and five GLONASS satellites and applied continuity constraints to regularize the linear least squares inversion. The reconstructed anomalies are composed of positive and negative regions, at altitudes of ~200 km and ~400 km, respectively, distributed roughly along the geomagnetic field. This feature suggests that the observed anomalies occurred by the downward E × B drift of electrons due to electric fields within ionosphere, possibly caused by surface positive electric charges. We also discuss the existence of the mirror image anomalies near the geomagnetic conjugate point of the epicenter using stations in Colombia. |
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Junio de 2018 On 16 September 2015, the Mw 8.4 Illapel earthquake occurred in central Chile with no intense foreshock sequences documented in the regional earthquake catalog. Here we employ the matched‐filter technique based on an enhanced template data set of previously catalogued events. We perform a continuous search over an ~4-year period before the Illapel mainshock to recover the uncatalogued small events and repeating earthquakes. Repeating earthquakes are found both to the north and south of the mainshock rupture zone. To the south of the rupture zone, the seismicity and repeater‐inferred aseismic slip |
progressively accelerate around the Illapel epicenter starting from ~140 days before the mainshock. This may indicate an unlocking process involving the interplay of seismic and aseismic slip. The acceleration culminates in a M 5.3 event of low angle thrust mechanism, which occurred ~36 days before the Mw 8.4 mainshock. It is then followed by a relative quiescence in seismicity until the mainshock occurred. This quiescence might correspond to an intermediate period of stable slip before rupture initiation. In addition, to the north of the mainshock rupture area, the last aseismic slip episode occurs within ~175–95 days before the mainshock and accumulates the largest amount of slip in the observation period. The simultaneous occurrence of aseismic slip transients over a large area is consistent with large scale slow unlocking processes preceding the Illapel mainshock. | |||
Junio de 2018 Seismogenic models have been recently proposed to explain precursors before earthquakes occurrences. Those models refer to physical processes linking the lithosphere, the atmosphere, and the ionosphere. We analyze in this work the curl-free current model describing the current flow from the lithosphere to the |
ionosphere through the atmosphere. We use a numerical simulation based on the finite element method to derive the current between the ground and the ionosphere. We have shown that the curl-free approximation of the atmospheric current density leads to significant and unpredictable distortions of the solutions of the electrical conductivity. Hence, it incorrectly expands the ionospheric disturbed region associated to lithospheric currents. It is shown that horizontally homogeneous vertical underground external currents cannot create currents from ground to the atmosphere. | |||
Junio de 2018 The mainshock aftershock sequence is one of the fundamental characteristics of seismogenesis, yet the physical mechanism of aftershock generation remains poorly understood. The simple explanation that aftershocks are caused by the mainshock's redistribution of strain energy is not always applicable, especially for aftershocks within the mainshock slip area, |
where strain energy is released. Here we show that the genesis of aftershocks can be modeled using a frictionally heterogeneous fault system. We conducted quasi-dynamic numerical simulations of fault rupture cycles on a finite fault governed by a rate and state-dependent friction law. Aftershocks are observed around and within the mainshock rupture area when the frictional heterogeneity varies significantly along the fault. On the other hand, aftershocks are not produced when along‐fault variations in the frictional heterogeneity are small, which mimics the observed lack of aftershocks for repeating earthquakes. | |||
Mayo de 2018 The moment magnitude (Mw) 5.5 earthquake that struck South Korea in November 2017 was one of the largest and most damaging events in that country over the past century. Its proximity to an enhanced geothermal system site, where high-pressure hydraulic injection had been performed |
during the previous 2 years, raises the possibility that this earthquake was anthropogenic. We have combined seismological and geodetic analyses to characterize the mainshock and its largest aftershocks, constrain the geometry of this seismic sequence, and shed light on its causal factors. According to our analysis, it seems plausible that the occurrence of this earthquake was influenced by the aforementioned industrial activities. Finally, we found that the earthquake transferred static stress to larger nearby faults, potentially increasing the seismic hazard in the area. | |||
Mayo de 2018 Since 2009, the midwestern United States has seen a dramatic rise in earthquakes induced by human activities. Most of these events were caused by massive reinjection of wastewater produced during oil and gas extraction (1, 2). In February 2016, regulators in Oklahoma called for an injection rate reduction after several major |
events up to moment magnitude 5.8 (Mw 5.8) occurred. On the other side of the Atlantic, an unprecedented number of earthquakes has followed gas extraction from the Groningen field in the Netherlands (3). The Dutch government imposed production cuts after a Mw 3.6 event in August 2012 caused structural damage to houses. Intensive research of these two instances of induced seismicity points to contrasting mechanisms, but in both cases, the natural conditions prior to subsurface activities play a dominant part. | |||
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Mayo de 2018 The Martian surface is cold, dry, exposed to biologically harmful radiation and apparently barren today. Nevertheless, there is clear geological evidence for warmer, wetter intervals in the past that could have supported life at or near the surface. This evidence has motivated NASA and ESA to prioritize the search for any remains or traces of organisms from early Mars in forthcoming missions. Informed by (1) stratigraphic, mineralogical and geochemical data collected by previous and current missions, (2) Earth's fossil record, and (3) experimental |
studies of organic decay and preservation, we here consider whether, how, and where fossils and isotopic biosignatures could have been preserved in the depositional environments and mineralizing media thought to have been present in habitable settings on early Mars. We conclude that Noachian–Hesperian Fe-bearing clay-rich fluvio-lacustrine siliciclastic deposits, especially where enriched in silica, currently represent the most promising and best understood astropaleontological targets. Siliceous sinters would also be an excellent target, but their presence on Mars awaits confirmation. More work is needed to improve our understanding of fossil preservation in the context of other environments specific to Mars, particularly within evaporative salts and pore/fracture-filling subsurface minerals. | |||
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Mayo de 2018 Performance of earthquake early warning (EEW) systems suffers from false alerts caused by local impulsive noise from natural or anthropogenic sources. To mitigate this problem, we train a Generative Adversarial Network (GAN) to learn the characteristics of first-arrival earthquake P waves, using 300,000 waveforms recorded in southern |
California and Japan. We apply the GAN critic as an automatic feature extractor and train a Random Forest classifier with about 700,000 earthquake and noise waveforms. We show that the discriminator can recognize 99.2% of the earthquake P waves and 98.4% of the noise signals. This state-of-the-art performance is expected to reduce significantly the number of false triggers from local impulsive noise. Our study demonstrates that GANs can discover a compact and effective representation of seismic waves, which has the potential for wide applications in seismology. | |||
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Mayo de 2018 The two major explosive phases of the 22–23 April 2015 eruption of Calbuco volcano, Chile, produced powerful seismicity and infrasound. The eruption was recorded on seismo-acoustic stations out to 1,540 km and on five stations (IS02, IS08, IS09, IS27, and IS49) of the International Monitoring System (IMS) infrasound network at distances from 1,525 to 5,122 km. The remote IMS infrasound stations provide an |
accurate explosion chronology consistent with the regional and local seismo-acoustic data and with previous studies of lightning and plume observations. We use the IMS network to detect and locate the eruption signals using a brute-force, grid-search, cross-bearings approach. After incorporating azimuth deviation corrections from stratospheric crosswinds using 3-D ray tracing, the estimated source location is 172 km from true. This case study highlights the significant capability of the IMS infrasound network to provide automated detection, characterization, and timing estimates of global explosive volcanic activity. Augmenting the IMS with regional seismo-acoustic networks will dramatically enhance volcanic signal detection, reduce latency, and improve discrimination capability. | |||
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Mayo de 2018 The 2014 Iquique-Pisagua Mw 8.1 earthquake ruptured only parts of the 1877 Northern Chile-Southern Peru seismic gap. Here we present a comprehensive analysis of 152 continuous and campaign Global Positioning System time series that captured more than a decade of interseismic loading prior to the event and 2 years of afterslip. In high spatiotemporal resolution, our data document upper plate response not only at the coseismically affected latitudes but also at the adjacent Loa plate segment to the south. Using a combination of elastic and viscoelastic half-space models of different stages of the seismic cycle, |
we found that the highly coupled, former seismic gap contains a narrow low coupling zone at 21°S latitude. Just after the 2014 earthquake, this zone acts as a barrier impeding afterslip to continue southward. Possible reasons for this impediment could involve crustal heterogeneities or coupling discontinuities at the plate interface. After 2 years, afterslip cumulates to a maximum of ~89 cm and becomes negligible. Global Positioning System observations south of the inferred seismotectonic barrier reveal a deformation rate increase in the second year after the event. Our slip models suggest that this could be caused by a downdip coupling increase, perhaps bringing the highly coupled southern Loa segment closer to failure. Taken together, our results reveal (1) the interaction between different areas undergoing stress release and stress buildup in a major seismic gap, (2) constraints for the temporal variation of coupling degree in different stages of the seismic cycle, and (3) the influence of large earthquakes at adjacent segments. | |||
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Abril de 2018 As the costs and regulatory barriers
to new water supply development continue to rise, drought management
strategies have begun to |
development of financial index insurance designed to compensate a utility for drought related losses. The focus is on analyzing candidate hydrologic indices that have the potential to be used by utilities across the US, increasing the potential for risk pooling, which would offer the possibility of both lower risk management costs and more widespread implementation. This work first analyzes drought related financial risks for 315 publicly operated water utilities across the country and examines the effectiveness of financial contracts based on several indices both in terms of their correlation with utility revenues and their spatial autocorrelation across locations. Hydrologic based index insurance contracts are then developed and tested over a 120 year period. Results indicate that risk pooling, even under conditions in which droughts are subject to some level of spatial autocorrelation, has the potential to significantly reduce the cost of managing financial risk. | |||
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Abril de 2018 Geochemically discriminating between magmatism in different tectonic settings remains a fundamental part of understanding the processes of magma generation within the Earth's mantle. Here we present an approach where machine learning (ML) methods are used for quantitative tectonic discrimination and feature selection using global geochemical data sets containing data for volcanic rocks generated in eight different tectonic settings. This study uses support vector machine, random forest, and sparse multinomial regression (SMR) approaches. All these ML methods with data for 24 elements and five isotopic ratios allowed the successful geochemical discrimination between igneous rocks formed in eight different tectonic |
settings with a discriminant ratio better
than 83% for all settings barring oceanic plateaus and back-arc basins.
SMR is a particularly powerful and interpretable ML method because it
quantitatively identifies geochemical signatures that characterize the
tectonic settings of interest and the characteristics of each sample
as a probability of the membership of the sample for each setting. We
also present the most representative basalt composition for each tectonic
setting. The new data provide reference points for future geochemical
discussions. Our results indicate that at least 17 elements and isotopic
ratios are required to characterize each tectonic setting, suggesting
that geochemical tectonic discrimination cannot be achieved using only
a small number of elemental compositions and/or isotopic ratios. The
results show that volcanic rocks formed in different tectonic settings
have unique geochemical signatures, indicating that both volcanic rock
geochemistry and magma generation processes are closely connected to
the tectonic setting. |
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Abril de 2018 On 16 September 2015, the Mw 8.4 Illapel earthquake occurred in central Chile with no intense foreshock sequences documented in the regional earthquake catalog. Here we employ the matched-filter technique based on an enhanced template data set of previously catalogued events. We perform a continuous search over an ~4-year period before the Illapel mainshock to recover the uncatalogued small events and repeating earthquakes. Repeating earthquakes are found both to the north and south of the mainshock rupture zone. To the south of the rupture zone, the seismicity and repeater-inferred aseismic slip |
progressively accelerate around the Illapel epicenter starting from ~140 days before the mainshock. This may indicate an unlocking process involving the interplay of seismic and aseismic slip. The acceleration culminates in a M 5.3 event of low-angle thrust mechanism, which occurred ~36 days before the Mw 8.4 mainshock. It is then followed by a relative quiescence in seismicity until the mainshock occurred. This quiescence might correspond to an intermediate period of stable slip before rupture initiation. In addition, to the north of the mainshock rupture area, the last aseismic-slip episode occurs within ~175–95 days before the mainshock and accumulates the largest amount of slip in the observation period. The simultaneous occurrence of aseismic-slip transients over a large area is consistent with large-scale slow unlocking processes preceding the Illapel mainshock. | |||
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Abril de 2018 Using ionospheric total electron contents residual data from 146 Global Navigation Satellite System stations in South America, we conducted three-dimensional tomography of ionospheric electron density anomalies immediately before the 2015 Illapel Mw8.3 earthquake, Central Chile. We used five GPS and five GLONASS satellites and applied |
continuity constraints to regularize the linear least squares inversion. The reconstructed anomalies are composed of positive and negative regions, at altitudes of ~200 km and ~400 km, respectively, distributed roughly along the geomagnetic field. This feature suggests that the observed anomalies occurred by the downward E × B drift of electrons due to electric fields within ionosphere, possibly caused by surface positive electric charges. We also discuss the existence of the mirror image anomalies near the geomagnetic conjugate point of the epicenter using stations in Colombia. | |||
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Abril de 2018 Nosotros presentamos SubMachine,
una colección de herramientas web para la visualización
interactiva, análisis y comparación cuantitativa de
conjuntos de datos de escala mundial del interior de la Tierra. SubMachine
se enfoca en facilitar el acceso y la utilización de los modelos
de tomografía sísmica por parte de la comunidad que
estudia la Tierra Sólida, para así facilitar la exploración
colaborativa. Nosotros hemos escrito programas específicos
para visualizar y explorar sobre 30 modelos tomográficos -
individualmente, lado a lado o a través de estadísticas
y promedios. |
Abril de 2018 Link: SubMachine |
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Marzo de 2018 The two major explosive phases of the 22–23 April 2015 eruption of Calbuco volcano, Chile produced powerful seismicity and infrasound. The eruption was recorded on seismo‐acoustic stations out to 1,540 km and on 5 stations (IS02, IS08, IS09, IS27, and IS49) of the International Monitoring System (IMS) infrasound network at distances from 1,525 to 5,122 km. The remote IMS infrasound stations provide an accurate explosion chronology consistent with the regional |
and local seismo acoustic data, and with previous studies of lightning and plume observations. We use the IMS network to detect and locate the eruption signals using a brute force, grid search, cross bearings approach. After incorporating azimuth deviation corrections from stratospheric cross winds using 3D ray tracing, the estimated source location is 172 km from true. This case study highlights the significant capability of the IMS infrasound network to provide automated detection, characterization, and timing estimates of global explosive volcanic activity. Augmenting the IMS with regional seismo acoustic networks will dramatically enhance volcanic signal detection, reduce latency, and improve discrimination capability. | |||
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Marzo de 2018 The sharp rise in Oklahoma seismicity since 2009 is due to wastewater injection. The role of injection depth is an open, complex issue, yet critical for hazard assessment and regulation. We developed an advanced Bayesian network to model joint conditional dependencies between spatial, operational, and seismicity parameters. |
We found that injection depth relative to crystalline basement most strongly correlates with seismic moment release. The joint effects of depth and volume are critical, as injection rate becomes more influential near the basement interface. Restricting injection depths to 200 to 500 meters above basement could reduce annual seismic moment release by a factor of 1.4 to 2.8. Our approach enables identification of subregions where targeted regulation may mitigate effects of induced earthquakes, aiding operators and regulators in wastewater disposal regions. | |||
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Febrero de 2018 During the past few decades numerical
studies have been widely employed to explore the style of circulation
and mixing in the mantle of Earth and other planets. However, in geodynamical
studies there are many properties from mineral physics, geochemistry,
and petrology in these numerical models. Machine learning, as a computational
statistic-related technique and a subfield of artificial intelligence,
has rapidly emerged recently in many fields of sciences and engineering.
We focus here on the application of supervised machine learning (SML)
algorithms in predictions of mantle flow processes. Specifically,
we |
emphasize on estimating mantle properties by employing machine learning techniques in solving an inverse problem. Using snapshots of numerical convection models as training samples, we enable machine learning models to determine the magnitude of the spin transition-induced density anomalies that can cause flow stagnation at midmantle depths. Employing support vector machine algorithms, we show that SML techniques can successfully predict the magnitude of mantle density anomalies and can also be used in characterizing mantle flow patterns. The technique can be extended to more complex geodynamic problems in mantle dynamics by employing deep learning algorithms for putting constraints on properties such as viscosity, elastic parameters, and the nature of thermal and chemical anomalies. | |||
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Febrero de 2018 The 2015 Paris Agreement aims to
limit global warming to well below 2 K above preindustrial levels,
and to pursue efforts to limit global warming to 1.5 K, in order to
avert dangerous climate change. However, current greenhouse gas emissions
targets are more compatible with scenarios exhibiting end-of-century
global warming of 2.6–3.1 K, in clear contradiction to the 1.5 K
target. In this study, we use a global climate model to investigate
the climatic impacts of using solar geoengineering by stratospheric
aerosol injection to stabilize global-mean temperature at |
1.5 K for the duration of the 21st century against three scenarios spanning the range of plausible greenhouse gas mitigation pathways (RCP2.6, RCP4.5, and RCP8.5). In addition to stabilizing global mean temperature and offsetting both Arctic sea-ice loss and thermosteric sea-level rise, we find that solar geoengineering could effectively counteract enhancements to the frequency of extreme storms in the North Atlantic and heatwaves in Europe, but would be less effective at counteracting hydrological changes in the Amazon basin and North Atlantic storm track displacement. In summary, solar geoengineering may reduce global mean impacts but is an imperfect solution at the regional level, where the effects of climate change are experienced. Our results should galvanize research into the regionality of climate responses to solar geoengineering. | |||
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Febrero de 2018 Accelerating rates of quasiperiodic “drumbeat” long-period earthquakes (LPs) are commonly reported before eruptions at andesite and dacite volcanoes, and promise insights into the nature of fundamental preeruptive processes and improved eruption forecasts. Here we apply a new Bayesian Markov chain Monte Carlo gamma point process methodology to investigate an exceptionally well- |
developed sequence of drumbeat LPs preceding a recent large vulcanian explosion at Tungurahua volcano, Ecuador. For more than 24 hr, LP rates increased according to the inverse power law trend predicted by material failure theory, and with a retrospectively forecast failure time that agrees with the eruption onset within error. LPs resulted from repeated activation of a single characteristic source driven by accelerating loading, rather than a distributed failure process, showing that similar precursory trends can emerge from quite different underlying physics. Nevertheless, such sequences have clear potential for improving forecasts of eruptions at Tungurahua and analogous volcanoes. | |||
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Febrero de 2018 Fire regimes across the globe have great spatial and temporal variability, and these are influence by many factors including anthropogenic management, climate and vegetation types. Here we utilise the satellite based ‘active fire’ product, from MODIS sensors, to statistically analyse variability and trends in fire activity from the global to regional scales. We split up the regions by economic development, region/geographical land-use, clusters of fire-abundant areas or by religious/cultural influence. Weekly cycle tests are conducted to highlight and quantify part of the anthropogenic influence on fire regime across the |
world. We find that there is a strong statistically significant decline in 2001-2016 active fires globally linked to an increase in net primary productivity observed in northern Africa, along with global agricultural expansion and intensification, which generally reduces fire activity. There are high levels of variability however. The large-scale regions exhibit either little change or decreasing in fire activity except for strong increasing trends in India and China, where rapid population increase is occurring, leading to agricultural intensification and increased crop residue burning. Variability in Canada has been linked to a warming global climate leading to a longer growing season and higher fuel loads. Areas with a strong weekly cycle give a good indication of where fire management is being applied most extensively, e.g. the USA, where few areas retain a natural fire regime. | |||
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Febrero de 2018 Earthquakes can change the stress field in the Earth's lithosphere as they relieve and redistribute stress. Earthquake-induced stress changes have been observed as temporal rotations of the principal stress axes following major earthquakes in a variety of tectonic settings. The stress changes due to the 2011 Mw9.0 Tohoku-Oki, Japan, earthquake were particularly well documented. Earthquake stress rotations can inform our understanding of earthquake physics, most notably addressing the long-standing |
problem of whether the Earth's crust at plate boundaries is “strong” or “weak.” Many of the observed stress rotations, including that due to the Tohoku-Oki earthquake, indicate near-complete stress drop in the mainshock. This implies low background differential stress, on the order of earthquake stress drop, supporting the weak crust model. Earthquake stress rotations can also be used to address other important geophysical questions, such as the level of crustal stress heterogeneity and the mechanisms of postseismic stress reloading. The quantitative interpretation of stress rotations is evolving from those based on simple analytical methods to those based on more sophisticated numerical modeling that can capture the spatial-temporal complexity of the earthquake stress changes. | |||
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Enero de 2018 A sharp increase in the frequency of earthquakes near Fox Creek, Alberta, began in December 2013 in response to hydraulic fracturing. Using a hydraulic fracturing database, we explore relationships between injection parameters and seismicity response. We show that induced earthquakes are associated with completions that |
used larger injection volumes (104 to 105 cubic meters) and that seismic productivity scales linearly with injection volume. Injection pressure and rate have an insignificant association with seismic response. Further findings suggest that geological factors play a prominent role in seismic productivity, as evidenced by spatial correlations. Together, volume and geological factors account for ~96% of the variability in the induced earthquake rate near Fox Creek. This result is quantified by a seismogenic index–modified frequency-magnitude distribution, providing a framework to forecast induced seismicity. | |||
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Enero de 2018 This study aims at understanding the role of tidal level, speed, and direction in tsunami propagation in highly energetic tidal channels. The main goal is to comprehend whether tide-tsunami interactions enhance/reduce elevation, currents speeds, and arrival times, when compared to pure tsunami models and to simulations in which tides and tsunamis are linearly superimposed. We designed various numerical experiments to compute the tsunami propagation along Canal Chacao, a highly energetic channel in the Chilean Patagonia lying on a subduction margin prone to megathrust earthquakes. Three modeling approaches were implemented under the same |
seismic scenario: a tsunami model with a constant tide level, a series of six composite models in which independent tide and tsunami simulations are linearly superimposed, and a series of six tide-tsunami nonlinear interaction models (full models). We found that hydrodynamic patterns differ significantly among approaches, being the composite and full models sensitive to both the tidal phase at which the tsunami is triggered and the local depth of the channel. When compared to full models, composite models adequately predicted the maximum surface elevation, but largely overestimated currents. The amplitude and arrival time of the tsunami-leading wave computed with the full model was found to be strongly dependent on the direction of the tidal current and less responsive to the tide level and the tidal current speed. These outcomes emphasize the importance of addressing more carefully the interactions of tides and tsunamis on hazard assessment studies. | |||
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Enero de 2018 Geothermal heat flux (GHF) is a crucial boundary condition for making accurate predictions of ice sheet mass loss, yet it is poorly known in Greenland due to inaccessibility of the bedrock. Here we use a machine learning algorithm on a large collection of relevant geologic features and global GHF measurements and produce a GHF |
map of Greenland that we argue is within ~15% accuracy. The main features of our predicted GHF map include a large region with high GHF in central-north Greenland surrounding the NorthGRIP ice core site, and hot spots in the Jakobshavn Isbræ catchment, upstream of Petermann Gletscher, and near the terminus of Nioghalvfjerdsfjorden glacier. Our model also captures the trajectory of Greenland movement over the Icelandic plume by predicting a stripe of elevated GHF in central-east Greenland. Finally, we show that our model can produce substantially more accurate predictions if additional measurements of GHF in Greenland are provided. | |||
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Diciembre de 2017 In a context of global change and increasing anthropic pressure on the environment, monitoring the Earth system and its evolution has become one of the key missions of geosciences. Geodesy is the geoscience that measures the geometric shape of the Earth, its orientation in space, and gravity field. Time-variable gravity, because of its high accuracy, can be used to build an enhanced picture and understanding of the |
changing Earth. Ground-based gravimetry can determine the change in gravity related to the Earth rotation fluctuation, to celestial body and Earth attractions, to the mass in the direct vicinity of the instruments, and to vertical displacement of the instrument itself on the ground. In this paper, we review the geophysical questions that can be addressed by ground gravimeters used to monitor time-variable gravity. This is done in relation to the instrumental characteristics, noise sources, and good practices. We also discuss the next challenges to be met by ground gravimetry, the place that terrestrial gravimetry should hold in the Earth observation system, and perspectives and recommendations about the future of ground gravity instrumentation. | |||
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Diciembre de 2017 Fusing satellite observations and station measurements to estimate ground-level PM2.5 is promising for monitoring PM2.5 pollution. A geo-intelligent approach, which incorporates geographical correlation into an intelligent deep learning architecture, is developed to estimate PM2.5. Specifically, it considers geographical distance and spatiotemporally correlated PM2.5 in |
a deep belief network (denoted as Geoi-DBN). Geoi-DBN can capture the essential features associated with PM2.5 from latent factors. It was trained and tested with data from China in 2015. The results show that Geoi-DBN performs significantly better than the traditional neural network. The out-of-sample cross-validation R2 increases from 0.42 to 0.88, and RMSE decreases from 29.96 to 13.03 µg/m3. On the basis of the derived PM2.5 distribution, it is predicted that over 80% of the Chinese population live in areas with an annual mean PM2.5 of greater than 35 µg/m3. This study provides a new perspective for air pollution monitoring in large geographic regions. | |||
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Diciembre de 2017 In the first months of 2007, the Aysén region in southern Chile was affected by a crustal seismic swarm. Its largest earthquake (Mw 6.2) occurred in April, and had its epicenter in Aysén Fjord. Seismic intensities became so high that hundreds of onshore mass movements were triggered, several of which entered into the fjord, resulting in mass-transport deposits (MTDs) preserved at the fjord bottom. Here we present a Holocene record of paleo-earthquakes in the previously unstudied Patagonian fjordland based on MTD stratigraphy. High-resolution seismic data retrieved using two different seismic systems (sparker and TOPAS) reveal multiple |
older MTDs on different stratigraphic levels. Correlation of the seismic stratigraphy with sedimentological data obtained from a long Calypso core (MD07-3117) allows conclusion on the seismic origin of these deposits. Additionally, radiocarbon dating permits constructing an age model, validated by tephrochronology, providing an age for the different MTD levels. We thus present a highly detailed paleoseismological history of the Aysén region, including at least six major Holocene earthquakes, one of which is likely related to a known megathrust earthquake. Other earthquakes are related to activity of the Liquiñe-Ofqui Fault Zone (LOFZ), forming the main source of seismic hazard in the area. We can infer a general average recurrence time for LOFZ earthquakes of ~2,100 years in the vicinity of Aysén Fjord with clustered events during the Early and Late Holocene. Finally, we argue that cascading events (causal link between volcanic and seismic events) may be a frequent phenomenon along the LOFZ. | |||
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Diciembre de 2017 We develop a methodology that combines compressive sensing back-projection (CS-BP) and source spectral analysis of teleseismic P waves to provide metrics relevant to earthquake dynamics of large events. We improve the CS-BP method by an auto-adaptive source grid refinement as well as a reference source adjustment technique to gain better spatial and temporal resolution of the locations of the radiated bursts. We also use a two-step source spectral analysis based on i) simple theoretical Green's functions that include depth phases and water reverberations and on ii) empirical P-wave Green's functions. Furthermore, we propose a source spectrogram methodology that provides |
the temporal evolution of dynamic parameters such as radiated energy and falloff rates. Bridging back-projection and spectrogram analysis provides a spatial and temporal evolution of these dynamic source parameters. We apply our technique to the recent 2015 Mw 8.3 megathrust Illapel earthquake (Chile). The results from both techniques are consistent and reveal a depth-varying seismic radiation that is also found in other megathrust earthquakes. The low frequency content of the seismic radiation is located in the shallow part of the megathrust, propagating unilaterally from the hypocenter towards the trench while most of the high frequency content comes from the downdip part of the fault. Interpretation of multiple rupture stages in the radiation is also supported by the temporal variations of radiated energy and falloff rates. Finally, we discuss the possible mechanisms, either from pre-stress, fault geometry, and/or frictional properties to explain our observables. Our methodology is an attempt to bridge kinematic observations with earthquake dynamics. |
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Diciembre de 2017 We present a four-category classification
algorithm for the solar wind, based on Gaussian Process. The four
categories are the ones previously adopted in Xu and Borovsky (2015):
ejecta, coronal hole origin plasma, streamer belt origin plasma, and
sector reversal origin plasma. The algorithm is trained and tested
on a labeled portion of the OMNI data set. It uses seven inputs: the
solar wind speed Vsw, the temperature standard deviation sT, the sunspot
number R, the F10.7 index, the Alfven speed vA, the proton specific
entropy Sp, and the proton temperature Tp compared to a velocity-dependent
expected |
temperature. The output of the Gaussian Process classifier is a four-element vector containing the probabilities that an event (one reading from the hourly averaged OMNI database) belongs to each category. The probabilistic nature of the prediction allows for a more informative and flexible interpretation of the results, for instance, being able to classify events as “undecided.” The new method has a median accuracy larger than 90% for all categories, even using a small set of data for training. The Receiver Operating Characteristic curve and the reliability diagram also demonstrate the excellent quality of this new method. Finally, we use the algorithm to classify a large portion of the OMNI data set, and we present for the first time transition probabilities between different solar wind categories. Such probabilities represent the “climatological” statistics that determine the solar wind baseline. | |||
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Diciembre de 2017 We present the PINE (Plasma density in the Inner magnetosphere Neural network-based Empirical) model - a new empirical model for reconstructing the global dynamics of the cold plasma density distribution based only on solar wind data and geomagnetic indices. Utilizing the density database obtained using the NURD (Neural-network-based Upper hybrid Resonance Determination) algorithm for the period of 1 October 2012 to 1 July 2016, in conjunction with solar wind data and geomagnetic indices, we develop a neural network model that is capable of globally reconstructing the dynamics of the cold plasma density distribution for 2=L=6 and all local times. We validate and test the model by |
measuring its performance on independent data sets withheld from the training set and by comparing the model-predicted global evolution with global images of He+ distribution in the Earth's plasmasphere from the IMAGE Extreme UltraViolet (EUV) instrument. We identify the parameters that best quantify the plasmasphere dynamics by training and comparing multiple neural networks with different combinations of input parameters (geomagnetic indices, solar wind data, and different durations of their time history). The optimal model is based on the 96?h time history of Kp, AE, SYM-H, and F10.7 indices. The model successfully reproduces erosion of the plasmasphere on the nightside and plume formation and evolution. We demonstrate results of both local and global plasma density reconstruction. This study illustrates how global dynamics can be reconstructed from local in situ observations by using machine learning techniques. | |||
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Diciembre de 2017 Ocean basins record the life history of a tectonic plate—its creation at a mid-ocean ridge, its thickening over time, and its consumption at a subduction zone. The movement of tectonic plates is possible because the lithosphere, Earth's stiff outermost shell, slides on top of a weak asthenosphere. Despite its fundamental role in facilitating plate tectonics, the nature of the |
lithosphere-asthenosphere boundary is poorly understood. The asthenosphere is on average warmer than the lithosphere, but the temperature contrast alone may not provide the necessary viscosity reduction. Previous work has also proposed a dehydrated lithosphere and damp asthenosphere (1), and a solid lithosphere and partially molten asthenosphere (2). On page 1593 of this issue, Takeuchi et al. (3) present an analysis of aftershocks of the 2011 Tohoku earthquake and show how the attenuation of seismic waves has a different frequency response in the lithosphere versus the asthenosphere. | |||
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Noviembre de 2017 In a context of global change and increasing anthropic pressure on the environment, monitoring the Earth system and its evolution has become one of the key missions of geosciences. Geodesy is the geoscience that measures the geometric shape of the Earth, its orientation in space, and gravity field. Time-variable gravity, because of its high accuracy, can be used to build an enhanced picture and understanding of the changing Earth. Ground-based gravimetry can |
determine the change in gravity related to the Earth rotation fluctuation, to celestial body and Earth attractions, to the mass in the direct vicinity of the instruments, and to vertical displacement of the instrument itself on the ground. In this paper, we review the geophysical questions that can be addressed by ground gravimeters used to monitor time-variable gravity. This is done in relation to the instrumental characteristics, noise sources, and good practices. We also discuss the next challenges to be met by ground gravimetry, the place that terrestrial gravimetry should hold in the Earth observation system, and perspectives and recommendations about the future of ground gravity instrumentation. | |||
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Noviembre de 2017 Since 1990, nearly one million people
have died from the impacts of earthquakes. Reducing those impacts
requires building a local seismic culture in which residents are aware
of earthquake risks and value efforts to mitigate harm. Such efforts |
include earthquake early warning (EEW) systems that provide seconds to minutes notice of pending shaking. Recent events in Mexico provide an opportunity to assess performance and perception of an EEW system and highlight areas for further improvement. We have learned that EEW systems, even imperfect ones, can help people prepare for earthquakes and build local seismic culture, both beneficial in reducing earthquake-related losses. | |||
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Noviembre de 2017 After an earthquake, the earliest
deformation signals are not expected to be carried by the fastest
(P) elastic waves but by the speed-of-light changes of the gravitational
field. However, these perturbations are weak and, so far, their detection
has not been accurate enough to fully understand |
their origins and to use them for a highly valuable rapid estimate of the earthquake magnitude. We show that gravity perturbations are particularly well observed with broadband seismometers at distances between 1000 and 2000 kilometers from the source of the 2011, moment magnitude 9.1, Tohoku earthquake. We can accurately model them by a new formalism, taking into account both the gravity changes and the gravity-induced motion. These prompt elastogravity signals open the window for minute time-scale magnitude determination for great earthquakes. | |||
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Noviembre de 2017 Comparison of pre-event geodetic
and geologic rates in three large-magnitude (Mw=7.6-7.9) strike-slip
earthquakes reveals a wide range of behaviors. Specifically, geodetic
rates of 26-28 mm/yr for the North Anatolian fault along the 1999
MW=7.6 Izmit rupture are ∼40% faster than Holocene geologic rates.
In contrast, geodetic rates of 6-8 mm/yr along the Denali fault prior
to the 2002 MW=7.9 Denali earthquake are only half as fast as the
latest Pleistocene-Holocene geologic rate of 12 mm/yr. In the third
example where a sufficiently long pre-earthquake geodetic |
time series exists, the geodetic and geologic rates along the 2001 MW=7.8 Kokoxili rupture on the Kunlun fault are approximately equal at 11 mm/yr. These results are not readily explicable with extant earthquake cycle modeling, suggesting that they may instead be due to some combination of regional kinematic fault interactions, temporal variations in the strength of lithospheric-scale shear zones, and/or variations in local relative plate motion rate. Whatever the exact causes of these variable behaviors, these observations indicate that either the ratio of geodetic to geologic rates before an earthquake may not be diagnostic of the time to the next earthquake, as predicted by many rheologically based geodynamic models of earthquake cycle behavior, or that different behaviors characterize different fault systems in a manner that is not yet understood or predictable. | |||
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Noviembre de 2017 This paper presents a single-layer
travelling-wave antenna (TWA) that is based on composite right/left-handed
(CRLH)-metamaterial (MTM) transmission-line (TL) structure, which
is implemented by using a combination of inter-digital capacitors
and dual-spiral inductive slots. By embedding dual-spiral inductive
slots inside |
the CRLH MTM-TL results in a compact TWA. Dimensions of the proposed CRLH MTM-TL TWA is 21.5×30.0 mm2 or 0.372λ0×0.520λ0 at 5.2 GHz (center frequency). The fabricated TWA operates over 1.8–8.6 GHz with a fractional bandwidth greater than 120%, and it exhibits a peak gain and radiation efficiency of 4.2 dBi and 81%, respectively, at 5 GHz. By avoiding the use of lumped components, via-holes or defected ground structures (DGS), the proposed TWA design is economic for mass production as well as easy to integrate with wireless communication systems. | |||
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Noviembre de 2017 The Valparaiso 2017 sequence occurred
in the Central Chile megathrust, an active zone where the last mega-earthquake
occurred in 1730. Intense seismicity started 2 days before the Mw
6.9 mainshock, a slow trenchward movement was observed in the coastal
GPS antennas and was accompanied by foreshocks and repeater- |
type seismicity. To characterize the rupture process of the mainshock, we perform a dynamic inversion using the strong-motion records and an elliptical patch approach. We suggest that a slow slip event preceded and triggered the Mw 6.9 earthquake, which ruptured an elliptical asperity (semiaxis of 10 km and 5 km, with a subshear rupture, stress drop of 11.71 MPa, yield stress of 17.21 MPa, slip weakening of 0.65 m, and kappa value of 1.98). This earthquake could be the beginning of a long-term nucleation phase to a major rupture, within the highly coupled Central Chile zone where a megathrust earthquake like 1730 is expected. | |||
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Noviembre de 2017 For decades, scientists have charted tiny fluctuations in the length of Earth's day: Gain a millisecond here, lose a millisecond there. Last week at the annual meeting of the Geological Society of America in Seattle, Washington, two geophysicists argued that these minute changes |
could be correlated with the timing of major earthquakes—and potentially help forecast them. During the past 100 years, Earth's slowdowns have matched surprisingly well with periods of global increases in the frequency of magnitude-7 and larger earthquakes. Each spike happens well after the slowdown, offering a 5-year heads up on future quakes. So far, researchers have only fuzzy ideas about how changes in Earth's molten iron core might cause this pattern, but they say the finding is too provocative to ignore. | |||
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Octubre de 2017 Durante la última decada se ha incrementado la atención en la investigación de la predicción de terremotos por medio de técnicas de Data Mining. Muchos trabajos han presentado diversos indicadores sísmicos como inputs para Clasificadores Supervisados. Sin embargo estos indicadores han sido utilizados sin una previa transformación. En este trabajo utilizamos Análisis de Componentes Principales (ACP) para reducir la dimensionalidad de los vectores input para así generar nuevos datsets y colocar este procedimiento como un paso intermedio en una exitosa metodología que hoy se utiliza para predecir terremotos. Nuestra investigación la aplicamos a Tokyo, una de las ciudades japonesas más amenazadas por grandes terremotos. Utilizamos diversosy muy bien conocidos Clasificadores junto con ACP y reportamos notorias mejoras en la predicción. |
Octubre de 2017 Increasing attention has been paid to the prediction of earthquakes with data mining techniques during the last decade. Several works have already proposed the use of certain features serving as inputs for supervised classifiers. However, they have been successfully used without any further transformation so far. In this work, the use of principal component analysis (PCA) to reduce data dimensionality and generate new datasets is proposed. In particular, this step is inserted in a successfully already used methodology to predict earthquakes. Tokyo, one of the cities mostly threatened by large earthquakes occurrence in Japan, is studied. Several well-known classifiers combined with PCA have been used. Noticeable improvement in the results is reported. |
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Octubre de 2017 Large earthquakes on subduction zone plate boundary megathrusts result from intervals of strain accumulation and release. The mechanism diversity and spatial distribution of moderate-size aftershocks is influenced by the mainshock rupture depth extent. Mainshocks that rupture across the shallow megathrust to near the trench have greater intraplate aftershock faulting diversity |
than events with rupture confined to deeper portions of the megathrust. Diversity of intraplate aftershock faulting also increases as the size of the mainshock approaches the largest size event to have ruptured that region of the megathrust. Based on these tendencies, we identify “breakthrough” ruptures as those involving shallow rupture of the megathrust with volumetrically extensive elastic strain drop around the plate boundary that allows activation of diverse intraplate faulting influenced by long-term ambient deformation stresses. In contrast, homogeneity of the aftershock faulting mechanisms indicates only partial release of elastic strain energy and remaining potential for another large rupture. | |||
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Octubre de 2017 Mars is believed to have possessed
a dynamo that ceased operating approximately 4 Ga ago, although the
exact time is still under debate. The scope of this study is to constrain
the possible timing of its cessation by studying the magnetization
signatures of craters. The study uses the latest available model of
the lithospheric magnetic field of Mars, which is based on Mars Global
Surveyor data. We tackle the problem of non-uniqueness that characterises
the inversion of magnetic field data for the magnetization by inferring
only the visible part of the magnetization, i.e., the part of the
magnetization that gives rise to |
the observed magnetic field. Further on, we demonstrate that a zero visible magnetization is a valid proxy for the entire magnetization being zero under the assumption of a magnetization distribution of induced geometry. This assumption holds for craters whose thermoremanent magnetization has not been significantly altered since its acquisition. Our results show that the dynamo shut off after the impacts that created the Acidalia and SE Elysium basins and before the crust within the Utopia basin cooled below its magnetic blocking temperature. Accounting for the age uncertainties in the dating of these craters, we estimate that the dynamo shut off at an N(300) crater retention age of 2.5-3.2 or an absolute model age of 4.12 - 4.14 Ga. Moreover, the Martian dynamo may have been weaker in its early stage, which if true implies that the driving mechanism of the Martian dynamo was not the same throughout its history. | |||
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Octubre de 2017 Earthquake-induced landslide (EQIL)
inventories are essential tools to extend our knowledge of the relationship
between earthquakes and the landslides they can trigger. Regrettably,
such inventories are difficult to generate and therefore scarce, and
the available ones differ in terms of their quality and level of completeness.
Moreover, access to existing EQIL inventories is currently difficult
because there is no centralized database. To address these issues,
we compiled EQIL inventories from around the globe based on an extensive
literature study. The database contains information on 363 landslide-triggering
earthquakes and includes 66 digital landslide inventories. To make
these data openly available, we created a repository to host the digital |
inventories that we have permission to redistribute through the U.S. Geological Survey ScienceBase platform. It can grow over time as more authors contribute their inventories. We analyze the distribution of EQIL events by time period and location, more specifically breaking down the distribution by continent, country and mountain region. Additionally, we analyze frequency distributions of EQIL characteristics, such as the approximate area affected by landslides, total number of landslides, maximum distance from fault rupture zone, and distance from epicenter when the fault plane location is unknown. For the available digital EQIL inventories, we examine the underlying characteristics of landslide size, topographic slope, roughness, local relief, distance to streams, peak ground acceleration, peak ground velocity, and Modified Mercalli Intensity. Also, we present an evaluation system to help users assess the suitability of the available inventories for different types of EQIL studies and model development. | |||
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Septiembre de 2017 The largest observed earthquakes
occur on subduction interfaces and frequently cause widespread damage
and loss of life. Understanding the rupture behavior of megathrust
events is crucial for earthquake rupture physics, as well as for earthquake
early-warning systems. However, the large variability in behavior
between |
individual events seemingly defies a description with a simple unifying model. Here we use three source time function (STF) data sets for subduction zone earthquakes, with moment magnitude Mw = 7, and show that such large ruptures share a typical universal behavior. The median STF is scalable between events with different sizes, grows linearly, and is nearly triangular. The deviations from the median behavior are multiplicative and Gaussian—that is, they are proportionally larger for larger events. Our observations suggest that earthquake magnitudes cannot be predicted from the characteristics of rupture onsets. | |||
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Septiembre de 2017 We apply machine learning to data
sets from shear laboratory experiments, with the goal of identifying
hidden signals that precede earthquakes. Here we show that by listening
to the acoustic signal emitted by a laboratory fault, machine learning
can predict the time remaining |
before it fails with great accuracy. These predictions are based solely on the instantaneous physical characteristics of the acoustical signal and do not make use of its history. Surprisingly, machine learning identifies a signal emitted from the fault zone previously thought to be low-amplitude noise that enables failure forecasting throughout the laboratory quake cycle. We infer that this signal originates from continuous grain motions of the fault gouge as the fault blocks displace. We posit that applying this approach to continuous seismic data may lead to significant advances in identifying currently unknown signals, in providing new insights into fault physics, and in placing bounds on fault failure times. | |||
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Septiembre de 2017 Understanding the controlling mechanisms
underlying injection-induced seismicity is important for optimizing
reservoir productivity and addressing seismicity-related concerns
related to hydraulic stimulation in Enhanced Geothermal Systems. Hydraulic
stimulation enhances permeability through elevated pressures, which
cause normal deformations and the shear slip of pre-existing fractures.
Previous experiments |
indicate that fracture deformation in the normal direction reverses as the pressure decreases, e.g., at the end of stimulation. We hypothesize that this normal closure of fractures enhances pressure propagation away from the injection region and significantly increases the potential for post-injection seismicity. To test this hypothesis, hydraulic stimulation is modeled by numerically coupling flow in the fractures and matrix, fracture deformation and matrix deformation for a synthetic reservoir in which the flow and mechanics are strongly affected by a complex three-dimensional fracture network. The role of the normal closure of fractures is verified by comparing simulations conducted with and without the normal closure effect. | |||
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Septiembre de 2017 Recent observations suggested that
ionospheric anomalies appear immediately before large earthquakes
with moment magnitudes (Mw) of 8.2 or more. Do similar phenomena precede
smaller earthquakes? Here we answer this question by analyzing vertical
total electron contents (VTEC) observed near the epicenters before
and after 32 earthquakes with Mw7.0–8.0 using data from nearby Global
Navigation Satellite Systems stations. To detect anomalies, we |
defined the reference curves to fit the observed VTEC and considered the departure from the curves as anomalies. In estimating the reference curves, we excluded time windows, prescribed for individual earthquakes considering Mw, possibly affected by earthquakes. We validated the method using synthetic VTEC data assuming both preseismic, coseismic, and postseismic anomalies. Out of the 32 Mw7.0–8.0 earthquakes, eight earthquakes showed possible preseismic anomalies starting 10–20 min before earthquakes. For earthquakes of this Mw range, we can observe preseismic ionospheric changes probably when the background VTEC is large, say 50 TECU (total electron content unit, 1 TECU = 1016 el m-2) or more. | |||
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Septiembre de 2017 In a context of global change and
increasing anthropic pressure on the environment, monitoring the Earth
system and its evolution has become one of the key missions of geosciences.
Geodesy is the geoscience that measures the geometric shape of the
Earth, its orientation in space, and gravity field.Time-variable gravity,
because of its high accuracy, can be used to build an enhanced picture
and understanding of the changing Earth. Ground-based gravimetry can |
determine the change in gravity related
to the Earth rotation fluctuation, to celestial-body and Earth attractions,
to the mass in the direct vicinity of the instruments, and vertical
displacement of the instrument itself on the ground. In this paper, we review the geophysical questions that can be addressed byground gravimeters used to monitor time-variable gravity. This is done in relation to the instrumental characteristics, noise sources and good practices. We also discuss the next challenges to be met by ground gravimetry,the place that terrestrial gravimetry should hold in the Earth observation system, and perspectives and recommendations about the future of ground gravity instrumentation. |
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Septiembre de 2017 Field, geochemical, and geochronological
data show that the southern segment of the ancestral Cascades arc
advanced into the Oregon back-arc region from 30 to 20 Ma. We attribute
this event to thermal uplift of the Farallon slab by the |
Yellowstone mantle plume, with heat diffusion, decompression, and the release of volatiles promoting high-K calc-alkaline volcanism throughout the back-arc region. The greatest degree of heating is expressed at the surface by a broad ENE-trending zone of adakites and related rocks generated by melting of oceanic crust from the Farallon slab. A hiatus in eruptive activity began at ca. 22–20 Ma but ended abruptly at 16.7 Ma with renewed volcanism from slab rupture occurring in two separate regions. The eastern rupture resulted in the extrusion of Steens Basalt | |||
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Septiembre de 2017 We numerically compute seismoelectric wavefields generated at a fluid/porous medium interface by an explosive source in the fluid. Our numerical experiments show that electromagnetic (EM) signals accompanying the P, S, and interface waves can be observed at receivers located in the fluid regions near the interface. Such accompanying EM signals are produced by the inhomogeneous EM waves that are generated by the seismic waves at the interface and their amplitudes decrease with the distance from interface. Under the excitation of an explosive |
source whose strength is within the capability of industry air guns, electric and magnetic fields that accompany the Scholte wave are on the order of 1 μV/m and 0.01 nT, respectively. This means that the EM signals arising from the electrokinetic effect at an ocean bottom are detectable and suggest that it is possible to measure the EM signals during marine seismic explorations to study the properties of the seafloor material. EM signals that accompany the P, S, and interface waves are also observed in the porous medium region near the interface. Component analysis shows that they contain contributions from multiple modes of waves, among which the slow compressional wave contributes significantly to the vertical electric field, leading to a much stronger vertical electric field than the horizontal electric field during the passage of a seismic wave along the interface. | |||
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Septiembre de 2017 Landslides are the second most important
cause of tsunamis after earthquakes, and their potential for generating
large tsunamis depend on the slide process. Among the world's largest
submarine landslides is the Storegga Slide that generated a large
tsunami over an ocean-wide scale, while no traces of a tsunami generated
from the similar and nearby Trænadjupet Slide have been found. Previous
models for such landslide tsunamis have not been able to capture |
the complexity of the landslide processes and are at odds with geotechnical and geomorphological data that reveal retrogressive landslide development. The tsunami generation from these massive events are here modeled with new methods that incorporate complex retrogressive slide motion. We show that the tsunamigenic strength is closely related to the retrogressive development and explain, for the first time, why similar giant landslides can produce very different tsunamis, sometimes smaller than anticipated. Because these slide mechanisms are common for submarine landslides, modeling procedures for dealing with their associated tsunamis should be revised. | |||
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Septiembre de 2017 We investigate possible biasing effects of inaccurate timing corrections on teleseismic P-wave back-projection imaging of large earthquake ruptures. These errors occur because empirically-estimated time shifts based on aligning P-wave first arrivals are exact only at the hypocenter and provide approximate corrections for other parts of the rupture. Using the Japan subduction zone as a test region, we analyze 46 M6–7 earthquakes over a ten-year period, including many aftershocks of the 2011 M9 Tohoku earthquake, performing waveform cross-correlation of their initial P-wave arrivals to obtain hypocenter timing |
corrections to global seismic stations. We then compare back-projection images for each earthquake using its own timing corrections with those obtained using the time corrections from other earthquakes. This provides a measure of how well sub-events can be resolved with back-projection of a large rupture as a function of distance from the hypocenter. Our results show that back-projection is generally very robust and that the median sub-event location error is about 25 km across the entire study region (∼700 km). The back-projection coherence loss and location errors do not noticeably converge to zero even when the event pairs are very close (<20 km). This indicates that most of the timing differences are due to 3D structure close to each of the hypocenter regions, which limits the effectiveness of attempts to refine back-projection images using aftershock calibration, at least in this region. | |||
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Septiembre de 2017 This paper proposes a stochastic
approach to model the earthquake uncertainties in terms of the rupture
location and the slip distribution for a future event, with an expected
earthquake magnitude. Once the statistical properties of earthquake
uncertainties are described, they are then propagated into the tsunami
response and the inundation at assessed coastal areas. The slip distribution
is modeled as a random field within a nonrectangular rupture area.
The Karhunen-Lòeve (K-L) expansion method is used to generate samples
of the random slip, and a translation model is employed to obtain
target probability properties. A strategy is developed to specify
the accuracy of the random samples in |
terms of numbers of subfaults of the rupture area and the truncation of the K-L expansion. The propagation of uncertainty into the tsunami response is performed by means of a Stochastic Reduced Order Model. To illustrate the methodology, we investigated a study case in north Chile. We first demonstrate that the stochastic approach generates consistent earthquake samples with respect to the target probability properties. We also show that the results obtained from SROM are more accurate than those obtained with classic Monte Carlo simulations. To validate the methodology, we compared the simulated tsunamis and the tsunami records for the 2014 Chilean earthquake. Results show that leading wave measurements fall within the tsunami sample space. At later times, however, there are mismatches between measured data and the simulated results, suggesting that other sources of uncertainties are as relevant as the uncertainty of earthquakes. | |||
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Agosto de 2017 When a large earthquake occurs near an active volcano, there is often concern that volcanic eruptions may be triggered by the earthquake. In this study, recently accumulated, reliable data were analyzed to quantitatively evaluate the probability of the occurrence of new eruptions of volcanoes located near the epicenters of large earthquakes. For volcanoes located within 200 km of large earthquakes of magnitude 7.5 or |
greater, the eruption occurrence probability increases by approximately 50% for 5 years after the earthquake origin time. However, no significant increase in the occurrence probability of new eruptions was observed at distant volcanoes or for smaller earthquakes. The present results strongly suggest that new eruptions are likely triggered by static stress changes and/or strong ground motions caused by nearby large earthquakes. This is not similar to the previously presented evidence that volcanic earthquakes at distant volcanoes are remotely triggered by surface waves generated by large earthquakes. | |||
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Agosto de 2017 Earthquakes induced by natural gas extraction from the Groningen reservoir, the Netherlands, put local communities at risk. Responsible operation of a reservoir whose gas reserves are of strategic importance to the country requires understanding of the link between extraction and earthquakes. We synthesize observations and a model for Groningen seismicity to produce forecasts for felt seismicity (M > 2.5) in the period |
February 2017 to 2024. Our model accounts for poroelastic earthquake triggering and rupture on the 325 largest reservoir faults, using an ensemble approach to model unknown heterogeneity and replicate earthquake statistics. We calculate probability distributions for key model parameters using a Bayesian method that incorporates the earthquake observations with a nonhomogeneous Poisson process. Our analysis indicates that the Groningen reservoir was not critically stressed prior to the start of production. Epistemic uncertainty and aleatoric uncertainty are incorporated into forecasts for three different future extraction scenarios. The largest expected eart hquake was similar for all scenarios, with a 5% likelihood of exceeding M 4.0. | |||
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Agosto de 2017 Cosmochemical and geochemical studies
suggest sulfur (S) as a light alloying element in the iron-rich cores
of telluric planets, but there is no report of sulfur's alloying effect
on the electrical and thermal transport properties of iron (Fe); a
subject that is closely related to the dynamo |
action and thermal evolution of planetary cores. We measured the electrical resistivity of hexagonal-closed-packed (hcp) structured Fe alloy containing 3 wt. % silicon (Si) and 3 wt. % S up to 110 GPa at 300 K. Combined with the reported resistivities of hcp Fe and hcp Fe-Si alloy, we determined the impurity resistivity of S in a hcp Fe matrix at high pressures. The obtained impurity resistivity of S is found to be smaller than that of Si. Therefore, S is a weaker influence on the conductivity of Fe alloy, even if S is a major light element in the planetary cores. | |||
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Agosto de 2017 GNSS-based earthquake early warning (EEW) algorithms estimate fault-finiteness and unsaturated moment magnitude for the largest, most damaging earthquakes. Because large events are infrequent, algorithms are not regularly exercised and insufficiently tested on few available datasets. We use 1300 realistic, time-dependent, synthetic earthquakes on the Cascadia megathrust to rigorously test the |
Geodetic Alarm System. Solutions are reliable once six GNSS stations report static offsets, which we require for a “first alert.” Median magnitude and length errors are -0.15±0.24 units and -31±40% for the first alert, and -0.04±0.11 units and +7±31% for the final solution. We perform a coupled test of a seismic-geodetic EEW system using synthetic waveforms for a Mw8.7 scenario. Seismic point-source solutions result in severely underestimated PGA. Geodetic finite-fault solutions provide more accurate predictions at larger distances, thus increasing warning times. Hence, GNSS observations are essential in EEW to accurately characterize large (out-of-network) events and correctly predict ground motion. | |||
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Agosto de 2017 Thick, rigid continents move over
the weaker underlying mantle, although geophysical and geochemical
constraints on the exact thickness and defining mechanism of the continental
plates are widely discrepant. Xenoliths suggest a chemical continental
lithosphere ~175 kilometers thick, whereas seismic tomography supports
a |
much thicker root (>250 kilometers) and a gradual lithosphere-asthenosphere transition, consistent with a thermal definition. We modeled SS precursor waveforms from continental interiors and found a 7 to 9% velocity drop at depths of 130 to 190 kilometers. The discontinuity depth is well correlated with the origin depths of diamond-bearing xenoliths and corresponds to the transition from coarse to deformed xenoliths. At this depth, the xenolith-derived geotherm also intersects the carbonate-silicate solidus, suggesting that partial melt defines the plate boundaries beneath the continental interior. | |||
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Agosto de 2017 Real-time ground motion alerts,
as can be provided by Earthquake Early Warning (EEW) systems, need
to be both timely and sufficiently accurate to be useful. Yet how
timely and how accurate the alerts of existing EEW algorithms are
is often poorly understood. In part, this is because EEW algorithm
performance is usually evaluated not in terms of ground motion prediction
accuracy and timeliness but in terms of other metrics (e.g., magnitude
and location estimation errors), which do not directly reflect the
usefulness of the alerts from an end user perspective. Here we attempt
to |
identify a suite of metrics for EEW algorithm performance evaluation that directly quantify an algorithm's ability to identify target sites that will experience ground motion above a critical (user-defined) ground motion threshold. We process 15,553 recordings from 238 earthquakes with M > 5 (mostly from Japan and southern California) in a pseudo-real-time environment and investigate two end-member EEW methods. We use the metrics to highlight both the potential and limitations of the two algorithms and to show under which circumstances useful alerts can be provided. Such metrics could be used by EEW algorithm developers to convincingly demonstrate the added value of new algorithms or algorithm components. They can complement existing performance metrics that quantify other relevant aspects of EEW algorithms (e.g., false event detection rates) for a comprehensive and meaningful EEW performance analysis. | |||
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Agosto de 2017 Aftershock activity depends at first
order on the main shock magnitude but also shows important fluctuations
between shocks of equal magnitude. We here investigate these fluctuations,
by quantifying them and by relating them to the main shock stress
drop and other variables, for |
southern California earthquakes. A method is proposed in order to only count directly triggered aftershocks, rather than secondary aftershocks (i.e., triggered by previous aftershocks), and to only quantify fluctuations going beyond the natural Poisson variability. Testing of the method subjected to various model errors allows to quantify its robustness. It is found that these fluctuations follow a distribution that is well fitted by a lognormal distribution, with a coefficient of variation of about 1.0 to 1.1. A simple model is proposed to relate this observed dependence to main shock stress drop variability. | |||
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Agosto de 2017 Continents have tolerated billions
of years of tectonic stresses and disfigurement, yet they continue
to survive. Compared with their oceanic counterpart, where a sinking
demise is an almost certainty, continents and their internal cores,
or cratons, are much thicker (>175 km), older (>2 billion years),
colder, and more buoyant. However, their basic attributes, such as
size and shape, are |
a still a matter of debate because of large uncertainties in deceivingly straightforward, but entirely complicated, measurements. Continental cratons are rigid bodies composed of both crust and mantle, and their thickness was thought to be related to temperature and extend to depths of 250 to 350 km. On page 580 of this issue, Tharimena et al. (1) use reflections of seismic waves within the cratons to constrain their thickness globally. The strength of the reflections suggests that the base of the cratonic plate is defined by a partial melt of carbon-laced silicate mantle, not temperature. | |||
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Julio de 2017 The amplitude asymmetry and initial polarity of seismic induced ionospheric perturbations around the epicenter are considered to be important in providing information about the rupture propagation and related vertical surface deformation. To comprehend this, we study ionospheric perturbations related to the 12 May 2015, Mw 7.3 Nepal earthquake. We model the |
coseismic slip associated with the event using the interferometric synthetic aperture radar derived surface deformation data. The ionospheric perturbations associated with the obtained surface deformation are explained in terms of rupture propagation, favorable geomagnetic field-wave coupling, and satellite geometry effects. We discuss the effects of phase cancelation on the perturbation evolution for various receiver satellite line-of-sight configurations invoking an elementary version of satellite geometry factor. The present study thus elucidates further the role of nontectonic forcing mechanisms while identifying ground source pattern using the associated ionospheric perturbations. | |||
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Julio de 2017 Ultralow-velocity zones are localized regions of extreme material properties detected seismologically at the base of Earth's mantle. Their nature and role in mantle dynamics are poorly understood. We used shear waves diffracted at the core-mantle boundary to |
illuminate the root of the Iceland plume from different directions. Through waveform modeling, we detected a large ultralow-velocity zone and constrained its shape to be axisymmetric to a very good first order. We thus attribute it to partial melting of a locally thickened, denser- and hotter-than-average layer, reflecting dynamics and elevated temperatures within the plume root. Such structures are few and far apart, and they may be characteristic of the roots of some of the broad mantle plumes tomographically imaged within the large low-shear-velocity provinces in the lower mantle. | |||
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Julio de 2017 The ultimate goal of volcanology
is forecasting eruptions. This task is particularly challenging at
calderas, where unrest is frequent, affects wider areas and its evidence
is often masked by the activity of hydrothermal systems. A recent
study has compiled a database on caldera unrest, derived from seismicity,
geodetic, gravity, and geochemical monitoring data at calderas worldwide,
from 1988 to 2014. Here we exploit this database, searching for the
most recurring features of unrest and, in turn, its possible dynamics.
In particular, we focus on (a) the duration of unrest at calderas;
(b) recurring patterns in unrest; (c) unrest episodes culminating
in eruptions, including time-predictability or size-predictability
and a |
multivariate regression analysis. Our analysis indicates that preeruptive unrest is shorter than noneruptive unrest, particularly with open or semiplugged calderas, calderas with mafic or mixed composition of past eruptive products, or unrest driven by mafic magma; conversely, lack of data on preeruptive unrest driven by felsic magma and/or at felsic or plugged calderas prevents an analysis of these specific subsets. In addition, 72% of preeruptive unrest lasts <10 months and shows high seismicity and degassing. The remaining 28% (a) is essentially aseismic in calderas with open-conduit (17%), or (b) lasts between 10 and 18 months, with seismicity and degassing, constituting a longer-duration tail of the preeruptive unrest with seismicity and degassing (11%). Surface deformation is not always reliable to characterize preeruptive unrest. Our analysis suggests that magma may withstand only a limited period of “eruptability,” before becoming stored in the upper crust. | |||
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Julio de 2017 Copahue volcano straddling the edge
of the Agrio-Caviahue caldera along the Chile-Argentina border in
the southern Andes has been in unrest since inflation began in late
2011. We constrain Copahue's source models with satellite and airborne
interferometric synthetic aperture radar (InSAR) deformation observations.
InSAR time series from descending track RADARSAT-2 and COSMO-SkyMed
data span the entire inflation period from 2011 to 2016, with their
initially high rates of 12 and 15 cm/yr, respectively, slowing only
slightly despite ongoing small eruptions through 2016. InSAR ascending
and descending track time series for the 2013–2016 time period |
constrain a two-source compound dislocation model, with a rate of volume increase of 13 × 106 m3/yr. They consist of a shallow, near-vertical, elongated source centered at 2.5 km beneath the summit and a deeper, shallowly plunging source centered at 7 km depth connecting the shallow source to the deeper caldera. The deeper source is located directly beneath the volcano tectonic seismicity with the lower bounds of the seismicity parallel to the plunge of the deep source. InSAR time series also show normal fault offsets on the NE flank Copahue faults. Coulomb stress change calculations for right-lateral strike slip (RLSS), thrust, and normal receiver faults show positive values in the north caldera for both RLSS and normal faults, suggesting that northward trending seismicity and Copahue fault motion within the caldera are caused by the modeled sources. Together, the InSAR-constrained source model and the seismicity suggest a deep conduit or transfer zone where magma moves from the central caldera to Copahue's upper edifice. | |||
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Julio de 2017 On 25 December 2016, the Mw 7.6 Chiloé earthquake broke a plate boundary asperity in south central Chile near the center of the rupture zone of the Mw 9.5 Valdivia earthquake of 1960. To gain insight on decadal-scale deformation trends and their relation with the Chiloé earthquake, we combine geodetic, teleseismic, and regional seismological data. GPS velocities increased at continental scale after the 2010 |
Maule earthquake, probably due to a readjustment in the mantle flow and an apparently abrupt end of the viscoelastic mantle relaxation following the 1960 Valdivia earthquake. It also produced an increase in the degree of plate locking. The Chiloé earthquake occurred within the region of increased locking, breaking a circular patch of ~15 km radius at ~30 km depth, located near the bottom of the seismogenic zone. We propose that the Chiloé earthquake is a first sign of the seismic reawakening of the Valdivia segment, in response to the interaction between postseismic viscoelastic relaxation and changes of interseismic locking between Nazca and South America. | |||
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Julio de 2017 To explore where earthquakes tend to recur, we statistically investigated repeating earthquake catalogs and background seismicity from different regions (Parkfield, Hayward, Calaveras, and Chihshang Faults). We show that the location of repeating earthquakes can be mapped using the spatial distribution of the seismic a and b values |
obtained from the background seismicity. Molchan's error diagram statistically confirmed that repeating earthquakes occur within areas with high a values (2.8–3.8) and high b values (0.9–1.1) on both strike-slip and thrust fault segments. However, no significant association held true for fault segments with more complicated geometry or for wider areas with a complex fault network. The productivity of small earthquakes responsible for high a and b values may thus be the most important factor controlling the location of repeating earthquakes. We inferred that the location of high creep rate in planar/listric fault structures might be indicated by a values of ~3 and b values of ~1. | |||
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Julio de 2017 Recent observations suggested that ionospheric anomalies appear immediately before large earthquakes with moment magnitudes (Mw) of 8.2 or more. Do similar phenomena precede smaller earthquakes? Here we answer this question by analyzing vertical total electron contents (VTEC) observed near the epicenters before and after 32 earthquakes with Mw7.0-8.0 using data from nearby Global Navigation Satellite |
System (GNSS) stations. To detect anomalies, we defined the reference curves to fit the observed VTEC, and considered the departure from the curves as anomalies. In estimating the reference curves, we excluded time windows, prescribed for individual earthquakes considering Mw, possibly affected by earthquakes. We validated the method using synthetic VTEC data assuming both pre-, co- and postseismic anomalies. Out of the 32 Mw7.0-8.0 earthquakes, 8 earthquakes showed possible preseismic anomalies starting 10-20 minutes before earthquakes. For earthquakes of this Mw range, we can observe preseismic ionospheric changes probably when the background VTEC is large, say 50 TECU or more. | |||
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Julio de 2017 The Volcanic Explosivity Index (VEI) 5 eruption of the Puyehue-Cordón Caulle volcanic complex (PCC) in central Chile, which began 4 June 2011, provides a rare opportunity to assess the rapid transport and deposition of sulfate and ash from a mid-latitude volcano to the Antarctic ice sheet. We present sulfate, microparticle concentrations of fine-grained (~5 μm diameter) tephra, and major oxide geochemistry, which document the depositional sequence of volcanic products from the PCC eruption in West Antarctic snow and shallow firn. From the depositional phasing and duration of ash and sulfate peaks, we infer that transport occurred primarily through the troposphere but that ash and sulfate transport |
were decoupled. We use Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) back-trajectory modeling to assess atmospheric circulation conditions in the weeks following the eruption, and find that conditions favored southward air parcel transport during 6-14 June and 4-18 July, 2011. We suggest that two discrete pulses of cryptotephra deposition relate to these intervals, and as such, constrain the sulfate transport and deposition lifespan to the ~2-3 weeks following the eruption. Finally, we compare PCC depositional patterns to those of prominent low- and high-latitude eruptions in order to improve multiparameter-based efforts to identify “unknown source” eruptions in the ice core record. Our observations suggest that mid-latitude eruptions such as PCC can be distinguished from explosive tropical eruptions by differences in ash/sulfate phasing and in the duration of sulfate deposition, and from high-latitude eruptions by differences in particle size distribution and in cryptotephra geochemical composition. | |||
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Junio de 2017 On 16 September 2015, a Mw 8.3
earthquake ruptured the subduction zone offshore of Illapel, Chile,
generating an aftershock sequence with 14 Mw 6.0–7.0 events. A double
source W phase moment tensor inversion consists of a Mw 7.2 subevent
and the main Mw 8.2 phase. We determine two slip models for the mainshock,
one using teleseismic broadband waveforms and the other using static
GPS and InSAR surface displacements, which indicate high slip north
of the epicenter and west-northwest of the epicenter near the oceanic
trench. These models and slip distributions published in other studies
suggest spatial slip uncertainties of ~25 km and have |
peak slip values that vary by a factor of 2. We relocate aftershock hypocenters using a Bayesian multiple-event relocation algorithm, revealing a cluster of aftershocks under the Chilean coast associated with deep (20–45 km depth) mainshock slip. Less vigorous aftershock activity also occurred near the trench and along strike of the main aftershock region. Most aftershocks are thrust-faulting events, except for normal-faulting events near the trench. Coulomb failure stress change amplitudes and signs are uncertain for aftershocks collocated with deeper mainshock slip; other aftershocks are more clearly associated with loading from the mainshock. These observations reveal a frictionally heterogeneous interface that ruptured in patches at seismogenic depths (associated with many aftershocks) and with homogeneous slip (and few aftershocks) up to the trench. This event likely triggered seismicity separate from the main slip region, including along-strike events on the megathrust and intraplate extensional events. | |||
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Junio de 2017 To explore where earthquakes tend
to recur, we statistically investigated repeating earthquake catalogs
and background seismicity from different regions (Parkfield, Hayward,
Calaveras, and Chihshang Faults). We show that the location of repeating
earthquakes can be mapped using the spatial distribution of the seismic
a and b values |
obtained from the background seismicity. Molchan's error diagram statistically confirmed that repeating earthquakes occur within areas with high a values (2.8–3.8) and high b values (0.9–1.1) on both strike-slip and thrust fault segments. However, no significant association held true for fault segments with more complicated geometry or for wider areas with a complex fault network. The productivity of small earthquakes responsible for high a and b values may thus be the most important factor controlling the location of repeating earthquakes. We inferred that the location of high creep rate in planar/listric fault structures might be indicated by a values of ~3 and b values of ~1. | |||
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Junio de 2017 Once the terrestrial planets had mostly completed their assembly, bombardment continued by planetesimals left over from accretion. Highly siderophile element (HSE) abundances in Mars' mantle imply that its late accretion supplement was 0.8 wt %; Earth and the Moon obtained an additional 0.7 wt % and 0.02 wt %, respectively. |
The disproportionately high Earth/Moon accretion ratio is explicable by stochastic addition of a few remaining Ceres-sized bodies that preferentially targeted Earth. Here we show that Mars' late accretion budget also requires a colossal impact, a plausible visible remnant of which is the emispheric dichotomy. The addition of sufficient HSEs to the Martian mantle entails an impactor of at least 1200 km in diameter to have struck Mars before ~4430 Ma, by which time crust formation was well underway. Thus, the dichotomy could be one of the oldest geophysical features of the Martian crust. Ejected debris could be the source material for its satellites. | |||
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