Showing papers on "Hypocenter published in 2017"
TL;DR: The 3 September 2016, Mw 5.8 Pawnee earthquake was the largest recorded earthquake in the state of Oklahoma as mentioned in this paper, which is part of an unprecedented increase in the earthquake rate in Oklahoma that is largely considered the result of the deep injection of waste fluids from oil and gas production.
Abstract: The 3 September 2016, Mw 5.8 Pawnee earthquake was the largest recorded earthquake in the state of Oklahoma. Seismic and geodetic observations of the Pawnee sequence, including precise hypocenter locations and moment tensor modeling, shows that the Pawnee earthquake occurred on a previously unknown left-lateral strike-slip basement fault that intersects the mapped right-lateral Labette fault zone. The Pawnee earthquake is part of an unprecedented increase in the earthquake rate in Oklahoma that is largely considered the result of the deep injection of waste fluids from oil and gas production. If this is, indeed, the case for the M5.8 Pawnee earthquake, then this would be the largest event to have been induced by fluid injection. Since 2015, Oklahoma has undergone wide-scale mitigation efforts primarily aimed at reducing injection volumes. Thus far in 2016, the rate of M3 and greater earthquakes has decreased as compared to 2015, while the cumulative moment—or energy released from earthquakes—has increased. This highlights the difficulty in earthquake hazard mitigation efforts given the poorly understood long-term diffusive effects of wastewater injection and their connection to seismicity.
143 citations
TL;DR: The results suggest that the Pawnee earthquake is a result of interplay among injection, tectonic faults, and foreshocks, suggesting a possible role of elastic stress transfer and critical stress state of the fault.
Abstract: The Pawnee M5.8 earthquake is the largest event in Oklahoma instrument recorded history. It occurred near the edge of active seismic zones, similar to other M5+ earthquakes since 2011. It ruptured a previously unmapped fault and triggered aftershocks along a complex conjugate fault system. With a high-resolution earthquake catalog, we observe propagating foreshocks leading to the mainshock within 0.5 km distance, suggesting existence of precursory aseismic slip. At approximately 100 days before the mainshock, two M ≥ 3.5 earthquakes occurred along a mapped fault that is conjugate to the mainshock fault. At about 40 days before, two earthquakes clusters started, with one M3 earthquake occurred two days before the mainshock. The three M ≥ 3 foreshocks all produced positive Coulomb stress at the mainshock hypocenter. These foreshock activities within the conjugate fault system are near-instantaneously responding to variations in injection rates at 95% confidence. The short time delay between injection and seismicity differs from both the hypothetical expected time scale of diffusion process and the long time delay observed in this region prior to 2016, suggesting a possible role of elastic stress transfer and critical stress state of the fault. Our results suggest that the Pawnee earthquake is a result of interplay among injection, tectonic faults, and foreshocks.
79 citations
TL;DR: In this paper, a series of experimental tests, under constant loading rates ranging from 0.01mm/s to 1 mm/s and under a fixed normal stress of 6.7 MPa, are performed to simulate conditions with changing strain rates.
55 citations
TL;DR: A detailed P-wave tomography of the deep earthquake source zone using a large number of arrival-time data shows that this large deep event occurred within the subducting Pacific slab which is penetrating into the lower mantle.
Abstract: On 30 May 2015 an isolated deep earthquake (~670 km, Mw 7.9) occurred to the west of the Bonin Islands. To clarify its causal mechanism and its relationship to the subducting Pacific slab, we determined a detailed P-wave tomography of the deep earthquake source zone using a large number of arrival-time data. Our results show that this large deep event occurred within the subducting Pacific slab which is penetrating into the lower mantle. In the Izu-Bonin region, the Pacific slab is split at ~28° north latitude, i.e., slightly north of the 2015 deep event hypocenter. In the north the slab becomes stagnant in the mantle transition zone, whereas in the south the slab is directly penetrating into the lower mantle. This deep earthquake was caused by joint effects of several factors, including the Pacific slab's fast deep subduction, slab tearing, slab thermal variation, stress changes and phase transformations in the slab, and complex interactions between the slab and the ambient mantle.
49 citations
TL;DR: In this paper, the authors deployed a local seismic network and purchased nearby active-source seismic reflection data to capture additional events, characterize the causative fault, and explore potential links between ongoing industry activity and seismicity.
Abstract: On 7 May 2015, a MW 4.0 earthquake occurred near Venus, northeast Johnson County, Texas, in an area of the Bend Arch-Fort Worth Basin that reports long-term, high-volume wastewater disposal and that has hosted felt earthquakes since 2009. In the weeks following the MW 4.0 earthquake, we deployed a local seismic network and purchased nearby active-source seismic reflection data to capture additional events, characterize the causative fault, and explore potential links between ongoing industry activity and seismicity. Hypocenter relocations of the resulting local earthquake catalog span ~4-6 km depth and indicate a fault striking ~230°, dipping to the west, consistent with a nodal plane of the MW 4.0 regional moment tensor. Fault plane solutions indicate normal faulting, with B-axes striking parallel to maximum horizontal compressive stress. Seismic reflection data image the reactivated basement fault penetrating the Ordovician disposal layer and Mississippian production layer, but not displacing post-Lower Pennsylvanian units. Template matching at regional seismic stations indicates that low magnitude earthquakes with similar waveforms began in April 2008, with increasing magnitude over time. Pressure data from five saltwater disposal wells within 5 km of the active fault indicate a disposal formation that is 0.9-4.8 MPa above hydrostatic. We suggest that the injection of 28,000,000 m3 of wastewater between 2006 and 2015 at these wells led to an increase in subsurface pore fluid pressure that contributed to inducing this long-lived earthquake sequence. The 2015 MW 4.0 event represents the largest event in the continuing evolution of slip on the causative fault.
42 citations
TL;DR: In this article, an asymmetric extensional pattern characterized by low-angle, E and NNE-dipping faults, and by antithetic, high-angle and SW-to-WSW-Dipping faults was reconstructed.
36 citations
TL;DR: In this paper, a detailed multiple-event hypocenter relocation analysis of the Mw 7.8 Gorkha Nepal earthquake sequence, constrained by local seismic stations, and a geodetic rupture model based on InSAR and GPS data is presented.
35 citations
TL;DR: In this paper, the authors investigate the effect of inaccurate timing corrections on teleseismic P-wave back-projection imaging of large earthquake ruptures, and they show that the backprojection coherence loss and location errors do not noticeably converge to zero even when the event pairs are very close (<20 km).
Abstract: 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.
34 citations
TL;DR: In this paper, a review of earthquake predictability research aimed at realizing practical operational forecasting is presented, in particular, uncertainty lies in identifying whether abnormal phenomena are precursors to large earthquakes.
Abstract: Statistical methods and various models in time-space-magnitude parameter space of earthquakes are being developed to analyze seismic activity based on earthquake hypocenter catalogs that are routinely accumulated. Considering complex geophysical environments and uncertainties, we seek proper stochastic modeling that depends on the history of earthquake occurrences and relevant geophysical information for describing and forecasting earthquake activity. Also, we need empirical Bayesian models with many parameters in order to describe nonstationary or nonhomogeneous seismic activity. This review is concerned with earthquake predictability research aimed at realizing practical operational forecasting. In particular, uncertainty lies in identifying whether abnormal phenomena are precursors to large earthquakes. The predictability of such models can be examined by certain statistical criteria.
34 citations
TL;DR: Based on the elastic dislocation theory and a multi-layered lithospheric model, the authors calculated the Coulomb failure stress changes caused by the Wenchuan and Jiuzhaigou earthquakes, and analyzed the influence of the aftershock distribution and stress changes on the major faults in this region caused by a M 7.0 earthquake.
Abstract: On August 8, 2017, a M 7.0 earthquake occurred in Jiuzhaigou County, Sichuan Province, China, resulting in significant casualties and property damage. Therefore, it is critical to identify the areas of potential aftershocks before reconstruction and re-settling people to avoid future disasters. Based on the elastic dislocation theory and a multi-layered lithospheric model, we calculate the Coulomb failure stress changes caused by the Wenchuan and Jiuzhaigou earthquakes, discuss the relationship between the M w7.9 Wenchuan and M 7.0 Jiuzhaigou earthquakes, and analyze the influence of the aftershock distribution and stress changes on the major faults in this region caused by the Jiuzhaigou earthquake. The co- and post-seismic stress changes caused by the Wenchuan earthquake significantly increased the stress accumulation at the hypocenter of the Jiuzhaigou earthquake. Therefore, the occurrence of the Jiuzhaigou earthquake was probably stimulated by the Wenchuan earthquake. The aftershock distribution is well explained by the co-seismic stress changes of the Jiuzhaigou earthquake. The stress accumulation and corresponding seismic hazard on the Maqu-Heye segment of the East Kunlun fault and the northern extremity of the Huya fault has been further increased by the Jiuzhaigou earthquake.
34 citations
TL;DR: In this paper, the authors used Synthetic Aperture Radar (SAR) data from the Copernicus Sentinel-1A and Sentinel−1B and Canadian RADARSAT-2 satellites with interferometric SAR analysis for the area of northcentral Oklahoma that surrounds Pawnee.
Abstract: The 3 September 2016 M w 5.8 Pawnee earthquake shook a large area of north‐central Oklahoma and was the largest instrumentally recorded earthquake in the state. We processed Synthetic Aperture Radar (SAR) from the Copernicus Sentinel‐1A and Sentinel‐1B and Canadian RADARSAT‐2 satellites with interferometric SAR analysis for the area of north‐central Oklahoma that surrounds Pawnee. The interferograms do not show phase discontinuities that would indicate surface ruptures during the earthquake. Individual interferograms have substantial atmospheric noise caused by variations in radar propagation delays due to tropospheric water vapor, so we performed a time‐series analysis of the Sentinel‐1 stack to obtain a more accurate estimate of the ground deformation in the coseismic time interval and the time variation of deformation before and after the earthquake. The time‐series fit for a step function at the time of the Pawnee shows about 3 cm peak‐to‐peak amplitude of the coseismic surface deformation in the radar line of sight with a spatial pattern that is consistent with fault slip on a plane trending east‐southeast. This fault, which we call the Sooner Lake fault, is parallel to the west‐northwest nodal plane of the U.S. Geological Survey National Earthquake Information Center moment tensor solution. We model the fault plane by fitting hypoDD‐relocated aftershocks aligned in the same trend. Our preferred slip model on this assumed fault plane, allowing only strike‐slip motion, has no slip shallower than 2.3 km depth, an area of moderate slip extending 7 km along strike between 2.3 and 4.5 km depth (which could be due to aftershocks and afterslip), and larger slip between 4.5 and 14 km depth extending about 12 km along strike. The large slip below the 4.5 km depth of our relocated hypocenter indicates that the coseismic rupture propagated down‐dip. The time‐series results do not show significant deformation before or after the earthquake above the high atmospheric noise level within about 40 km of the earthquake rupture.
Journal Article•
TL;DR: In this article, the authors performed joint inversions of strong motion, teleseismic, and geodetic data to investigate the rupture processes of three notable (Mw≥ 6.0) events of the 2016 Kumamoto earthquake sequence.
Abstract: We performed joint inversions of strong motion, teleseismic, and geodetic data to investigate the rupture processes of three notable (Mw ≥ 6.0) events of the 2016 Kumamoto earthquake sequence. Multi-segment fault models for the three events were constructed based on focal mechanisms, hypocenter distributions of this sequence, and active faults, as well as geodetic features. The results reveal the spatial relationships between the slip distributions of the three events over complex fault planes. In the largest event, the rupture primarily propagated to a northeastern region along the Futagawa fault zone. The extreme pulse-like waveforms observed at the near-fault stations during the largest event can be attributed to the event's upward rupture directivity, slip rate, and the nearly simultaneous slip of two subparallel fault planes.
TL;DR: In this article, the authors examined the variability of long-period (T ≥ 1 ǫ s) earthquake ground motions from 3D simulations of M w  7 earthquakes on the Salt Lake City segment of the Wasatch fault zone, Utah, from a set of 96 rupture models.
Abstract: We examine the variability of long‐period ( T ≥1 s) earthquake ground motions from 3D simulations of M w 7 earthquakes on the Salt Lake City segment of the Wasatch fault zone, Utah, from a set of 96 rupture models with varying slip distributions, rupture speeds, slip velocities, and hypocenter locations. Earthquake ruptures were prescribed on a 3D fault representation that satisfies geologic constraints and maintained distinct strands for the Warm Springs and for the East Bench and Cottonwood faults. Response spectral accelerations (SA; 1.5–10 s; 5% damping) were measured, and average distance scaling was well fit by a simple functional form that depends on the near‐source intensity level SA 0 ( T ) and a corner distance R c :SA( R , T )=SA 0 ( T )(1+( R / R c )) −1 . Period‐dependent hanging‐wall effects manifested and increased the ground motions by factors of about 2–3, though the effects appeared partially attributable to differences in shallow site response for sites on the hanging wall and footwall of the fault. Comparisons with modern ground‐motion prediction equations (GMPEs) found that the simulated ground motions were generally consistent, except within deep sedimentary basins, where simulated ground motions were greatly underpredicted. Ground‐motion variability exhibited strong lateral variations and, at some sites, exceeded the ground‐motion variability indicated by GMPEs. The effects on the ground motions of changing the values of the five kinematic rupture parameters can largely be explained by three predominant factors: distance to high‐slip subevents, dynamic stress drop, and changes in the contributions from directivity. These results emphasize the need for further characterization of the underlying distributions and covariances of the kinematic rupture parameters used in 3D ground‐motion simulations employed in probabilistic seismic‐hazard analyses. Electronic Supplement: Description of seismic‐velocity model and wave propagation code and interpretation of directivity effects, and figures of fault geometry, Z1 and Z2.5 depths, effects of rupture speed variations on directivity effects and amplifications.
TL;DR: In this article, the authors investigated spatiotemporal change in the interplate seismic activity following the 2011 Tohoku-oki earthquake (M9.0) in the region where interseismic interplate coupling was relatively weak and large postseismics slip was observed.
Abstract: We investigated spatiotemporal change in the interplate seismic activity following the 2011 Tohoku-oki earthquake (M9.0) in the region where interseismic interplate coupling was relatively weak and large postseismic slip was observed. We classified earthquakes by their focal mechanisms to identify the interplate events and conducted hypocenter relocation to examine the detailed spatiotemporal distribution of interplate earthquakes in the mostly creeping area. The results show that many interplate earthquakes, including M~6 events, emerged immediately after the Tohoku-oki earthquake in areas where very few interplate earthquakes had been observed in the 88 previous years. The emergent earthquakes include repeating sequences, and the extremely long quiescence of small to moderate earthquakes before the Tohoku-oki earthquake suggests that the source areas for the post-M9 events slipped aseismically during the quiescence. The repeaters’ magnitudes decayed over time following the Tohoku-oki earthquake and some sequences disappeared within a year. The emergence of interplate earthquakes suggests that areas where aseismic slip had been dominant before the Tohoku-oki earthquake, started to cause seismic slip after the earthquake, probably due to the increased loading rate from the afterslip. The magnitude decrease and disappearance of repeaters can be interpreted as shrinkage in seismic areas around the repeaters’ sources as the loading rate decreased due to the afterslip decay over time. These observations suggest that changes in the loading rate can cause slip behavior transition between seismic and aseismic. This indicates that such loading-rate-dependent slip behavior plays an important role in the spatiotemporal distribution of earthquakes in interplate seismogenic zones.
TL;DR: A seismic source model for the Mw 8.1 2017 Chiapas, Mexico, earthquake was constructed by kinematic waveform inversion using globally observed teleseismic waveforms, suggesting that the earthquake was a normalfaulting event on a steeply dipping plane, with the major slip concentrated around a relatively shallow depth of 28 km as mentioned in this paper.
Abstract: A seismic source model for the Mw 8.1 2017 Chiapas, Mexico, earthquake was constructed by kinematic waveform inversion using globally observed teleseismic waveforms, suggesting that the earthquake was a normal-faulting event on a steeply dipping plane, with the major slip concentrated around a relatively shallow depth of 28 km. The modeled rupture evolution showed unilateral, down-dip propagation northwestward from the hypocenter, and the down-dip width of the main rupture was restricted to less than 30 km below the slab interface, suggesting that the down-dip extensional stresses due to the slab bending were the primary cause of the earthquake. The rupture front abruptly decelerated at the northwestern end of the main rupture where it intersected the subducting Tehuantepec Fracture Zone, suggesting that the fracture zone may have inhibited further rupture propagation.
TL;DR: The authors showed that foreshocks initially rupture faults and fractures throughout the 300-meter-thick fault damage zone, and later localize onto a narrower zone (<100m) nearer the mainshock hypocenter.
Abstract: Foreshocks may provide a precursory signal of an impending earthquake, but their role in nucleation of the mainshock is unclear. One way to further our understanding of foreshock failure mechanisms is to determine where they occur in the fault zone. However, earthquake locations commonly include uncertainties large enough to allow rupture on either the main fault interface or on subsidiary fractures within a surrounding damage zone. Here we obtain precise earthquake locations, with ~10 m uncertainty, for foreshocks and aftershocks of an Mw5.0 near Prague, OK, USA. Repeating earthquakes imply that some precursory slow slip occurred before the mainshock. In addition, we show that foreshocks initially rupture faults and fractures throughout the 300-meter-thick fault damage zone, and later localize onto a narrower zone (<100 m thick) nearer the mainshock hypocenter. Focal mechanisms corroborate that foreshocks occur in the surrounding damage zone as well as on the mainshock rupture interface. These results highlight that earthquake nucleation is most likely a complex feedback between frictional failure processes on the fault interface and deformation in the surrounding damaged rock, not just nucleation on a single surface.
TL;DR: In this article, a high-resolution catalog called the "Japan Unified hIgh-resolution relocated catalog for earthquakes" (JUICE) was generated to evaluate the geometry and seismogenic depth of active faults in Japan.
TL;DR: In this article, the authors investigate the stress interaction between the Watchorn, Labette, and Sooner Lake fault systems and the effect of precursory activities on the 3 September 2016 M w ǫ 5.8 Pawnee earthquake.
Abstract: We investigate the stress interaction between the Watchorn, Labette, and Sooner Lake fault systems and the effect of precursory activities on the 3 September 2016 M w 5.8 Pawnee earthquake. We obtain fault‐plane solutions for earthquakes with sufficient azimuthal coverage using the HASH algorithm, and then perform coulomb stress analysis on both seismogenic faults and individual nodal planes. Our results found that the three M w ≥3.0 foreshocks exerted a cumulative coulomb stress change increase of 0.68–1.98 bars at the mainshock hypocenter and also promoted failure for most aftershocks within 2 km of the mainshock. The coulomb stress change of 5 bars exerted by the mainshock also promoted failure for most aftershocks within the conjugate fault system. The results suggest that earthquake interaction should be fully considered in hazard assessment for induced seismicity.
TL;DR: In this article, the authors analyzed the hypocenters and focal mechanisms of the aftershocks following the 2000 Western Tottori Earthquake, which occurred in the western part of Japan, using data from dense seismic observations.
Abstract: In order to clarify the origin of aftershocks, we precisely analyze the hypocenters and focal mechanisms of the aftershocks following the 2000 Western Tottori Earthquake, which occurred in the western part of Japan, using data from dense seismic observations. We investigate whether aftershocks occur on the mainshock fault plane on which coseismic slip occurred or they represent the rupture of fractures surrounding the mainshock fault plane. Based on the hypocenter distribution of the aftershocks, the subsurface fault structure of the mainshock is estimated using principal component analysis. As a result, we can obtain the detail fault structure composed of 8 best-fit planes. We demonstrate that the aftershocks around the mainshock fault are distributed within zones of 1.0–1.5 km in thicknesses, and their focal mechanisms are significantly diverse. This result suggests that most of the aftershocks represent the rupture of fractures surrounding the mainshock fault rather than the rerupture of the mainshock fault. The aftershocks have a much wider zone compared with the exhumed fault zone in field observations, suggesting that many aftershocks occur outside the fault damage zone. We find that most aftershocks except in and around the large-slip region are well explained by coseismic stress changes. These results suggest that the thickness of the aftershock distribution may be controlled by the stress changes caused by the heterogeneous slip distribution during the mainshock. The aftershock is also distributed within a much wider zone than the hypocenter distribution observed in swarm activity in the geothermal region, which is thought to be caused by the migration of hydrothermal fluid. This result implies a difference in generation processes: Stress changes due to the mainshock contribute primarily to the occurrence of aftershocks, whereas earthquake swarms in the geothermal region are caused by fluid migration within the localized zone.
TL;DR: In this paper, the source rupture process of the 2016 central Tottori, Japan, earthquake was estimated from strong motion waveforms using a multiple-time-window kinematic waveform inversion.
Abstract: The source rupture process of the 2016 central Tottori, Japan, earthquake (M
JMA 6.6) was estimated from strong motion waveforms using a multiple-time-window kinematic waveform inversion. A large slip region with a maximum slip of 0.6 m extends from the hypocenter to the shallower part, caused by the first rupture propagating upward 0–3 s after rupture initiation. The contribution of this large slip region to the seismic waves in the frequency band of the waveform inversion is significant at all stations. Another large slip region with smaller slips was found in north-northwest of the hypocenter, caused by the second rupture propagating in the north-northwest direction at 3–5 s. Although the contribution of this slip region is not large, seismic waveforms radiating from it are necessary to explain the later part of the observed waveforms at several stations with different azimuths. The estimated seismic moment of the derived source model is 2.1 × 1018 Nm (M
w 6.1). The high-seismicity area of aftershocks did not overlap with large-slip areas of the mainshock. Two wave packets in the high frequency band observed at near-fault stations are likely to correspond to the two significant ruptures in the estimated source model.
TL;DR: Wang et al. as mentioned in this paper conducted a comprehensive analysis of geophysical data and found that the deep seismogenic environment in the North China extensional tectonic region is generally characterized by a low-velocity anomalous belt beneath the hypocenter, inconsistency of the deep and shallow structures in the crust, a steep crustalal scale fault, relative lower velocities in the uppermost mantle, and local Moho uplift, etc.
Abstract: From the 1960s to 1970s, North China has been hit by a series of large earthquakes. During the past half century, geophysicists have carried out numerous surveys of the crustal and upper mantle structure, and associated studies in North China. They have made significant progress on several key issues in the geosciences, such as the crustal and upper mantle structure and the seismogenic environment of strong earthquakes. Deep seismic profiling results indicate a complex tectonic setting in the strong earthquake areas of North China, where a listric normal fault and a low-angle detachment in the upper crust coexist with a high-angle deep fault passing through the lower crust to the Moho beneath the hypocenter. Seismic tomography images reveal that most of the large earthquakes occurred in the transition between the high- and low-velocity zones, and the Tangshan earthquake area is characterized by a low-velocity anomaly in the middle-lower crust. Comprehensive analysis of geophysical data identified that the deep seismogenic environment in the North China extensional tectonic region is generally characterized by a low-velocity anomalous belt beneath the hypocenter, inconsistency of the deep and shallow structures in the crust, a steep crustalal-scale fault, relative lower velocities in the uppermost mantle, and local Moho uplift, etc. This indicates that the lithospheric structure of North China has strong heterogeneities. Geologically, the North China region had been a stable craton named the North China Craton or in brief the NCC, containing crustal rocks as old as ~3.8 Ga. The present-day strong seismic activity and the lower velocity of the lower crust in the NCC are much different from typical stable cratons around the world. These findings provide significant evidence for the destruction of the NCC. Although deep seismic profiling and seismic tomography have greatly enhanced knowledge about the deep-seated structure and seismogenic environment, some fundamental issues still remain and require further work.
TL;DR: In this article, the authors proposed the hypothesis that the area of the second event was stress loaded by the first one and that both the first and second earthquake events caused stress loading in the area, where the third event ruptured.
Abstract: On August 24, October 26 and 30, 2016, Central Apennines (Italy) were hit by three shallow, normal faulting very strong earthquakes rupturing in an NW–SE striking zone. Event 3 (Norcia) occurred between event 1 (Amatrice) at the SE and event 2 (Visso) at the NW of the entire rupture zone. The rupture histories of the three events, as revealed by teleseismic P-wave inversion, showed that all were characterized by bilateral rupture process with stronger rupture directivity towards NW for events 1 and 3 and towards SSE for event 2. Maximum seismic slip of 1.2, 0.8, and 1.4 m in the hypocenter and magnitude of M
w 6.2, 6.1, and 6.5 were calculated for the three events, respectively. DInSaR measurements based on Sentinel-1 and 2 satellite images showed ground deformation directivity from events 1 and 2 towards event 3, which is consistent with the rupture process directivity. For events 1, 2, and 3, the maximum ground subsidence was found equal to 0.2, 0.15, and 0.35 m. Based on rupture directivity and ground deformation pattern, we put forward the hypothesis that the area of the second event was stress loaded by the first one and that both the first and second earthquake events caused stress loading in the area, where the third event ruptured. Coulomb stress-transfer modelling yields strong evidence in favor of our hypothesis. The stress in the fault plane of event 2 was increased by ~0.19 bars due to loading from event 1. Event 3 fault plane was loaded by an amount of ~2 bars, due to the combined stress transfer from the two previous events, despite its proximity to the negative/positive lobe boundary. The three events produced combined stress loading of more than +0.5 bar along the Apennines to the NW and SE of the entire rupture zone. In the SE stress lobe, a series of strong earthquakes of M
w 5.3, 5.6, and 5.7 occurred on January 18, 2017, but likely, seismic potential remains in the area. We consider that in the NW and more extensive stress lobe, the seismic potential has also elevated due to stress loading.
TL;DR: In this article, the authors presented a kinematic slip model from the inversion of 1'Hz GPS, strong motion, and interferometric synthetic aperture radar (InSAR) data for the 2015 Mw6.5 Lefkada, Greece, earthquake.
Abstract: We present a kinematic slip model from the inversion of 1 Hz GPS, strong motion, and interferometric synthetic aperture radar (InSAR) data for the 2015 Mw6.5 Lefkada, Greece, earthquake. We will show that most of the slip during this event is updip of the hypocenter (10.7 km depth) with substantial slip (>0.5 m) between 5 km depth and the surface. The peak slip is ~1.6 m, and the inverted rake angles show predominantly strike-slip motion. Slip concentrates mostly to the south of the hypocenter, and the source time function indicates a total duration of ~17 s with peak moment rate at ~6 s. We will show that a 65° dipping geometry is the most plausible due to a lack of polarity reversals in the InSAR data and good agreement with Coulomb stress modeling, aftershock locations, and regional moment tensors. We also note that there was an ~20 cm peak-to-peak tsunami observed at one tide gauge station 300 km away from the earthquake. We will discuss tsunami modeling results and study the possible source of the amplitude discrepancy between the modeled and the observed data at far-field tide gauges.
TL;DR: In this article, the authors investigated 3D fault geometry over the transition from the partially coupled to the fully coupled plate interface inboard of the Nankai Trough off the Kii Peninsula, Japan and found that a gently dipping plate boundary decollement with a thick underthrust layer extends beneath the entire Kumano forearc basin.
TL;DR: Wang et al. as mentioned in this paper developed dynamic spontaneous rupture models of earthquakes on the Jiaocheng fault near Taiyuan, the capital and largest city of Shanxi Province in north China.
Abstract: Using the curved grid finite‐difference method, we develop dynamic spontaneous rupture models of earthquakes on the Jiaocheng fault (JF) near Taiyuan, the capital and largest city of Shanxi Province in north China. We then model the wave propagation and strong ground motion generated by these scenario earthquakes. A map of the seismic‐hazard distribution for a potential M 7.5 earthquake is created based on dynamic rupture and true 3D modeling. The tectonic initial stress fields derived from the inversion of focal mechanisms of historical earthquakes, a nonplanar fault, and a rough surface are considered in the dynamic rupture simulation. Based on the geological structure of the Taiyuan basin, normal faulting with a dipping angle of 60° is implemented for the scenario earthquake simulations. The largest uncertainty of a potential earthquake in the JF zone is the hypocenter. Four cases are used to nucleate the earthquake at different locations. Using these dynamic rupture sources for the JF, we further simulate and analyze both the seismic wave generated by the scenario earthquake and the strong ground motion. It is found that the low‐velocity media of the Taiyuan basin redistribute the ground motion well. The effects of the regional stress fields on the dynamic rupture and hazard distribution are investigated and discussed further. Moreover, a scenario earthquake, which can cause great damage to the city of Taiyuan, is modeled and analyzed.
TL;DR: In this article, the authors performed joint inversions of strong motion, teleseismic, and geodetic data to investigate the rupture processes of three notable (Mw≥ 6.0) events of the 2016 Kumamoto earthquake sequence.
Abstract: We performed joint inversions of strong motion, teleseismic, and geodetic data to investigate the rupture processes of three notable (Mw ≥ 6.0) events of the 2016 Kumamoto earthquake sequence. Multi-segment fault models for the three events were constructed based on focal mechanisms, hypocenter distributions of this sequence, and active faults, as well as geodetic features. The results reveal the spatial relationships between the slip distributions of the three events over complex fault planes. In the largest event, the rupture primarily propagated to a northeastern region along the Futagawa fault zone. The extreme pulse-like waveforms observed at the near-fault stations during the largest event can be attributed to the event's upward rupture directivity, slip rate, and the nearly simultaneous slip of two subparallel fault planes.
TL;DR: In this paper, travel time tomography using P- and S-wave arrival times of volcanic-tectonic (VT) events that occurred between November and December 2013 to determine the three-dimensional seismic velocity structure (Vp, Vs, and Vp/Vs) beneath Sinabung volcano, Indonesia in order to delineate geological subsurface structure and to enhance our understanding of the volcanism itself.
TL;DR: In this paper, the authors present a catalog of accurate epicenter coordinates of earthquakes located in the Gulf of California (GoC) in the period 2002-2014 that permits them to analyze the seismotectonics and to estimate the depth of the seismogenic zone of this region.
TL;DR: In this paper, a 6 borehole seismic network has been deployed recently in the Koyna region at depths of 981-1522m to improve the hypocenter locations.
TL;DR: In this paper, an early warning system for modern gravitational-wave observatories is described, which relies on near real-time earthquake alerts provided by the U.S. Geological Survey (USGS) and National Oceanic and Atmospheric Administration (NOAA).
Abstract: Ground-based gravitational wave interferometers such as the Laser Interferometer Gravitational-wave Observatory (LIGO) are susceptible to ground shaking from high-magnitude teleseismic events, which can interrupt their operation in science mode and significantly reduce their duty cycle. It can take several hours for a detector to stabilize enough to return to its nominal state for scientific observations. The down time can be reduced if advance warning of impending shaking is received and the impact is suppressed in the isolation system with the goal of maintaining stable operation even at the expense of increased instrumental noise. Here, we describe an early warning system for modern gravitational-wave observatories. The system relies on near real-time earthquake alerts provided by the U.S. Geological Survey (USGS) and the National Oceanic and Atmospheric Administration (NOAA). Preliminary low latency hypocenter and magnitude information is generally available in 5 to 20 min of a significant earthquake depending on its magnitude and location. The alerts are used to estimate arrival times and ground velocities at the gravitational-wave detectors. In general, 90% of the predictions for ground-motion amplitude are within a factor of 5 of measured values. The error in both arrival time and ground-motion prediction introduced by using preliminary, rather than final, hypocenter and magnitude information is minimal. By using a machine learning algorithm, we develop a prediction model that calculates the probability that a given earthquake will prevent a detector from taking data. Our initial results indicate that by using detector control configuration changes, we could prevent interruption of operation from 40 to 100 earthquake events in a 6-month time-period.