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The Türkiye-Syria earthquake doublet of 6 February 2023 (Mw 7.8 at 01:17 UTC and Mw 7.6 at 10:24 UTC) resulted in extensive damage and tens of thousands of casualties. We present the surface displacements of the two earthquakes from synthetic aperture radar (SAR) offset tracking measurements. We extracted the geometric parameters of the rupture faults from the surface displacements and early aftershock distribution, based on which we inverted the coseismic slip distributions. We then calculated Coulomb stress to investigate the triggering relationship between the earthquakes and stress transfer to neighbouring faults and regions. The coseismic ruptures of the earthquake doublet were predominantly left-lateral strike-slip motions distributed between 0 and 15 km depth. The maximum fault slip reached > 8 m (Mw 7.8) and almost 10 m (Mw 7.6). The coseismic deformation and fault slip motion are consistent with the overall westward extrusion of the Anatolian Plate relative to the Eurasian and Arabian plates. The Mw 7.8 earthquake increased Coulomb failure stress at the hypocenter of the Mw 7.6 earthquake, implying that the Mw 7.8 event had a strong positive causative effect. Moreover, coseismic stress perturbations revealed a positive Coulomb stress effect on the middle Puturge Fault, northern Dead Sea Fault Zone (DSFZ), Yesemek Fault, Antakya Fault, and Turkoglu Fault, indicating an increasing seismic hazard in these regions. [ABSTRACT FROM AUTHOR]

Abstract Mw 7.6 and Mw 7.4 earthquakes occurred 16 h apart on April 12 and April 13, 2014, at depths of 15 km and 35 km, respectively, southwest of Makira Island (San Cristobal) in the Solomon Islands. We study the source mechanisms to investigate the interrelation between the two events, and to investigate why the Solomon Islands have a historically high rate of doublet earthquakes. Teleseismic P waveform data for both events were used to obtain the slip distributions for the two earthquakes by a finite fault slip inversion method. The Mw 7.6 event is an east–west left-lateral strike slip, where the maximum slip is observed 8–24 km east of the hypocenter. The Mw 7.4 earthquake is a thrust event with north and south-dipping nodal planes. The fault plane is not clear from the aftershock distribution, but the north-dipping plane considered to be the likely fault plane because of the simpler slip distribution compared to the south-dipping plane. The static Coulomb failure stress changes caused by the first earthquake were calculated in the region of the second earthquake. The results show that there was a + 48.59 kPa change at the hypocenter for the assumed north-dipping plane and + 18.24 kPa for the assumed south-dipping plane of the Mw 7.4 event. The temporal pattern of aftershocks shows a possible rate increase of stress prior to the occurrence of the Mw 7.4 events, which may also contribute to the triggering of the second event by static Coulomb Stress changes. We propose a model that supports the geological complexity of the region that may encourage such doublet events. Graphical Abstract

Abstract The 2022 Mw6.2 Pasaman earthquake took place in central-west Sumatra in association with activity in the Sumatran Fault system. This study clarifies the spatial and temporal distribution of the Pasaman earthquake sequence and forecasts the earthquake sequence’s impact on the seismicity in the vicinity and in the Sumatran Fault system. We first examined the seismicity before the mainshock and observed temporal low b-value anomalies, shedding light on the earthquake’s precursor by monitoring b-values prior to the event. Based on the aftershocks in the first 18 days, we modeled the temporal distribution of the aftershocks according to the modified Omori’s law, which suggested this sequence could last 49–473 days. By further considering Båth’s law and the Gutenberg–Richter law, we estimated the temporal distribution of the maximum magnitudes in the aftershock sequence. To understand the spatial pattern of the aftershocks, we calculated the coseismic Coulomb stress change imparted by the Pasaman mainshock. Considering uncertainties of the Coulomb stress calculations from rupture geometry, mainshock parameters, friction coefficients, and strike angles of the receiver plane, the patterns of the Coulomb stress changes are similar that the stress increases extended northwest and southeast, consistent with aftershock distribution. We further evaluated rupture probability for each segment of the Sumatran Fault. Considering the stress perturbation imparted by the Pasaman earthquake, we expected a seismicity rate increase of ca. 40% at the Sumpur and Sianok segments in the short term. To quantify long-term rupture probability, the recurrence interval and the time elapsed since the previous earthquake were incorporated based on the time-dependent Brownian passage-time model. The earthquake probability at the Sumani segment in the coming 50 years was determined to be 72%. The results of this study have significant implications for subsequent probabilistic seismic hazard assessments, not only for Sumatra but also for certain metropolitan areas in Malaysia and Singapore.

There are two seismic gaps (Dayi seismic gap and Tianquan-Kangding seismic gap) on the Longmen Shan fault (LMSF), despite the successive occurrence of the 2008 Mw7.9 Wenchuan and 2013 Mw6.6 Lushan earthquakes. To analyze the effects of the Wenchuan and Lushan earthquakes on the LMSF (especially on seismic gaps along the LMSF) and regional seismic hazards, we calculate Coulomb stress changes caused by the Wenchuan and Lushan earthquakes based on a three-dimensional viscoelastic finite element model. Additionally, we calculate the spatial distribution of regional b-values based on the instrumental seismic catalog before the Wenchuan earthquake. By utilizing the inverse correlation between b-value and stress level, we infer the regional background stress level. The results show that regional earthquakes (including the 2008 Mw7.9 Wenchuan earthquake, 2013 Mw6.6 Lushan earthquake, 2014 Mw6.1 Kangding earthquake, 2017 Mw6.5 Jiuzhaigou earthquake, and 2022 Mw6.6 Luding earthquake) occurred in regions characterized by low b-values. Meanwhile, subsequent earthquakes occurred in regions where Coulomb stress changes caused by the Wenchuan and Lushan earthquakes were positive. This suggests that regions with both low b-values and positive Coulomb stress changes may pose higher seismic hazards. We found that there are four regions (southern Xianshuihe fault, Dongkunlun fault, northern Xiaojinhe fault, and Hanan-Qingshanwan fault) with both positive Coulomb stress changes caused by the Wenchuan and Lushan earthquakes and low b-values, which may indicate high stress accumulation and high seismic hazard in the future. The results also show that Coulomb stress changes caused by the Wenchuan and Lushan earthquakes increased significantly in the Dayi seismic gap (+ 0.216 ~ + 2.607 MPa) and Tianquan-Kangding seismic gap (+ 0.021 ~ + 0.211 MPa), while the result of the high b-values for the Dayi and Tianquan-Kangding seismic gaps indicate less background stress accumulation. However, with continued tectonic loading, seismic hazards on both seismic gaps should attract our attention. [ABSTRACT FROM AUTHOR]

On May 21, 2021, an Ms 6.4 earthquake occurred in Yangbi County, Yunnan Province, China. The epicenter was located on a secondary blind fault on the southwestern boundary of the Sichuan-Yunnan Block, and this area has a complex tectonic setting and seismogenic background. To improve the understanding of the seismogenic mechanism of this earthquake, we conduct an in-depth analysis on the regional stress and strain characteristics based on geodetic data from the Global Navigation Satellite System (GNSS) and seismological data (focal mechanism solutions) and analyze the stress changes at the epicenter of this earthquake from the perspective of stress triggering. The results show that the epicenter area of the Yangbi earthquake was characterized by significant shear and extension deformation, with a dextral shear rate of 2.5 × 10−8/a and an extension rate of 3.5 × 10−8/a. The present tectonic stress of the study area is dominated by NNW-directed principal compressive stress and NEE-directed principal extension stress, and the Yangbi main shock occurred on the optimal release nodal plane of the tectonic stress field where the relative shear stress reached 0.984. Furthermore, the cumulative Coulomb stress changes caused by four strong historical earthquakes exceeded the stress trigger threshold of 0.1 bar. All of these results suggest that the Yangbi Ms 6.4 earthquake was the result of the maximum effective shear stress concentration on the blind fault on the southwest side of the Weixi-Qiaohou fault, which was mainly driven by the regional tectonic stress and the surrounding historical strong earthquakes. [ABSTRACT FROM AUTHOR]

Mw 7.6 and Mw 7.4 earthquakes occurred 16 h apart on April 12 and April 13, 2014, at depths of 15 km and 35 km, respectively, southwest of Makira Island (San Cristobal) in the Solomon Islands. We study the source mechanisms to investigate the interrelation between the two events, and to investigate why the Solomon Islands have a historically high rate of doublet earthquakes. Teleseismic P waveform data for both events were used to obtain the slip distributions for the two earthquakes by a finite fault slip inversion method. The Mw 7.6 event is an east–west left-lateral strike slip, where the maximum slip is observed 8–24 km east of the hypocenter. The Mw 7.4 earthquake is a thrust event with north and south-dipping nodal planes. The fault plane is not clear from the aftershock distribution, but the north-dipping plane considered to be the likely fault plane because of the simpler slip distribution compared to the south-dipping plane. The static Coulomb failure stress changes caused by the first earthquake were calculated in the region of the second earthquake. The results show that there was a + 48.59 kPa change at the hypocenter for the assumed north-dipping plane and + 18.24 kPa for the assumed south-dipping plane of the Mw 7.4 event. The temporal pattern of aftershocks shows a possible rate increase of stress prior to the occurrence of the Mw 7.4 events, which may also contribute to the triggering of the second event by static Coulomb Stress changes. We propose a model that supports the geological complexity of the region that may encourage such doublet events. [ABSTRACT FROM AUTHOR]

The 2022 Mw6.2 Pasaman earthquake took place in central-west Sumatra in association with activity in the Sumatran Fault system. This study clarifies the spatial and temporal distribution of the Pasaman earthquake sequence and forecasts the earthquake sequence’s impact on the seismicity in the vicinity and in the Sumatran Fault system. We first examined the seismicity before the mainshock and observed temporal low b-value anomalies, shedding light on the earthquake’s precursor by monitoring b-values prior to the event. Based on the aftershocks in the first 18 days, we modeled the temporal distribution of the aftershocks according to the modified Omori’s law, which suggested this sequence could last 49–473 days. By further considering Båth’s law and the Gutenberg–Richter law, we estimated the temporal distribution of the maximum magnitudes in the aftershock sequence. To understand the spatial pattern of the aftershocks, we calculated the coseismic Coulomb stress change imparted by the Pasaman mainshock. Considering uncertainties of the Coulomb stress calculations from rupture geometry, mainshock parameters, friction coefficients, and strike angles of the receiver plane, the patterns of the Coulomb stress changes are similar that the stress increases extended northwest and southeast, consistent with aftershock distribution. We further evaluated rupture probability for each segment of the Sumatran Fault. Considering the stress perturbation imparted by the Pasaman earthquake, we expected a seismicity rate increase of ca. 40% at the Sumpur and Sianok segments in the short term. To quantify long-term rupture probability, the recurrence interval and the time elapsed since the previous earthquake were incorporated based on the time-dependent Brownian passage-time model. The earthquake probability at the Sumani segment in the coming 50 years was determined to be 72%. The results of this study have significant implications for subsequent probabilistic seismic hazard assessments, not only for Sumatra but also for certain metropolitan areas in Malaysia and Singapore. [ABSTRACT FROM AUTHOR]

The seismically active Sumatra subduction zone has generated some of the largest earthquakes in the instrumental record, and both historical accounts and paleogeodetic coral studies suggest these were large enough to transfer stress to the surrounding region, including the Great Sumatran Fault (GSF). Therefore, evaluating the stress transfer from these large subduction earthquakes could delineate segments of elevated stress along the GSF where large earthquakes may potentially occur. In this study, we investigated eight megathrust earthquakes from 1797 to 2010 and resolved the accumulated Coulomb stress changes onto 18 segments along the GSF. Additionally, we also estimated the rate of tectonic stress on the GSF segments which experienced large earthquakes. We considered two cases, with: (1) no forearc sliver movement, and (2) the forearc sliver movement suggested by recent studies. Based on the historical stress changes of large earthquakes and the increase in tectonic stress rate, we analyzed the time evolution of stress changes on the GSF. The Coulomb stress changes on the GSF due to megathrust earthquakes between 1797 and 1907 increased the Coulomb stress mainly on the southern part of GSF, which was followed by four major GSF events during 1890–1943. The estimation of tectonic stress rates using case (1) produces a low rate of stress accumulation and long recurrence intervals, which would imply that megathrust earthquakes play an important role in promoting the occurrence of GSF earthquakes. When implementing the arc-parallel sliver movement of case (2), the tectonic stress rates are much higher than case (1), with an observed slip rate of 15–16 mm/yr at the GSF consistent with a recurrence interval for full-segment rupture of 100–200 years. The case (2) result suggests that the occurrence of GSF earthquakes is dominantly controlled by the rapid arc-parallel forearc sliver motion. Furthermore, the analysis of the evolution of stress changes with time shows that some segments such as Tripa (North and South), Angkola, Musi and Manna, which have experienced full-segment rupture and are therefore likely locked, appear to have returned to stress levels similar to those prior to previous historical events, suggesting elevated earthquake hazard along these GSF segments. [ABSTRACT FROM AUTHOR]

The Türkiye-Syria earthquake doublet of 6 February 2023 (Mw 7.8 at 01:17 UTC and Mw 7.6 at 10:24 UTC) resulted in extensive damage and tens of thousands of casualties. We present the surface displacements of the two earthquakes from synthetic aperture radar (SAR) offset tracking measurements. We extracted the geometric parameters of the rupture faults from the surface displacements and early aftershock distribution, based on which we inverted the coseismic slip distributions. We then calculated Coulomb stress to investigate the triggering relationship between the earthquakes and stress transfer to neighbouring faults and regions. The coseismic ruptures of the earthquake doublet were predominantly left-lateral strike-slip motions distributed between 0 and 15 km depth. The maximum fault slip reached > 8 m (Mw 7.8) and almost 10 m (Mw 7.6). The coseismic deformation and fault slip motion are consistent with the overall westward extrusion of the Anatolian Plate relative to the Eurasian and Arabian plates. The Mw 7.8 earthquake increased Coulomb failure stress at the hypocenter of the Mw 7.6 earthquake, implying that the Mw 7.8 event had a strong positive causative effect. Moreover, coseismic stress perturbations revealed a positive Coulomb stress effect on the middle Puturge Fault, northern Dead Sea Fault Zone (DSFZ), Yesemek Fault, Antakya Fault, and Turkoglu Fault, indicating an increasing seismic hazard in these regions.

The Mw 6.3 Yutian earthquake, occurred in northwestern Tibet on 25 June 2020, is one of the major events sequentially occurring in the region following the 2008 Mw 7.2, 2012 Mw 6.2, and 2014 Mw 6.9 earthquakes, and is of great significance for studying the tectonic activity and assessing future seismic hazards in the region. In this study, we used Sentinel‐1 Synthetic Aperture Radar images to retrieve co‐ and post‐seismic deformation and to investigate the coseismic rupture behavior of the fault and the mechanisms of postseismic deformation. Based on the slip models of recent four nearby major earthquakes, we explored the local stress evolution, triggering mechanism of the 2020 event and future regional seismic hazards. Postseismic modeling reveals that afterslip on fault patches surrounding the ruptured co‐seismic patches is the main mechanism responsible for the near‐field deformation, with the poroelastic rebound relaxation only accounts for maximumly 25% of the ground displacement and limited impact on the overall deformation pattern. The Coulomb failure stress changes (ΔCFS) suggest that the 2020 Yutian earthquake was inhibited by the 2008 Mw 7.2 earthquake but facilitated by the 2012 Mw 6.2 and 2014 Mw 6.9 earthquakes, resulting in an overall ΔCFS with a large lateral gradient on the 2020 fault. Stress concentrations on nearby major faults indicate increasing chances of seismic hazards in the eastern section of the Altyn Tagh fault at 82.8°E, the western section of the Guozha Co fault at 81.5°E and the entire section of the Ashikule fault. Plain Language Summary: The 2020 Mw 6.3 Yutian earthquake is one of the major events sequentially occurred following the 2008 Mw 7.2, 2012 Mw 6.2, and 2014 Mw 6.9 earthquakes in Yutian County. As large earthquakes result in stress perturbations altering regional seismicity, it provides great opportunity for studying the regional tectonic activity and assessing future seismic hazards. In this study, we investigated the coseismic rupture behavior of the 2020 earthquake and the mechanisms of postseismic deformation observed by radar observations. We also explored the local stress evolution, triggering mechanism of the 2020 event and future seismic hazards. Postseismic modeling indicates that afterslip is responsible for most of the near‐field deformation, with the poroelastic rebound effect contributing only a small portion. Earthquakes prior to 2020 have generated considerable stress perturbations with complex patterns which may have triggered the 2020 Yutian earthquake. Stress concentrations on nearby faults indicate that future attention should be paid in the eastern section of the Altyn Tagh fault at 82.8°E, the western section of the Guozha Co fault at 81.5°E and the entire section of the Ashikule fault. Key Points: The afterslip and poroelastic rebound mechanisms were examined to explain the observed postseismic deformationPrevious major events caused complex stress changes on the fault ruptured in 2020 with along‐strike gradients from positive to negativeStress concentrations on major nearby faults were calculated and future seismic hazards were evaluated [ABSTRACT FROM AUTHOR]

Abstract The Mw 6.3 Yutian earthquake, occurred in northwestern Tibet on 25 June 2020, is one of the major events sequentially occurring in the region following the 2008 Mw 7.2, 2012 Mw 6.2, and 2014 Mw 6.9 earthquakes, and is of great significance for studying the tectonic activity and assessing future seismic hazards in the region. In this study, we used Sentinel‐1 Synthetic Aperture Radar images to retrieve co‐ and post‐seismic deformation and to investigate the coseismic rupture behavior of the fault and the mechanisms of postseismic deformation. Based on the slip models of recent four nearby major earthquakes, we explored the local stress evolution, triggering mechanism of the 2020 event and future regional seismic hazards. Postseismic modeling reveals that afterslip on fault patches surrounding the ruptured co‐seismic patches is the main mechanism responsible for the near‐field deformation, with the poroelastic rebound relaxation only accounts for maximumly 25% of the ground displacement and limited impact on the overall deformation pattern. The Coulomb failure stress changes (ΔCFS) suggest that the 2020 Yutian earthquake was inhibited by the 2008 Mw 7.2 earthquake but facilitated by the 2012 Mw 6.2 and 2014 Mw 6.9 earthquakes, resulting in an overall ΔCFS with a large lateral gradient on the 2020 fault. Stress concentrations on nearby major faults indicate increasing chances of seismic hazards in the eastern section of the Altyn Tagh fault at 82.8°E, the western section of the Guozha Co fault at 81.5°E and the entire section of the Ashikule fault.

On May 21, 2021, the M7.3 Maduo earthquake occurred within the Bayan Har Block, one of the most seismically active regions in the Tibetan Plateau. This aroused attention to the seismic hazards in this block. Understanding the stress transfer to adjacent faults is important for assessing seismic hazards. In this study, based on the elastic dislocation theory and a multi-layered lithospheric model, we calculate the Coulomb failure stress changes caused by this event on the adjacent major faults and identify the segments that experienced significant increases in stress. Our preliminary results show that five segments, including the middle segment of the Dari Fault, the Tuosuo Lake segment, the Maqin–Maqu segment, the western segment of the Dari Fault, and the Yushu segment of the Garze–Yushu Fault, experienced significant increases in co-seismic stress, which exceed the proposed threshold (1 ​× ​104 ​Pa) for triggering an earthquake. The stress change pattern associated with the post-seismic viscoelastic relaxation effect is substantially consistent with that caused by the co-seismic effect. The segments with high combined (co-plus post-seismic) stress changes are identical to those indicated by the co-seismic stress increase. Based on the stress change in this study and those of previous studies on seismic activity and fault stress evolution, we emphasize the seismic potential of the Maqin–Maqu segment, the Tuosuo Lake segment, and the middle-west segments of the Dari Fault, which should receive increased attention.

• The seismogenic fault is a typical sinistral strike-slip fault with a rupture length of over 160 km. • The displacement in E-W is the biggest among three-dimensional displacements with the RMSE 3.01 mm. • The peak slip is 5.53 m with the seismic moment of Mw 7.3 in the homogenous half-space model. • The peak slip is 5.96 m with the seismic moment of Mw 7.4 in the layered half-space model. On May 22, 2021, an Mw 7.4 earthquake occurred on the Maduo-Jiangcuo fault, located in Maduo County, Qinghai Province (China). According to the co-seismic deformation and the three-dimensional displacement reached from the interferometric synthetic aperture radar (InSAR) and the global navigation satellite system (GNSS), the rupture trace in the NWW direction was mapped, spanning a length of approximately 160 km and the earthquake happened on a typical sinistral strike-slip fault. In three-dimensional displacement, the displacement in E-W was bigger than that in N-S and vertical, with the RMSE 3.01 mm, 15.28 mm, and 5.16 mm respectively. Moreover, the slip distribution inverted with the homogeneous half-space model and layered half-space model, indicated that the corresponding magnitude was 7.3 Mw and 7.4 Mw, and the corresponding peak slip was 5.53 m and 5.96 m. The correlation coefficients of observed and predicted both exceeded 0.791, meeting the need for slip inversion. What is more, the peak inversion depth was no more than 15 km with strike angle and dip angle of 269° and 82.9° in the homogeneous half-space model and 265° and 83.7° in the layered half-space model, respectively. In addition, the Coulomb stress changes decreased on the Maduo-Jiangcuo fault and accumulated on the East Kunlun fault, which might cause aftershocks and future earthquakes were still possible. In short, the 2021 Mw7.4 Maduo earthquake made it possible to unravel seismic behavior in the Tibet plateau, which is of great significance for seismic hazard research. [ABSTRACT FROM AUTHOR]

Mankind has long been faced with natural destructive phenomena, including earthquakes. Awareness of the time and place of major earthquakes is essential to warn before occurring an earthquake in order to reduce human and financial losses. At present, it may not be possible to predict the exact time of future earthquakes, but to some extent, by studying the data of past earthquakes, high-risk areas with high seismic potential can be identified, and knowledge of these high-risk areas can reduce the damage caused by earthquakes in these regions. The study of stress changes in the earth's crust can be used to estimate the probability of an earthquake. Coulomb stress change analysis has been used in many seismic regions of the world. These studies show that in most cases, the location of subsequent earthquakes is affected by changes in the Coulomb stress caused by previous earthquakes in that region. In this study, in order to investigate the possible location of large earthquakes, Coulomb stress changes of 29 historical earthquakes and one instrumental earthquake magnitude greater than 5.5 in NW Iran were calculated. The study of mechanical interaction among earthquakes shows the spatial relationship between them in some events. For example, Coulomb stress change caused by the historical earthquake of 858 AD on the NTF, led to the rupture of its adjacent part in 1042 AD. The 1042 earthquake ruptured a large part of the NTF and increased the stress on the west side on the 1273 faulting plane. The next event in this sequence was the 1304 earthquake in the NTF, which was located at the region of the increase in the Coulomb stress caused by the previous earthquakes. The 1641 earthquake occurred in Dehkharqan region of Tabriz due to the increase in the stress of the fault system events in the NTF. In order to know about the areas that have highest probability, we compute the cumulative Coulomb stress change caused by the co-seismic deformation of earthquakes on strike-slip and dip-slip faults with optimal geometry. The results of these estimations show that the high-risk and probable areas for causing the next large earthquakes in the region Coulomb stress change increase due to previous earthquakes and have active faults in the direction of optimal strike-slip and dip-slip fractures. These areas for strike-slip faults are: the southeastern part of the NTF (Bostan-abad), the northern part of the faulting caused by the 1843 earthquake from the Maku fault and the southern part of the faulting caused by the 1840 earthquake. The areas for dip-slip faults are: Tasuj fault, between faultings caused by the earthquakes of 1807 and 1857, Mishu fault, the southern part of the faulting caused by the 1844 earthquake from Bozqush fault and the northern part of the faulting due to the 1879 earthquake from Bozghush fault. [ABSTRACT FROM AUTHOR]

The statistically point process model known as epidemic-type aftershock sequence (ETAS) model is employed for systematically investigating the seismic quiescence or seismic anomalies around the focal regions of large/strong earthquakes for NW Himalaya. For this propose, the model predicted the expected occurrence rates of earthquakes by estimating the model parameters from the earthquake occurrences times using maximum likelihood method, has been used. Then the exhibited relative quiescence due to decreasing occurrence rates from the modeled ones can be identified by inspecting the abnormally downward deviated plot from the extended cumulative curve of the Residual Point Process (RPP) events. Examination of such RPP events in the whole time interval exhibits significant 1.5 years and 2.0 years of relative seismic quiescence before the strong 1991 Uttarkashi (MW 6.8) and 1999 Chamoli (MW 6.6) earthquakes, respectively. Considering the optimally oriented planes of Uttarkashi earthquake, the Coulomb stress changes (ΔCFS) have been investigated to check the rate of seismicity around the focal region of Chamoli earthquake. It has been found that ΔCFS of Uttarkashi earthquake exhibits stress shadow in or near the source zone of Chamoli earthquake and eventually decreases seismicity rates due to seismic quiescence in the source zone. On the other hand, the detected quiescence and activation relative to the predicted seismicity rate are consistent with the obtained Coulomb stress to depict the associated anomalies being sensitive enough to detect a slight stress change in the study region. Henceforth, the increased or decreased seismic activity due to seismic activation or quiescence is found to be consistent with the patterns of the Coulomb's stress changes calculated on the ruptured fault planes of Uttarkashi earthquake. Hence, this ETAS model based on statistical technique can thus be incorporated with other sensitive geophysical instruments for identifying seismically quiet period not only in the seismic gaps, but also in its neighborhoods along the Himalayan range for mitigating seismic hazards due to impending great earthquakes. [ABSTRACT FROM AUTHOR]

To reveal the distribution pattern of aftershocks of the Mw 6.6 Lushan earthquake on April 20, 2013, we analyzed finite-source slip models from seismic waveform inversions and calculated the stress changes on and off the main rupture. In the spatial domain, the fitted coseismic slip–stress relation on subfaults is much closer to the quadratic stress drop model than to the uniform stress model. In the wavenumber domain, the slip and stress change spectrum decay asymptotically as k−3 and k−2, respectively, where k is the wavenumber. And in this domain, we also find that the prediction of a quadratic stress drop model matches data better than a uniform stress drop model. In addition, we studied the effective friction coefficient on the fault. Aftershocks were clustered around a relatively narrow zone that counters the main rupture plane. The narrow zone has a main rupture width with a standard deviation of 2.7 km for M ≥ 3 events. For 12 M ≥ 4.8 aftershocks, approximately 33% of nodal planes were calculated to be located in the zone of positive shear stress changes, while 83% were in the zone of positive normal stress changes (unclamp), suggesting a high effective friction coefficient μ ′ ≥ 0.8 on the main fault. Combined with the investigation in aftershocks triggered by blind thrust events at Whittier Narrows (USA), Zemmouri (Algeria), and Gorkha (Nepal), we suggest that the correlation between aftershocks and positive Coulomb stress changes increases with the effective friction coefficient μ ′ , and the effective friction coefficient and normal stress changes play an important role in aftershock triggering of blind thrust events. [ABSTRACT FROM AUTHOR]

A number of moderate earthquakes occurred in the South China continental edge or coastal area. Several large earthquakes are sparsely distributed along the seismic belt with the northeast direction between the South China and the continental shelf of the South China Sea. Coulomb stress changes of the 1969 Yangjiang main shock (Ms 6.4) with the following events of the 1986 ML 5.4, the 1987 ML 5.4 and the 2004 ML 5.2 in the Yangbian Bay area are studied. The complex stress patterns of the main shock caused by the dextral Pinggang strike-slip fault imported on the planes of the normal fault, strike-slip fault and thrust fault of three events indicate that the distribution of aftershocks mainly located in the areas of positive stress changes and part of aftershocks fall into the stress shadow area due to the reactivity of the local faults. The 1969 Yangjiang event occurred between the intraplate and the broad plate boundary zone setting when we apply on the empirical relationship between the aftershock durations and the fault-loading rate. The intersection fault model is proposed and could explain the stress changes of the Yangjiang earthquake sequences in South China coastal area. The future hazard assessment requires to take account of the stress increase area along the tip of the main shock source fault and off-fault stress increase area. [Display omitted] • Stress transfer and fault interactions show migration of the Yangjiang earthquake sequence. • The Yangjiang event occurred between the intraplate and the broad plate boundary zone setting. • The Coulomb stress changes of the mainshock indicate stress increase area for aftershocks. [ABSTRACT FROM AUTHOR]

On October 30, 2020, a strong earthquake (Mw6.6-7.0) occurred offshore, just north of Samos Island, causing life losses, injuries and damages, especially on the Turkish side. The broader area is characterized by a complex geodynamic setting with both rich seismic history and numerous active faults of different direction and kinematics. The first aim of this study is to define the seismic source of the mainshock, based on seismological and geodetic data (GPS measurements and originally processed GNSS records), as well as our field observations on Samos Island few days after the mainshock. The integration of this information leads to a N-dipping normal fault (Kaystrios fault) that controls the central-northern coast of Samos Island. We modelled the seismic source and calculated the theoretical dislocation (using the Okada formulae) on the surrounding GPS/GNSS stations, comparing it with the measured values. The results are very encouraging, especially on the station installed on Samos Island, giving confidence to our source model. We then used our seismic source to study the spatiotemporal evolution of the aftershock sequence by exploiting published seismological data (focal mechanisms and two seismic catalogues, one of which with relocated hypocentres) and our calculated Coulomb static stress changes caused by the mainshock. This comparison suggests that more faults than the Kaystrios fault were involved in the aftershock sequence. In order to investigate possible triggering and/or delay scenarios of the mainshock on nearby faults, the Coulomb stress changes are also studied showing various results according to each receiver fault. [ABSTRACT FROM AUTHOR]

The ENE striking Longmu Co fault and the North Altyn Tagh left-lateral slip fault have led to the complex regional structure in the northwestern Tibetan Plateau, resulting in a series of normal faulting and strike slip faulting earthquakes. Using both the ascending and descending Sentinel-1A/B radar images, we depict the coseismic deformation caused by the 2020 Yutian Mw 6.4 earthquake with a peak subsidence of ~ 20 cm. We determine the seismogenic fault geometry by applying the Bayesian approach with a Markov Chain Monte Carlo sampling method, which can better characterize the posterior probability density functions of the source model parameters. The estimation results reveal that the earthquake is a normal faulting event with a moderate strike slip component. Based on the optimal fault geometry model, we extend the fault plane and invert for the distributed coseismic slip model. The optimal slip model shows that the coseismic slip is mainly concentrated at shallow depths of 3–10 km with a maximum slip of ~ 1.0 m. Our preferred geodetic coseismic model exhibits no surface rupture, which may likely be due to the shallow slip deficit in the uppermost crust. We calculate the combined loading effect of the Coulomb failure stress changes induced by the coseismic dislocations and postseismic viscoelastic relaxation of the 2008 Mw 7.1, 2012 Mw 6.4 and 2014 Mw 6.9 Yutian events. Our study demonstrates that the three preceding major Yutian shocks were insufficient to trigger the 2020 Yutian earthquake, which we consider perhaps reflects the natural release of elastic strain accumulated mainly through localized tectonic movement. We attribute the 2020 Yutian event to the release of extensional stress in a stepover zone controlled by the Longmu Co and the North Altyn Tagh sinistral strike slip fault systems. The seismic risk in the southwest end of the North Altyn Tagh fault has been elevated by the Yutian earthquake sequences, which require future attention. [ABSTRACT FROM AUTHOR]

From November 2012 to May 2013, the coastal region of Bejaia (northeastern Algeria), experienced three distinct seismic sequences in about 6 months. The first one was on 28 November 2012 started with a mainshock of magnitude Mw = 5.1, and the second one occurred on 22 February 2013, a few kilometers southeast from the first one and culminated with a magnitude Mw = 4.3 earthquake. The last sequence comprised two shocks of moderate magnitude: a Mw 5.2 event on 19 May 2013, followed by a Mw 5.0 event on 26 May. Earthquakes were relocated using the double-difference method with differential times derived from phase-picked data and waveform cross-correlation delays. We compiled a dataset of 252 accurately relocated events that are associated with focal mechanism solutions consistent with a near-vertical, right-lateral strike-slip fault striking NW–SE. The data analysis is coherent with a new fault extending over 35 km from the Gulf of Bejaia to the northeast of Kherrata. This newly discovered active fault, we name it the Babors Transverse Fault, appears to be segmented in four segments (S1–S4) evidenced by separate earthquake clusters. Static Coulomb stress changes and the spatiotemporal evolution of seismicity suggest static stress triggering, with the rupture first activated in the S1 segment in the northwest, migrating to S2, and terminating in S3 and S4 in the southeast. Stress tensor inversion from focal mechanisms implies that the dominant local stress field is a pure strike-slip regime, with N–S maximum horizontal compression in good agreement with the velocity field displaying reorientation compared to the oblique convergence of Africa–Eurasia. In this study, the newly identified Babors Transverse and Tizi N'Berber–Darguinah faults, in association with the NNW–SSE offshore active fault of the Greater Kabylian block (in the north) and the NNW–SSE right-lateral strike-slip Lâalam fault (in the south), form an en echelon fault system that acts as a transfer zone between offshore thrust faulting and the Ghardimaou–North Constantine strike-slip fault. [ABSTRACT FROM AUTHOR]

Based on the elastic spherical Earth models, this study presents the radial Love numbers and Green's functions of the surface load problem, then evaluates the effect of different Earth models on the Coulomb stress changes due to elastic deformation by surface load. First of all, the radial load Love numbers are introduced and verified by comparing them with the results of an analytical method. Second, the formulae of the radial Green's functions of the internal displacements and strain tensors are obtained by summing the Love numbers. The results are compared with Green's function of half-space to verify the correctness. Then, the stress tensors are obtained by the constitutive relation. Finally, the Coulomb stress changes due to elastic deformation around the Wenchuan Mw7.9 earthquake by the impoundment load of the Zipingpu reservoir are calculated based on five Earth models. The results show that the elastic deformations caused by the impoundment load do not increase the seismicity rate in the study area. At the epicenter of the great event, the maximum effect due to the Earth models is about 38%. The stratification of the Earth is the main effect factor on the Coulomb stress change, and it should not be ignored in actual studies. The biggest difference of Coulomb stress changes based on the different stratified Earth models is close to 15%, which also cannot be ignored. [ABSTRACT FROM AUTHOR]

Dynamic triggering of large, detectable slow slip events (SSEs) is rarely observed, even though regional earthquakes often trigger tectonic tremors and very low frequency earthquakes. In this study, we investigate stress sensitivity of dynamic triggering of shallow SSEs in the Nankai Trough offshore of Kii Peninsula, Japan. We first identify additional shallow SSEs that have not been reported in previous studies and obtain a 15‐year‐long catalog of SSEs, some of which are triggered by passing seismic waves originating from large regional earthquakes. We then quantify dynamic and static stress perturbations on the plate interface induced by 19 candidate regional earthquakes using numerical simulations of seismic wave propagation. We find that SSE propensity to dynamic triggering depends mainly on the maximum Coulomb stress change and that relatively large dynamic stresses (>10–20 kPa) are needed to trigger a shallow SSE in the Nankai Trough. Regional earthquakes that can induce such large amplitude of dynamic stresses on the plate interface are relatively rare, which might explain the scarcity of dynamic triggering of large, detectable SSEs along the Nankai as well as other subduction zones. In addition, our analysis suggests that intraslab earthquakes can efficiently trigger SSEs in subduction zones via less‐attenuated, slab‐guided waves. Moreover, our results support the idea that an accretionary wedge in subduction zones promotes the dynamic triggering of shallow SSEs. Key Points: We identify additional shallow slow slip events (SSEs) in the Nankai Trough that were not previously reportedStress perturbations resulting from 19 large earthquakes are computed and compared against the timing of shallow SSEsThe propensity for SSE triggering mainly depends on the maximum dynamic stress change [ABSTRACT FROM AUTHOR]

The present east–west crustal extension of the Tibetan Plateau has been demonstrated through field investigations, satellite imagery, geodetic deformation, and earthquake focal mechanisms. Normal faulting earthquakes in the interior Tibetan Plateau are almost entirely confined to regions at elevations over 4000 m. However, our knowledge of the eastward extent of normal faulting in the plateau is still uncertain due to the limited occurrence of well-documented earthquakes. Based on a retrospective analysis of the 2016 Mw 5.9 Zaduo earthquake in the Tibetan Plateau, we consider the NE trending Zaduo-Shanglaxiu fault as the most likely rupture fault through a comprehensive analysis of relocated aftershock sequences, mapped active faults, and newly acquired strain rate tensor. We further determine seismogenic fault geometry using a Bayesian approach and sample with a Markov Chain Monte Carlo method. We interpret the Zaduo earthquake to reflect the release of slowly accumulated elastic strain accumulated mainly by gravitational forces rather than a delay triggering event from the 2010 Yushu earthquake. The viscoelastic calculations to estimate Coulomb stress changes over time indicate that long-term viscous flow in a weak mid-crust can load adjacent faults far more than static stress changes alone. Our results show that the Zaduo earthquake was a Mw 5.9 oblique normal faulting event that occurred in the easternmost part of the Tibetan Plateau, suggesting that the Qiangtang block at longitude ~ 95° E accommodates east–west extensional crustal deformation by small-scale oblique normal faults, which may act as the boundary of micro-blocks. This may also mean that the normal faulting in the Qiangtang block is expanding outwards, and a new rifting system may be formed, which requires more geological evidence. [ABSTRACT FROM AUTHOR]

Fault models are quickly produced and iteratively improved over weeks to years following a major earthquake, to characterise the dynamics of rupture, evaluate the role of stress transfer, and contribute to earthquake forecasting. We model Coulomb stress transfer (ΔCFS) between the largest foreshock (Mw 5.4; 1 year prior to first mainshock) and three Mw 6.1 to 6.5 earthquakes that occurred in a 12-hour period on January 22, 1988 in central Australia (Tennant Creek earthquake sequence) to investigate the role of static stress transfer in earthquake triggering relative to progressive source model development. The effects of fault model variance are studied using ΔCFS modelling of five different fault source model sequences (27 total models) using different inputs from seismic and geospatial data. Some initial models do not yield positive ΔCFS changes proximal to hypocentres but in all models, preceding earthquakes generate positive ΔCFS (≥0.1 bar) on ≥10 to 30% of the forthcoming receiver fault rupture areas. The most refined and data-integrative model reveals ΔCFS ≥ +0.7 to +13 bars within 2 km of impending hypocentres and large (≥30 to 99%) areas of positive ΔCFS. When compared to global compilations of threshold ΔCFS prior to impending ruptures (average = 3.71 bar, median = 1 bar), this suggests that Coulomb stress change theory adequately explains the Tennant Creek rupture sequence. In the most-refined model, earthquake inter-event times decrease as ΔCFS increases, suggesting that higher stress magnitudes may have more rapidly (within hours) triggered successive events, thus accounting for some temporal aspects of this sequence. ΔCFS analyses provide a useful framework for understanding the spatiotemporal aspects of some intraplate earthquakes. The progressive refinement of source models using emergent data may reduce epistemic uncertainties in the role of stress transfer that result from different model inputs, approaches, and results. • Coulomb stress modelling has been used to investigate the rupture behaviour of the 1987 to 1988 Tennant Creek earthquake sequence in Australia. • Coulomb stress triggering explains the sequence evolution for most of the fault sequence models. • Increases in knowledge of source models may increase confidence in attributing spatiotemporal patterns of earthquakes to stress changes. [ABSTRACT FROM AUTHOR]

Historical accounts and geological surveys suggest that a sequential rupture event occurred in 1596 CE in the Median Tectonic Line fault zone (MTLFZ) in southwestern Japan. During this event, known as the 1596 Keicho earthquake, the rupture probably propagated in two or three sequential stages, similar to a series of events that occurred along the North Anatolian fault during 1939–1999. The detailed rupture process of the 1596 earthquake event is unknown, however, because coseismic seismological, geological, and geodetic observation data are not available. To reconstruct the rupture processes, we integrated data from Coulomb stress change analyses, fault geometrical analyses, historical accounts, and rupture history. The results suggest that the rupture initiated on the Kawakami fault on 1 September 1596 and propagated bilaterally, to the Beppu Bay fault system, which ruptured on 4 September, and to the MTLFZ in eastern Shikoku and the Rokko‐Awaji fault zone and Arima‐Takatsuki Tectonic Line in the Kinki area, which ruptured on 5 September. However, there is a small possibility that the rupture initiated at the western end of the MTLFZ and propagated eastward unilaterally. The propagation of ruptures might be sensitively controlled not only by stress perturbation and fault geometry but also by rupture history. Evaluation of fault rupture behavior from various viewpoints can contribute to the mitigation of future seismic disasters in fault zones where detailed coseismic observation data from the past are lacking. Key Points: Coulomb stress change analyses might provide important information to estimate the rupture scenario of a historical rupture eventFault rupture history regional stress conditions and fault geometry might contribute to triggering rupture of neighboring faultsOur results indicate that the 1596 Keicho earthquake likely initiated on the Kawakami fault and that the rupture propagated bilaterally [ABSTRACT FROM AUTHOR]

Continental rifting evolves through repeated tectonic and magmatic processes. Here we investigate the 2007–2008 northern Tanzania rifting episode to understand the interactions between magmatism and border fault slip during immature continental rifting. We compare modeled stress changes with geodetic observations from the western adjacent border fault of the Natron basin. We model six distinct phases of the rifting episode, including the eruptive activity of Ol Doinyo Lengai. The southern portion of the border fault experienced a positive cumulative Coulomb stress change, consistent with newly processed Global Positioning System data showing a distinct instance of slip during this time period. Our work suggests active volcanism and faulting are correlated in time, indicating magmatism associated with volcanic activity influences slip on border faults in immature continental rifts. Key Points: Magmatically induced stress perturbations have the potential to trigger fault slip on rift border faultsMagmatic events have the potential to trigger strike‐slip motions on a rift border faultThe proximity of magmatic activity may affect occurrences of slip on adjacent border faults [ABSTRACT FROM AUTHOR]

Abstract The Mw6.9 Yushu earthquake occurred on 14 April 2010, in Qinghai, China; the largest aftershock, a Mw5.8 event, occurred west of the mainshock on 29 May 2010 (˜40 days later). The aftershock had a different focal mechanism from the mainshock. Furthermore, seismicity after 29 May showed different spatial characteristics in terms of focal depth and distribution direction. To better understand the faulting and the relationship between these two events, we derived the whole displacement field caused by the Yushu mainshock and the Mw5.8 aftershock based on multi-perspective Interferometric Synthetic Aperture Radar (InSAR) data. We then conducted a robust inversion of the slip distribution jointly constrained by InSAR and GPS data. The results indicate that the Mw5.8 aftershock produced a separated deformation field with significant displacement changes of up to ˜4–6 cm, which indicates another intersecting ruptured fault at the west end of the Yushu fault. The slip distribution shows a 75-km NW rupture with a maximum slip of ˜2.1 m at a depth of ˜0–10 km on the main Yushu fault, and a 20 km NE rupture with peak slip of ˜0.4 m at a depth of ˜5–15 km on a vertical hidden fault. Both events showed a dominant left-lateral component. The total rupture length associated with the 2010 Yushu earthquake sequence reached ˜95 km. By calculating Coulomb stress changes, we confirmed that the mainshock triggered the Mw5.8 aftershock. Our results imply that the increased stress at the western end of the Yushu fault caused by the mainshock rupture may have played an important role in transferring the rupture plane from the Yushu fault to the NE hidden fault. [ABSTRACT FROM AUTHOR]

Aftershock sequences are an ideal testing ground for operational earthquake forecasting models as they contain relatively large numbers of earthquakes clustered in time and space. To date, most successful forecast models have been statistical, building on empirical observations of aftershock decay with time and earthquake size frequency distributions. Another approach is to include Coulomb stress changes from the mainshock which influence the spatial location of the aftershocks although these models have generally not performed as well as the statistical ones. Here we develop a new hybrid Epidemic‐Type Aftershock Sequence (ETAS)/Coulomb model which attempts to overcome the limitations of its predecessors by redistributing forecast rate from negatively to positively stressed regions based on observations in the model learning period of the percentage of events occurring in those positively stressed regions. We test this model against the 1992 Landers aftershock sequence using three different ETAS kernels and five different models for slip in the Landers earthquake. We also consider two variations of rate redistribution, one based on a fixed value and the other variable depending on the percentage of aftershocks observed in positively stressed Coulomb regions during the learning period. We find that the latter model performs at least as well as ETAS on its own in all tests and better than ETAS in 14 of 15 tests in which we forecast successive 24‐hr periods. Our results suggest that including Coulomb stress changes can improve operational earthquake forecasting models. Key Points: We propose a new hybrid model based on the ETAS model and Coulomb stress informationWe test this model on the 1992 Landers earthquake sequenceWe show an improvement of the results using this hybrid model compared to the classical ETAS model [ABSTRACT FROM AUTHOR]

Abstract After M W 7.8 Nepal earthquake occurred, the rearrangement of stresses in the crust commonly leads to subsequent damaging earthquakes. We present the calculations of the coseismic stress changes that resulted from the 25th April event using models of regional faults designed according to south Tibet-Nepal structure, and show that some indicative significant stress increases. We calculate static stress changes caused by the displacement of a fault on which dislocations happen and an earthquake occurs. A M W 7.3 earthquake broke on 12 May at a distance of ~ 130 km SEE of the M W 7.8 earthquake, whose focus roughly located on high Coulomb stress change (CSC) site. Aftershocks (first 15 days after the mainshock) are associated with stress increase zone caused by the main rupture. We set receiver faults with specified strikes, dips, and rakes, on which the stresses imparted by the source fault are resolved. Four group normal faults to the north of the Nepal earthquake seismogenic fault were set as receiver faults and variant results followed. We provide a discussion on Coulomb stress transfer for the seismogenic fault, which is useful to identify potential future rupture zones.

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An intraplate earthquake doublet, with 11-min delay between the events, devastated the city of Varzeghan in northwestern Iran on August 11, 2012. The first Mw 6.5 strike-slip earthquake, which occurred after more than 200 years of low seismicity, was followed by an Mw 6.4 oblique thrust event at an epicentral separation of about 6 km. While the first event can be associated with a distinct surface rupture, the absence of a surface fault trace and no clear aftershock signature makes it challenging to identify the fault plane of the second event. We use teleseismic body wave inversion to deduce the slip distribution in the first event. Using both P and SH waves stabilize the inversion and we further constrain the result with the surface rupture extent and the aftershock distribution. The obtained slip pattern shows two distinct slip patches with dissimilar slip directions where aftershocks avoid high-slip areas. Using the estimated slip for the first event, we calculate the induced Coulomb stress change on the nodal planes of the second event and find a preference for higher Coulomb stress on the N-S nodal plane. Assuming a simple slip model for the second event, we estimate the combined Coulomb stress changes from the two events on the focal planes of the largest aftershocks. We find that 90% of the aftershocks show increased Coulomb stress on one of their nodal planes when the N-S plane of the second event is assumed to be the correct fault plane. [ABSTRACT FROM AUTHOR]

By using slip model from USGS and focal mechanism and aftershocks distribution from Iranian Seismological Center (IRSC) for Sarpol-e Zahab earthquake (Mw 7.3) on November 12, 2017, we investigated the correlation between Coulomb stress changes and aftershocks distribution. In this study, about 500 aftershocks with magnitude larger than 2.5 and azimuthal gap less than 180 degrees were selected. Calculated Coulomb stress changes on the optimally oriented faults showed that most of the seismicity occurred in regions of increased stress and the majority of them concentrated on the ruptured plane, especially in west and south parts. Besides, nodal planes of the selected 11 aftershocks received positive Coulomb stress changes. Therefore, there is a good correlation between Coulomb stress changes and aftershocks distribution in Sarpol-e Zahab event. Furthermore, calculated static stress on the surrounding faults showed that middle part of the High Zagros Fault (HZF), the northern part of the Main Recent Fault (MRF), and the northern part of the Zagros Foredeep Fault (ZFF) are located in the positive stress change area. [ABSTRACT FROM AUTHOR]

In this paper, the relationship between the dike-forming magmatic intrusions and the faulting process at Mount Etna is investigated in terms of Coulomb stress changes. As case study, a complete time-dependent 3-D finite element model for the 2002–2003 eruption at Mount Etna is presented. In the model, which takes into account the topography, medium heterogeneities and principal fault systems in a viscoelastic/plastic rheology, we sequentially activated three dike-forming processes and looked at the induced temporal evolution of the Coulomb stress changes, during the co-intrusive and post-intrusive periods, on Pernicana and Santa Venerina faults. We investigated where and when fault slips were encouraged or not, and consequently how earthquakes may have been triggered. Results show positive Coulomb stress changes for the Pernicana Fault in accordance to the time, location and depth of the 27 th October 2002 Pernicana earthquake (M d = 3.5). The amount of Coulomb stress changes in the area of Santa Venerina Fault, as induced by dike-forming intrusions only, is instead almost negligible and, probably, not sufficient to trigger the 29 th October Santa Venerina earthquake (M d = 4.4), occurred two days after the start of the eruption. The necessary Coulomb stress change value to trigger this earthquake is instead reached if we consider it as induced by the 27 th October Pernicana biggest earthquake, combined with the dike-induced stresses. [ABSTRACT FROM AUTHOR]

We conducted a systematic detection of micro-seismicity in Southern Tibet 1.6 days before and 4.4 days after the 2015 Mw 7.8 Gorkha, Nepal earthquake. Our study employs 368 template events listed in the China Earthquake Networks Center (CENC) catalog. With the waveform-based matched filter technique, we detected five times more earthquakes than listed in the CENC catalog during our study period. The seismicity in Southern Tibet shows a significant increase immediately following the Gorkha, Nepal earthquake, including two normal-faulting events (the Mw 5.8 Tingri and Mw 5.3 Nyalam earthquakes) about 3 and 11 h after the mainshock, respectively. Although the static stress changes ΔCFS showed a slightly better correlation with the seismicity rate changes than the peak dynamic stress changes ΔCFS( t ), the absolute value of the static stress change at the epicenter region of the Mw 5.8 Tingri earthquake is ~ 10 kPa, roughly two orders smaller than the peak dynamic stress change of 2.2 MPa. Although we are unable to identify the primary triggering mechanism, it is evident that the 2015 Nepal earthquake triggered widespread seismicity in Southern Tibet. Our results highlight the potential increase of seismic hazard in Southern Tibet due to the occurrence of major thrust earthquakes along the Himalaya frontal thrust faults. [ABSTRACT FROM AUTHOR]

During the first days of December 2015, there were four paroxysmal events at the “Voragine” crater on Mount Etna, which were among the most violent observed during the last two decades. A few days after the “Voragine” paroxysms, the Pernicana – Provenzana fault system, located near the crater area, underwent an intense seismic swarm with a maximum “local” magnitude M L of 3.6. This paper investigates the relationship between the eruptive phenomenon and the faulting process in terms of Coulomb stress changes. The recorded seismicity is compatible with a multicausal stress redistribution inside the volcano edifice, occurring after the four paroxysmal episodes that interrupted the usual trend of inflation observed at Mt. Etna. The recorded seismicity falls within the framework of a complex chain of various and intercorrelated processes that started with the inflation preparing the “Voragine” magmatic activity. This was followed with the rapid deflation of the volcano edifice during the paroxysmal episodes. We determined that the recorded deflation was not the direct cause of the seismic swarm. In fact, the associated Coulomb stress change, in the area of seismic swarm, was of about −1 [bar]. Instead, the fast deflation caused the rarely observed inversion of dislocation in the eastern flank at the same time as intense hydrothermal activity that, consequently, underwent an alteration. This process probably reduced the friction along the fault system. Then, the new phase of inflation, observed at the end of the magmatic activity, triggered the faulting processes. [ABSTRACT FROM AUTHOR]

The Great Himalayan earthquakes are believed to originate on the Main Himalayan Thrust, and their ruptures lead to deformation along the Main Frontal Thrust (MFT). The rupture of the April 25, 2015 (Mw 7.8), earthquake was east-directed, with no part relayed to the MFT. The aftershock distribution, coseismic elevation change of ~1 m inferred from the InSAR image, and the spatial correspondence of the subtle surface deformations with PT, a previously mapped out-of-sequence thrust, lead us to explore the role of structural heterogeneities in constraining the rupture progression. We used teleseismic moment inversion of P- and SH-waves, and Coulomb static stress changes to map the slip distribution, and growth of aftershock area, to understand their relation to the thrust systems. Most of the aftershocks were sourced outside the stress shadows (slip >1.65 m) of the April 25 earthquake. The May 12 (Mw 7.3) earthquake that sourced on a contiguous patch coincides with regions of increased stress change and therefore is the first known post-instrumentation example of a late, distant, and large triggered aftershock associated with any large earthquake in the Nepal Himalaya. The present study relates the slip, aftershock productivity, and triggering of unbroken stress barriers, to potential out-of-sequence thrusts, and suggests the role of stress transfer in generating large/great earthquakes. [ABSTRACT FROM AUTHOR]

We test the static Coulomb stress triggering hypothesis for three recent megathrust earthquakes (the 2004 Sumatra-Andaman earthquake, the 2010 Maule earthquake, and the 2011 Tohoku-Oki earthquake) using focal mechanism solutions for actual earthquakes as receiver faults to calculate Coulomb stress changes. For the 2004 Sumatra-Andaman and 2011 Tohoku-Oki earthquakes, the median values of the Coulomb stress changes for 100 consecutive earthquakes revealed temporal changes from approximately zero before the megathrust earthquake to significant positive values following the mainshock, followed by decay over time. Furthermore, the ratio of the number of positively to negatively stressed receiver faults increased after the megathrust. These results support the triggering hypothesis that the static stress changes imparted by megathrust earthquakes cause seismicity changes. This is in contrast to the results of a previous study that used optimally orientated receiver faults to calculate Coulomb stress changes, and this difference indicates the importance of considering the spatial and temporal heterogeneities of receiver fault distributions. For the 2010 Maule earthquake, however, the results are strongly dependent on fault-slip models. Since most receiver faults are concentrated in the mainshock source region, slip models significantly affect the computed Coulomb stress changes and sometimes cause anomalous stress concentrations along the edge of each sub-fault. [ABSTRACT FROM AUTHOR]

The North Sulawesi subduction zone (NSSZ) was ruptured by a series of large earthquakes (M w >7) since 1990s, generally triggered small to moderate tsunamis in the surrounding seas and ocean. But the 2018 Sulawesi M w 7.5 earthquake ruptured the west subduction zone and induced a large tsunami that displaced hundreds of people. These large earthquakes, especially the deeper thrust events, generated stress loading to the shallow megathrust that could rupture to excite exceptional tsunami hazard as observed in Sumatra, Japan and the other subduction zones. Whether the stress loading from downdip events can trigger future failure of a shallow tsunami earthquake and its ensuring tsunami hazard impact remains elusive. Here we investigate the potential of earthquake and tsunami by analyzing the historical earthquake characteristics, calculating Coulomb stress changes and simulating hundreds of hypothetical earthquake ruptures to assess the plausible tsunami hazard in the NSSZ. Our results show that a series of M w 7+ downdip megathrust earthquakes have loaded most of the megathrust, especially the shallow portion (<10 km), with increased stress >10 kPa, implicating a high potential of future large earthquakes and ensuring outsize tsunamis. Our modeled tsunami wave heights vary between >0 and 43 m along the North Sulawesi coastlines. One intriguing fact is that the end point of the tsunami wave energy dissipation path gains a comparable tsunami impact as the region in the rupture zone for all the magnitude considered, highlighting a dual-pattern threatened regions in the Celebes Sea. Importantly, the thrust and fold belt structure in the wide outer wedge of the accretionary prism and the strong seafloor bathymetry variation offshore Sulawesi Island could serve an efficient wave-amplification tool that need to be considered in future hazard assessment. Our findings alert that the earthquake and tsunami hazard potential are largely raised by these downdip major earthquakes. • A series of M w 7+ downdip earthquakes loaded the most shallow part of the NSSZ with Coulomb stress changes >10 kPa. • The fault structure of the frontal accretionary prism and the strong offshore depth changes could largely amplify tsunami waves. • The earthquake and tsunami hazard potential at the NSSZ are raised after these major earthquakes. [ABSTRACT FROM AUTHOR]

Tien Shan tectonic belt has experienced intense seismicity and a series of destructive strong earthquakes. However, earthquake triggering effects and faulting interactions in this area are poorly understood. A 3D finite element model of Tien Shan tectonic belt is constructed, to investigate stress evolutions on major faulting zones driven by interseismic tectonic loading and historical strong earthquakes with M≥ 6.0 since 1900. The numerical results show Tien Shan is dominated by nearly N-S compression, with higher tectonic loading rate in southwest Tien Shan. 1906 Manas M7.7 earthquake exerted pronounced Coulomb stress increase on its adjacent faulting zones, especially in the epicenter of 2016 Hutubi M6.0 earthquake. And three large earthquakes with M≥ 8.0, e.g., Chilik M8.3 earthquake in 1889, Kemin M8.0 earthquake in 1911 and Atushi M8.2 earthquake in 1902, increased the Coulomb stress by above 100 kPa in the epicenter of 1991 Keping M6.0 earthquake. While, stress perturbations by other strong earthquakes are limited, with slight Coulomb stress changes in the epicenters of their subsequent earthquakes. Overall, strong earthquakes with M> 7.0 in Tien Shan, induced substantial Coulomb stress changes on the adjacent faulting zones. Stress evolutions on major faults reveal higher stress accumulation in southwest Tien Shan, east KQX fault, west BoA fault, and HMT fault, indicating higher seismic risk. [Display omitted] • Tectonic loading rate is higher in southwest Tien Shan, and decreases eastward. • 1906 Manas M7.7 earthquake significantly promoted 2016 Hutubi M6.0 earthquake. • Faults in southwest Tien Shan were greatly affected by M≥ 8.0 earthquakes nearby. • Higher crustal stress in southwest Tien Shan, east KQX, west BoA and HMT faults. [ABSTRACT FROM AUTHOR]

Six alternative models of slip distribution during the 1906 Esmeraldas (Mw = 8.8) megathrust earthquake are used to compute Coulomb stress changes on two types of specific faults and onto optimal strike-slipe faults along the Colombia-Ecuador Pacific region. Coulomb stress changes are in the range −0.5–0.5 MPa projected on specific faults varies spatially depending on target fault configuration (dip and sense of motion): Slip along low-angle reverse faults would be inhibited whereas slip along near-vertical strike-slip faults would be facilitated in the southern rupture region and inhibited in the northern rupture region. The patterns of Coulomb stress changes on optimal strike-slip faults located on the landward side of the 1906 rupture is not strongly dependent on the regional stress tensor, suggests that motion along many faults and fault segments might be facilitated, and exhibits good spatial correlation with shallow seismicity. The modelled 1906 Esmeraldas rupture is compared to the recent 2010 Mw = 8.8 Maule, Chile earthquake and the results may aid in improving current hazard estimates and degree of preparedness in the Colombia-Ecuador Pacific region. [ABSTRACT FROM AUTHOR]