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The Shanxi Graben is a transitional zone between the Ordos Block and North China Plain with complex structures and frequent earthquakes. Six earthquakes with M ≥ 7.0 have been recorded in the area, including the 1303 Hongtong M 8 and 1695 Linfen M 7.8 earthquakes in the Linfen Basin. Research on these two large earthquakes, closely related in time and space, is lacking. Our objective was to use deep seismic reflection profiles and 3D velocity structure data from previous research, along with seismological observation results, to interpret the geological structure near the source of the two earthquakes. A 3D geometric model of the seismogenic fault was constructed, and the relationships among the deep and shallow structures, deep seismogenic environment, and two large earthquakes were explored. Differences in seismogenic environment between the southern and northern Linfen Basin were identified. The distribution of small earthquakes in the southern Linfen Basin was scattered, and the overall distribution was at depths <25 km. The small earthquakes in the northern part of the basin were dense and concentrated at depths of 25–35 km. Low-velocity layers at an approximate depth of 15–20 km in the southern basin led to differences in seismogenesis between the two regions. Based on the area of the 3D geometric model of the Huoshan Fault, the maximum magnitude of an earthquake caused by fault rupture is Mw 7.7, so the magnitude of the 1303 Hongtong earthquake might be overestimated. Numerical simulation results of Coulomb stress showed that the 1303 Hongtong earthquake had a stress-loading effect on the 1695 Linfen earthquake. The change in Coulomb rupture stress was 1.008–2.543 bar, which is higher than the generally considered earthquake trigger threshold (0.1 bar). We created a new 3D source model of large earthquakes in the Linfen Basin, Shanxi Province, providing a reference and typical cases for risk assessment of large earthquakes in different regions of the Shanxi Graben. [ABSTRACT FROM AUTHOR]

Between September 17 and 18, 2022, a series of earthquakes struck the southern Longitudinal Valley of Taiwan, causing severe damage to infrastructure, particularly bridges, railroads, buildings, and highways in Taitung and Hualien. The primary event in this sequence was the Chihshang earthquake, measuring magnitude of M L 6.9, preceded by a significant foreshock of M L 6.4 the day before. Notably, the highest intensity reported in the epicentral region during this earthquake sequence reached 6 + , marking the highest intensity ever recorded since the Central Weather Bureau (CWB) revised its seismic intensity scale. In this study, we examined the strong ground motion data recorded by the low-cost P-alert network to investigate the cause of structural damage to buildings, railway stations, schools, and other structures in the affected area. Our analysis encompassed data from a total of 17 monitoring stations. The observed peak ground acceleration (PGA) ranges from 0.06 g and 0.78 g, the peak spectral acceleration or response spectrum (PSA) spanned from 0.20 g at 0.50 s to 3.87 g at 0.41 s, and site amplification varied from 4 at 0.6 Hz to 12.6 at 5.2 Hz. The reported damage of single storey house at Taitung City is correlated with the higher amplification 4.5 at 0.14 s; Bridge and factory at Chihshang Township is correlated with the higher amplification 5 at 0.17 s; Railway station at Zhuoxi Township with the higher amplification 7.5 at 0.3 s; of three storey building at Yuli Township with amplification 8 at 0.26 s and, also higher PSA 2.83 g at 0.29 s, and several schools at Kaoshiung City with amplification 7.2 at 0.37 s and with high PSA 3.87 g at 0.41 s. Additionally, we studied the static Coulomb stress changes resulting from the coseismic slip of the main shock, which contributed to an increase in aftershock occurrences. The occurrence of a high-intensity earthquake ( M L 6.9) on September 18, 2022, within a region of positive Coulomb stress changes, provides support for the hypothesis of aftershock triggering. Through analysis, we found that stronger foreshock ( M L 6.4) occurred in the rupture area of mainshock foreshock, positioned adjacent to the main fault. [ABSTRACT FROM AUTHOR]

During the drilling process, the issue of drilling fluid loss can lead to changes in the mechanical properties of the formation, thereby altering the stress environment of nearby faults. In order to assess the risk of fault activation during drilling operations, the Ordos M area shale was selected as the research object. Mechanical experiments were conducted on rock samples immersed in water-based drilling fluid with a pressure differential of 2 MPa and a temperature of 50 °C. The changes in the mechanical properties of the shale before and after immersion in drilling fluid were determined. Based on the experimental results, combined with the spring combination model and fault activation theory, a quantitative evaluation of fault activation risk was conducted. The findings revealed that the shale in this region has a high clay content, demonstrating a certain level of water sensitivity. The presence of micro-pores and micro-fractures is well-developed, increasing the interaction probability between drilling fluids and clay minerals. After immersion in drilling fluid, there was a varied decline in all mechanical strengths of the shale. The elastic modulus is positively correlated with the shear strength and Coulomb stress of the fault plane. The Poisson's ratio is positively correlated with the shear strength and negatively correlated with the Coulomb stress. The greater the internal friction and cohesion, the higher the shear strength of the fault plane, and the larger the friction coefficient, the smaller the Coulomb stress, resulting in a more stable fault. [ABSTRACT FROM AUTHOR]

Abstract During the drilling process, the issue of drilling fluid loss can lead to changes in the mechanical properties of the formation, thereby altering the stress environment of nearby faults. In order to assess the risk of fault activation during drilling operations, the Ordos M area shale was selected as the research object. Mechanical experiments were conducted on rock samples immersed in water-based drilling fluid with a pressure differential of 2 MPa and a temperature of 50 °C. The changes in the mechanical properties of the shale before and after immersion in drilling fluid were determined. Based on the experimental results, combined with the spring combination model and fault activation theory, a quantitative evaluation of fault activation risk was conducted. The findings revealed that the shale in this region has a high clay content, demonstrating a certain level of water sensitivity. The presence of micro-pores and micro-fractures is well-developed, increasing the interaction probability between drilling fluids and clay minerals. After immersion in drilling fluid, there was a varied decline in all mechanical strengths of the shale. The elastic modulus is positively correlated with the shear strength and Coulomb stress of the fault plane. The Poisson’s ratio is positively correlated with the shear strength and negatively correlated with the Coulomb stress. The greater the internal friction and cohesion, the higher the shear strength of the fault plane, and the larger the friction coefficient, the smaller the Coulomb stress, resulting in a more stable fault.

Objective The MS 6.8 earthquake that struck Luding County, Sichuan Province, on September 5, 2022, and its aftershocks have drawn widespread attention, especially concerning the potential risks of induced seismicity associated with the construction of high-dam reservoirs in regions with high seismic intensity. Previous studies have explored the possible link between reservoirs and seismic activity, without reaching a definitive conclusion. This study aims to assess the impact of water storage in the Dagangshan Reservoir on the surrounding strata and its correlation with recent seismic events. Methods Numerical simulation methods were employed using high-precision digital elevation model (DEM) data, fault data, and reservoir water level information to develop a three-dimensional poroelastic finite element numerical model extending from the surface to a depth of 25 km. By analyzing the hydrogeological conditions, lithology of rock masses, and groundwater dynamic changes, this study evaluated the seismic hazard risk of major faults, such as the Moxi Fault, and calculated variations in Coulomb stress and strata pore pressure at the hypocenter during the occurrence of the earthquake. Results The study indicates that, during the MS 6.8 Luding earthquake on September 5, 2022, the pore pressure at the epicenter reached 5 kPa, and the Coulomb stress increased by 3.6 kPa, suggesting that the impoundment of the Dagangshan Reservoir contributed to an increased risk along the Moxi Fault on the northwestern side of the reservoir. Using the source parameters of the MS 5.6 aftershock that occurred on January 26, 2023, it was observed that the impoundment caused a change in Coulomb stress at the epicenter of -0.69 kPa and a pore pressure of approximately 0.32 kPa. It is evident that the reservoir impoundment had a relatively minor impact on the fault activity where the MS 5.6 aftershock occurred and even exhibited a certain inhibitory effect. Moreover, seismic activity was mainly concentrated in two areas on the western side of the reservoir, with both the seismicity and expected magnitudes in these regions reflecting a higher risk of earthquakes. Conclusion This study demonstrates a correlation between the impoundment activities of the Dagangshan Reservoir and the occurrence of the Luding County earthquake and its aftershocks. The spatial distribution characteristics of the earthquakes align with the geological stress adjustment patterns following the reservoir impoundment, which played a promotive role in the occurrence of the MS 6.8 main shock, leading to an increased risk of earthquakes in the Moxi Fault region. This finding is significant for understanding the mechanisms of reservoir-induced earthquakes, subsequent aftershock analyses, and earthquake disaster prevention and mitigation efforts. Significance The results of this study provide new insights into the complex relationship between reservoir water storage and seismic events. This study offers a scientific basis for future assessments of seismic risks of reservoir design and operation, contributing to improved accuracy in earthquake early warnings and efficiency in disaster prevention and mitigation efforts.

Because of its complex tectonic setting, the Philippines experiences vigorous seismic activity. On December 15, 2019, an Mw 6.8 earthquake struck Davao del Sur, the Philippines, severely damaging infrastructure and adversely affecting the population. In this study, we used Interferometry Synthetic Aperture Radar (InSAR) and teleseismic broadband data to explore the earthquake’s source parameters, rupture process, and tectonic characteristics through a Bayesian modeling approach and Coulomb stress analysis. An analysis of InSAR suggested that the mainshock occurred on an NW–SE oriented single plane within the Cotabato fault system, with the Makilala-Malungon fault being the causative fault. The Joint inversion revealed that the rupture initiated in the middle crust (depth: approximately 16.5 km), exhibiting a blind, left-lateral strike-slip fault rupture propagation with minimal reverse slip and no surface rupture. The slip was concentrated in a distinct asperity spanning a depth of 3–24 km, with the peak slip reaching approximately 1.8 m. The source time function of this event indicated a single pulse with a total source duration of approximately 17 s. The static stress drop value was low, which may be related to the brittle condition of the crust. Coulomb stress changes calculations suggested earthquake risk in the future.

AbstractAs the forefront of the northeastern margin of the Tibetan Plateau, the Liupanshan area is subjected to significant Cenozoic deformation. Considering the background of historical earthquakes and the current seismic activity, the Liupanshan fault poses a risk of strong earthquakes. This paper analyzes the evolution of Coulomb stress induced by the coseismic and postseismic viscoelastic deformation of six historical strong earthquakes that occurred around the Liupanshan area since the twentieth century. Additionally, based on the disturbance in Coulomb stress and the background seismicity rate, the probability of earthquake occurrence is quantitatively evaluated using the frictional constitutive law. The results indicate that northern section of the Liupanshan fault has higher earthquake potential than the southern section, warranting close attention. These findings serve as a reference for medium- and long-term earthquake forecast and risk assessment in the vicinity of the Liupanshan fault.

Indonesia is a region that experiences frequent earthquakes, and therefore is highly prone to earthquake hazards. Elevated seismicity in Indonesia means that building models to understand and predict earthquake characteristics and their associated hazards is important. The goal of this research is to develop a supervised learning artificial neural network (ANN) application that can predict the magnitude of earthquake wave propagation (bar) and the direction of propagation of earthquake wave using some selected earthquake data (Mw 5-8) happened in Indonesia from 1996 to 2019. The data was taken from the United States Geological Survey (USGS) database and the Indonesian Agency for Meteorological, Climatological, and Geophysics (BMKG) database. The earthquake data used in the artificial neural network application consists of a hidden layer with four neurons and seven input neurons that contain earthquake parameters, including longitude, latitude, magnitude, depth, strike, dip, and rake, as well as one output neuron. The magnitude and direction of energy propagation of the earthquakes were successfully predicted using the ANN program. Excellent agreement between the results of ANN and those of Coulomb 3.3 software strongly indicates that the ANN program can be used as an alternative to the existing Coulomb 3.3 software. The ANN model can also be further applied to other earthquake data around the world. The results are expected to contribute to the development of earthquake detection software tools. With artificial intelligence, earthquake prediction software will be more effective and can reduce the risks of failure in predicting the magnitude and direction of earthquake wave propagation. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Geomechanics is the property of Journal of Geomechanics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Shanxi Graben is a transitional zone between the Ordos Block and North China Plain with complex structures and frequent earthquakes. Six earthquakes with M ≥ 7.0 have been recorded in the area, including the 1303 Hongtong M 8 and 1695 Linfen M 7.8 earthquakes in the Linfen Basin. Research on these two large earthquakes, closely related in time and space, is lacking. Our objective was to use deep seismic reflection profiles and 3D velocity structure data from previous research, along with seismological observation results, to interpret the geological structure near the source of the two earthquakes. A 3D geometric model of the seismogenic fault was constructed, and the relationships among the deep and shallow structures, deep seismogenic environment, and two large earthquakes were explored. Differences in seismogenic environment between the southern and northern Linfen Basin were identified. The distribution of small earthquakes in the southern Linfen Basin was scattered, and the overall distribution was at depths Mw 7.7, so the magnitude of the 1303 Hongtong earthquake might be overestimated. Numerical simulation results of Coulomb stress showed that the 1303 Hongtong earthquake had a stress-loading effect on the 1695 Linfen earthquake. The change in Coulomb rupture stress was 1.008–2.543 bar, which is higher than the generally considered earthquake trigger threshold (0.1 bar). We created a new 3D source model of large earthquakes in the Linfen Basin, Shanxi Province, providing a reference and typical cases for risk assessment of large earthquakes in different regions of the Shanxi Graben.

A detailed spatial-temporal analysis of the seismic activity in and around the Lake Van region was performed using several seismotectonic parameters such as b-value, Z-value, relative intensity (RI), pattern informatics (PI), and Coulomb stress changes. Correlations between these parameters were analyzed to estimate and forecast potential seismic hazards in the Lake Van region. Particular attention was paid to the parts of the study region that exhibited smaller b-values, higher Z-values, and high-stress changes at the beginning of 2022 and to the locations of earthquake hotspots determined from the composite earthquake forecast map for 2022-2032, i.e., Muradiye, Çaldıran, Özalp, Erçek, Van city center and Gevaş covering the faults of Çaldıran, Yeniköşk, Erciş, Malazgirt and the fault zones of Saray and Van. To provide more accurate interpretations regarding potential earthquake occurrences in the near future, the seismotectonic parameters analyzed in the scope of this study were compared with the corresponding seismological, geological, geodetical, and geochemical variables reported in the literature. This comparison showed that, firstly, our results are consistent with those reported in previous studies, and, secondly, all these variables should be interpreted in combination to correctly assess strong earthquake hazards. Furthermore, this type of multiple-parameter analysis may be important for the description of seismic, tectonic, and structural characteristics of the nature of the crust. Our findings show that almost all seismotectonic parameters indicative of anomaly regions, i.e., lower b-values, higher Z-values, high-stress distribution, and hotspots, were recorded in the same parts of the study region. Thus, the anomaly regions detected at the beginning of 2019 and between 2022 and 2032 may be considered to be potential zones of future great earthquakes. To summarize, the correlations among these variables may provide accurate information for assessing and forecasting earthquake hazards in this region. [ABSTRACT FROM AUTHOR]

Increasing energy demand and high world oil prices are making countries turn to geothermal energy use. Indonesia is a country that has geothermal energy due to Indonesia's geographical location and geological conditions, which is located between three active earth plates so that Indonesia has 240 volcanoes and often experiences earthquakes. The 2003-2013 earthquake data obtained are coordinates, magnitude, depth, focal mechanism and all these data are analyzed in the coulomb stress method. Rianiate geothermal measurement data in March 2013 included geothermal location, hotspring and air temperature, pH, and geochemical measurements. The analysis results showed that the highest coulomb stress value was at a depth of 90 km of 0.56 bar while the shear and normal values were 0.452 bar and 0.251 bar. The result of the spread of coulomb stress is to the northeast, east and southeast. Then the results of the analysis of the direction of distribution of coulomb stress are compared to the location of the hotspring based on a decrease in temperature, the change in the potential of hotspring 1 leads to hotspring 2, 3, and 4 in the opposite direction, namely northwest or leads to the largest source of colulomb stress, so that Coulomb Stress Changes affect indirectly changes in the geothermal potential of Rianiate

The incident of increased seismic activity of the Merapi volcano was initiated by several tectonic earthquake phenomena. Analysis of the mechanism of tectonic earthquakes can be studied based on the combination of static stress on the rock. This paper describes the distribution of the Coulomb stress changes due to the interaction that occurs in tectonic earthquakes with volcanic activity. The data in the calculation of the Coulomb stress distribution are secondary in the form of tectonic seismicity data downloaded from the ISC (International Seismological Center), USGS (United States Geological Survey), and Global CMT (Global Centroid Moment Tensor) catalogs between 2001 and 2010. Calculation results and data analysis is the occurrence of an increase in Coulomb stress response in the Merapi Volcano area with a value range of 0.2–10 kPa at a depth of 2–4 km below the peak of Merapi Volcano. The Coulomb stress changes distribution is thought to indicate the accumulation of stress due to tectonic earthquakes that downward at the top of the volcano, thereby affecting the stability of the magma chamber and causing volcanic activity at the Merapi volcano. [ABSTRACT FROM AUTHOR]

On 1 December 2016, an Mw 6.2 earthquake characterized by normal faulting occurred in the highlands of the central Andes in southern Peru, marking the region's largest shallow event. The occurrence of the earthquake provides a significant chance to gain insight into the regional tectonic deformation and the seismogenic mechanism of the shallow normal-faulting earthquake, as well as the regional potential seismic risk. Here, we first utilize Sentinel-1A interferometric synthetic aperture radar (InSAR) data to extract the coseismic and postseismic deformation associated with this earthquake and then determine the detailed coseismic slip and postseismic afterslip distribution of this event. Coseismic modeling results indicate that the coseismic rupture is mainly characterized by normal faulting with some dextral strike-slip components. Most coseismic slip is confined to a depth range of 2–12 km, indicating an obvious slip deficit area in the shallow fault part. Further postseismic modeling reveals that the majority of afterslip is concentrated at depths of 0 to 5.4 km. The relatively shallow postseismic afterslip makes up for the coseismic slip deficit area to some extent. Through a joint analysis of the inversions, seismic data, and regional geology and geomorphology, we infer that the occurrence of this 2016 normal-faulting event is a result of regional gravitational collapse. In addition, we investigate the relationship between the 2016 earthquake and great historical earthquakes near the subduction zone of the central Andes and find that the 2016 event is likely promoted in advance by these events through our calculations of the coseismic and postseismic Coulomb stress changes. Finally, we should pay more attention to the nearby Falla Huaytacucho-Condoroma fault and the western segment of the Vilcanota Fault because of their relatively high stress loading. [ABSTRACT FROM AUTHOR]

We report solid-earth tidal modulation of early aftershocks of the July 2019 Ridgecrest earthquake sequence, which occurred close to the southeastern edge of the Coso geothermal field. We found that the frequency of early aftershocks in the northern part, close to the Coso geothermal field, was modulated by the solid earth tides as they exhibit a strong correlation with the peak shear stress and Coulomb stress imparted by the solid earth tides. However, aftershocks that occurred farther south of the Coso geothermal field in the same sequence exhibit a weak correlation with the solid earth tidal stress. Our analysis implies that the tidal modulation of the earthquake sequence in the northern part is due to its vicinity to the Coso geothermal fields in southern California, which contain high-pressure fluids and are well known for their susceptibility towards tidal triggering. [ABSTRACT FROM AUTHOR]

The Kalabagh strike–slip fault, which is characterized by right-lateral movement, is part of the northwestern Himalayan foreland fold and thrust belt in Pakistan. This structure marks the western and eastern terminations of the Salt Range and Surghar Ranges, respectively. No significant (>M6) earthquakes have been reported along the Kalabagh Fault in recent decades. Here, we take advantage of space-borne Sentinel-1A SAR interferometry to gain insight into the mechanics of faulting, aseismic creeping, and stress loading of the seismic cycle on the Kalabagh Fault spanning over approximately 7 years. In this study, we also removed the tropospheric effects using the Generic Atmospheric Correction Online Service data from the rate map. We further resolved the LOS deformation into both horizontal and vertical deformations. Our Bayesian inversion indicates that the fault experiences significant horizontal and vertical displacements. The fault’s southern and northern segments exhibit a creeping rate of approximately ∼4.2 ± 1.3 to 4.8 ± 1.6 mm/year, respectively, while the central section does not display any horizontal creeping. We found that the creeping is confined between 0 and ∼2.7 ± 1.1 km depth at the northern section and 0 and ∼3.9 ± 1.1 km on the southern section of the faults. Nevertheless, we found that the vertical creeping of ∼10 mm/year is confined between 0.5 and 6 km depth in the central segment of the fault. Moreover, our model does not resolve the interseismic slip at depth on the Kalabagh Fault. Our results affirm that Kalabagh Fault is creeping, and the internal deformation due to the presence of a thick salt layer over the decollement facilitates the creeping on this fault. In addition, Coulomb stress modeling depicts that the creeping on the Kalabagh Fault increases the Coulomb stress changes in the northern section of the KBF.

The Gulf of Aqaba is considered one of the most seismotectonically active regions in the Middle East. This study analyzes the seismic activity from 1983 to 2018 to investigate the spatio-temporal distribution of the events in the Gulf's three basins. The seismic activity is characterized by conventional mainshock–aftershock sequences and swarm activity. Most activity is located in the Aragonese basin, while the Dakar basin shows less seismic activity. The b-value was calculated for the three basins from the declustered catalogue, representing the fingerprint of the transform fault. Within the Aragonese, three significant earthquakes occurred in 1993, 1995, and 2015 with moment magnitude (Mw) of 5.8, 7.2, and 5.2, respectively. An intermediate seismic quiescence preceded the three earthquakes. The quiescence time for the 1995 earthquake began at the tail of the aftershocks of the 1993 mainshock, suggesting that the two earthquakes were not entirely independent. At the tail of the 1995 earthquake aftershocks, the seismic activity spread across the Gulf, increasing in frequency and decreasing in magnitude. A similar pattern was observed for the seismic quiescence preceding the 2015 mainshock. The occurrence of the three significant and proximal earthquakes in the Aragonese region over a 22-year interval, with the described similarities, suggests a link between these earthquakes. Finally, the Coulomb stress transfer shows that the 1993 source fault seems to increase the stress loading on the 1995 left-lateral strike-slip fault, and the latter would also increase the stress transfer on the 2015 left-lateral strike-slip fault. [ABSTRACT FROM AUTHOR]

The tectonic structure of Türkiye is under the influence of Arabian, Eurasian, African, and Anatolian plates. Lake Van region, located in eastern Türkiye, has been exposed to many devastating earthquakes in historical and instrumental periods. In this paper, using regional earthquakes, the tectonic stress variation of Lake Van region was investigated using the Coulomb stress change and the b-value distribution. 83 earthquakes that occurred between 2000 and 2020 are used to calculate the Coulomb stress change, while 17815 earthquakes that occurred between 1903 and 2021 are used to calculate the b-value distribution. Coulomb stress change gives an idea about the transfer of energy to nearby faults. Coulomb stress change and b-value distribution maps were created atdifferent depths to model the variation of stress. The low b-values and positive Coulomb stress values were especially observed around the Van and Yeniköşk faults. On the contrary, no significant variation in stress change was observed around Süphan and Nemrut volcanoes, and high b-values were calculated in this region. Coulomb stress change and earthquake epicentral distribution are compatible and most events occurred in positive stress regions. In conclusion, stress change and b-value distribution were interpreted together and positive stress regions were revealed in the region.

Copyright of Journal of Geodesy & Geodynamics (1671-5942) is the property of Editorial Board Journal of Geodesy & Geodynamics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We map surface deformation in the Thrace region of Turkey using the Sentinel-1 Synthetic Aperture Radar (SAR) data. Interferometric Synthetic Aperture Radar (InSAR) time series analysis of the SAR data acquired between 2014 and 2020 on ascending and descending orbits reveals large-scale subsidence (~110 x 60 km) with rates reaching up to 10 ± 1.5 mm/yr. We relate this deformation to natural gas reservoir operations, such as gas exploitation and extraction activities that have been taking place in the region for decades, an inference being supported by the strong correlation between the InSAR time series and the variation in natural gas production during the same time period in the Thrace region reported by the Energy Market Regulation Authority of Turkey. Assuming that the observed subsidence is caused by compaction of sediments in the natural gas reservoirs, we construct a triangulated surface enveloping roughly at the bottom of the gas extraction wells and use it to invert the amount of negative opening (hence volume loss) on triangular elements that are assumed to be buried in an elastic and homogeneous medium. Coulomb stress changes caused by this volume change on the North Anatolian Fault at the Sea of Marmara are found to be insignificant (less than 10-5 Mega-Pascal) to perturb the state of the stress around the Marmara seismic gap. Yet, the large-scale subsidence revealed in this study needs to be taken into consideration when assessing hazards for the infrastructures, settlements, and other engineering structures, particularly in case of a large earthquake in the Marmara Seismic Gap. [ABSTRACT FROM AUTHOR]

On 23 January and 25 March 2022, two MW > 5.5 Hala Lake earthquakes characterized by right-lateral strike-slip faulting occurred around the Elashan Fault in Northeastern Tibet, marking the two largest events since the 1927 MW 6.2 Hala Lake earthquake. Since no surface rupture related to the two earthquakes has been reported, the seismogenic faults and coseismic rupture behaviors of the two events are still unknown. The occurrence of the two events provides a rare opportunity to gain insight into the seismogenic structure and rupture behavior of the less studied region, further helping us accurately evaluate the regional seismic hazard. Here, we first exploit Interferometric synthetic aperture radar (InSAR) data to obtain the coseismic deformation associated with the two earthquakes and then invert for the fault geometry and detailed coseismic slip of the two events. Coseismic modeling reveals that the January and March 2022 earthquakes ruptured two buried west-dipping moderate-angle and high-angle right-lateral strike-slip faults, respectively. Most of the slip of the January event occurred at depths from 1.7–7.6 km, while the majority of the slip associated with the March event occurred at depths from 2.5–10 km, which may have been restricted by the intersections between the January and March Hala Lake seismogenic faults. By a comprehensive analysis of the coseismic inversions, stress changes, and early postseismic signal, we suggest that the significant fault dip difference (~30°), highlighting a fault segmentation, stops the rupture propagation from one fault segment to another and that fluid migration may encourage the restart of the rupture of the later event, which requires further investigation. Moreover, Coulomb stress modeling shows stress loading on the eastern segment of the Daxueshan–Shule Fault and the northern segment of the Elashan fault, which we should pay more attention to. [ABSTRACT FROM AUTHOR]

On 8 January 2022, a Moment Magnitude (Mw) 6.7 earthquake occurred in Menyuan, China. The epicenter was located in the western segment of the Lenglongling fault of the Qilian-Haiyuan fault zone. In this area, the Mw 5.9 Menyuan earthquake on 26 August 1986 and the Mw 5.9 Menyuan earthquake on 21 January 2016 successively occurred. The seismogenic structures of the 1986 and 2016 earthquakes are on the Northern Lenglongling fault, which is a few kilometers away from the Lenglongling fault. After the 2022 Menyuan earthquake, we collected GF-7 and Sentinel-1 satellite images to measure the surface deformation of the earthquake sequence. Based on the elastic dislocation theory, the fault model and fault slip distribution of the 2016 and 2022 Mengyuan earthquakes were inverted using coseismic surface displacements. The results show that the 2016 event is a reverse event, with the maximum coseismic surface displacement on LOS reaching 8 cm. The strike, dip, and rake of the earthquake rupture were 139°, 41°, and 78°, with the maximum slip reaching 0.6 m at a depth of 8 km. The surface rupture of the 2022 Mw 6.7 earthquake ran in the WNW–ESE direction with a maximum displacement on LOS of 72 cm. The main seismogenic fault of the 2022 event was the western segment of the Lenglongling fault. The strike, dip, and rake of the rupture were 112°, 85°, and 3°, with the maximum slip reaching 4 m at a depth of 4 km. The Coulomb failure stress change shows that the earthquake sequence generated a considerable positive Coulomb failure stress of more than 2 bar. These observations suggest that the earthquake sequence around Menyuan is mainly governed by the activities of the Lenglongling fault around the northeastern Tibetan Plateau. In addition, their sequential occurrences could be related to earthquake-triggering mechanisms due to stress interaction on different deforming faults. Thus, the Lenglongling fault has received a great amount of attention regarding its potential earthquake hazards. [ABSTRACT FROM AUTHOR]

To analyze the influence of the 2008 Wenchuan MS8.0 earthquake on later earthquakes and the characteristics of the tectonic stress field in the seismogenic region, we first used 1660 source mechanism solutions of the Wenchuan earthquake and its neighboring areas from May 12, 2008 to April 19, 2013, and also used the method of sieving the central solution of multiple source mechanism solutions of the same earthquake to remove the source mechanism solutions of repeated seismic events, and finally 911 solutions were obtained. Then, the regional tectonic stress field is inverse-performed by the grid search method. The results show that the northeast zone is mainly squeezed by the WNW-ESE direction, the southwest zone is squeezed by the W-E direction, and the central zone is squeezed by the WSW-ENE direction. There is a change in the direction of the main compressive stress axis from southwest to northeast, which may be related to the combined effect of subduction thrusting from the north-northeast direction of the Indian plate, blocking from the Sichuan basin and southeastward extrusion of the Bayan Kara block in the Longmenshan area. Then, based on the rupture model of the Wenchuan MS8.0 earthquake given by the USGS, the triggering relationship of this earthquake on nearby strong earthquakes is calculated. The results show that this Wenchuan earthquake has a significant triggering effect on the Lushan earthquake, which also belongs to the southwest end of the Longmenshan fault, and on the Maduo earthquake, which is located on the East Kunlun fault. Finally, the coseismic Coulomb stress changes of the surrounding faults caused by the Wenchuan MS8.0 earthquake were calculated. It is found that this earthquake caused an increase in Coulomb rupture stress on the north and south ends of the Longmenshan fault, the south edge of the Qinling fault, the southeast end of the Xianshui River fault, the East Kunlun fault, and the Baiyu fault, with the most obvious increase on the north and south ends of the Longmenshan fault and the south edge of the Qinling fault, which is a reference for the analysis of seismic hazards.

In March 2021, a seismic sequence including three Mw>5.5 events struck northern Thessaly, Greece. Owing to the high temporal resolution of Sentinel-1 images which were sampled every 6 days and recorded the three events separately, we are able to map individually the coseismic deformation fields of the three events. Based on their respective coseismic displacements, we determined the geometry of the fault plane for each earthquake with the method of multipeak particle swarm optimization and inverted the best-fitting slip distribution by linear least squares inversion. Modelling results show that the three events occurred successively on 3, 4 and 12 March 2021 were all dominated by normal-slip motions on previously unknown faults within the top 15km of the Earth’s crust. The 3 March 2021 Mw 6.3 earthquake ruptured a northeast-dipping fault with a strike angle of 301° (clockwise from the North) and a dip angle of 46°, producing the maximum slip of about 2.2m. The slip motion of the 4 March 2021 Mw 5.9 aftershock shows a similar fault geometry (striking 297° and dipping 42°) to the 3 March mainshock, but with a considerably smaller dip-slip component (~0.8m). The 12 March 2021 Mw 5.6 aftershock occurred on a southwest-dipping fault (striking 100° and dipping 40°) with a normal fault slip of up to 0.5m. Static Coulomb stress changes triggered by the earthquake sequence imply a promotion relationship between the first 3 March event and the two subsequent events. Due to the coseismic stress perturbation, more than 70% of aftershocks were distributed in areas with increased Coulomb stress and the northwest segment of the Larissa fault close to the seismic sequence was exposed to a relatively high seismic risk.

• We built a high-precision earthquake catalog for the Weiyuan shale gas revealing detailed seismicity. • Earthquake swarms in this field indicate a complex fault system. • The 2019 Ms 5.2 earthquake may be triggered by to combination effects of fluid pressure and stress perturbation. The Weiyuan-Rongxian shale gas field in the Sichuan basin, China, has experienced numerous earthquakes in recent years, causing significant casualties and property loss. To investigate the spatial–temporal evolution of seismicity and seismic fault structures, in this study, we first utilize a deep-learning-based picking algorithm –(PhaseNet) to identify seismic phases from raw seismic data between March 2019 and October 2020, and then employ a Rapid Earthquake Association and Location technique (REAL) to associate these seismic picks. Finally, the VELEST and GrowClust methods are performed to build a high-precision earthquake catalog containing 18,912 earthquakes. Our results reveal that the spatial–temporal distribution of earthquake swarms indicates a complex fault system. In the northern part of Weidong block (R1), the earthquakes illuminate a shovel-shaped structure that the dip angle of the fault plane gradually decreases with depth. In the south of Weidong block (R2), the natural fractures with dip angles of about 80° control the distribution pattern of earthquakes. In the Weixi block (R3), the Molin fault and basement fault form a typical structural wedge that bounds a triangular or wedge-shaped fault block. The majority of earthquakes located below the buried depth of the shale gas and spatio-temporal correlations between seismicity and industry operations both suggest that they are probably induced by hydraulic fracturing. The migration front of the earthquakes can be modeled by fluid diffusion with the diffusivity D between 0.2 m2/s and 3.5 m2/s. The Ms 5.2 earthquake occurring on 18 December 2019 is located in a positive ∼10 kpa Coulomb failure stress area generated by the 8 September 2019, Ms 5.4 earthquake, reaching the typical static triggering threshold. Therefore, in addition to fluid diffusion, the stress perturbation caused by previous seismic ruptures may be considered as another factor of earthquakes occurring in the Weiyuan-Rongxian. Our study provides evidences for better understanding the seismicity characteristics, seismogenic mechanism, and fault structure in Weiyuan-Rongxian shale gas field. [ABSTRACT FROM AUTHOR]

On 1 December 2016, an Mw 6.2 earthquake characterized by normal faulting occurred in the highlands of the central Andes in southern Peru, marking the region’s largest shallow event. The occurrence of the earthquake provides a significant chance to gain insight into the regional tectonic deformation and the seismogenic mechanism of the shallow normal-faulting earthquake, as well as the regional potential seismic risk. Here, we first utilize Sentinel-1A interferometric synthetic aperture radar (InSAR) data to extract the coseismic and postseismic deformation associated with this earthquake and then determine the detailed coseismic slip and postseismic afterslip distribution of this event. Coseismic modeling results indicate that the coseismic rupture is mainly characterized by normal faulting with some dextral strike-slip components. Most coseismic slip is confined to a depth range of 2–12 km, indicating an obvious slip deficit area in the shallow fault part. Further postseismic modeling reveals that the majority of afterslip is concentrated at depths of 0 to 5.4 km. The relatively shallow postseismic afterslip makes up for the coseismic slip deficit area to some extent. Through a joint analysis of the inversions, seismic data, and regional geology and geomorphology, we infer that the occurrence of this 2016 normal-faulting event is a result of regional gravitational collapse. In addition, we investigate the relationship between the 2016 earthquake and great historical earthquakes near the subduction zone of the central Andes and find that the 2016 event is likely promoted in advance by these events through our calculations of the coseismic and postseismic Coulomb stress changes. Finally, we should pay more attention to the nearby Falla Huaytacucho-Condoroma fault and the western segment of the Vilcanota Fault because of their relatively high stress loading.

Sorik Marapi is an active volcanic mountain with an altitude of 2,145 meters located in Batang Gadis National Park, Sibanggor Julu Village, Mandailing Natal Regency, North Sumatra, Indonesia. Since the earthquake in Aceh on December 26, 2004, geological conditions in the western part of Sumatra Island have increased in stress. This affects the volcano in Sumatra, Mount Sorik Marapi, so it needs to be studied to find out the condition of changes in coulomb stress in Sorik Marapi. The method used in this study is a descriptive method with an analysis of the coulomb stress method. From the Aceh earthquake year of December 2004 to 2021, Mount Sorik Marapi experienced the highest average increase in coulomb stress in 2012, which was 0.171 bars. The highest average increase in shear in 2015 was 0.25 bars, and the highest average normal increase in 2018 was 0.202 bars. While at depth, Sorik Marapi mountain experienced an average change in coulomb stress highest of 0.368 bars, the average increase in the highest shear by 0.269 bars, and the average normal increase of 0.246 bars. All such increases are at a depth of 90 km below sea level. Based on the results of this study, it is stated that Mount Sorik Marapi experiences inconsistent changes in coulomb stress every year.

Based on geological conditions, Indonesia is located between the Indo-Australian plate, the Eurasian plate, and the Pacific plate, making Indonesia prone to tectonic earthquakes. However, since the big earthquake that occurred in Aceh on December 26, 2004, the geological conditions in Sumatra have undergone significant changes marked by stressful situations in the western to southern regions of Sumatra, especially on Sibayak Volcano. This study used data from BMKG and Global CMT, which included magnitude (Mw), depth, earthquake coordinates (longitude and latitude), type of earthquake, strike, dip, and rake. From the analysis using Coulomb 3.3, the highest coulomb stress value of Sibayak Volcano was obtained in 2015 with an average change in coulomb stress of 0.235 bar, shear 0.1909 bar, normal 0.1106 bar. However, the lowest coulomb stress value occurs in 2021 with a moderate shift in coulomb stress of 0.0593 bar, shear 0.0251, normal 0.0849 bar.

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Mamasa, located in West Sulawesi, Indonesia, is a populous dense area with a low seismic hazard. In this area, the question of fault reactivation was raised due to the 804 reported earthquakes from November 2018 to February 2019. This series does not show an apparently major earthquake or behaviors, such as swarms. One month earlier, on 28 September 2018, the 7.6 Mw Palu earthquake occurred at a distance of approximately 230 km north of Mamasa. It affected the occurrence of this swarm since Mamasa has many hydrothermal manifestations, which have been linked with seismic activity. To investigate the roles of these two factors, the series of earthquakes and their possible linked faults must be characterized. Specifically, the double-difference hypocenter relocation method was used to relocate the earthquakes and conduct a spatiotemporal analysis of this swarm. Furthermore, the FHD (first horizontal derivative) gravity data were used to illuminate the possible linked fault. To assess the impact of the Palu earthquake, the Coulomb stress was calculated, and it was reported that it was very small. Therefore, it played an insignificant role in triggering the swarm. In contrast, the relocated earthquakes are concentrated in an area surrounded by surface hydrothermal manifestations, and the swarm feature is consistent with the interpretation of associated seismicity. Therefore, hydrothermal activities play a critical role in triggering the swarm. [ABSTRACT FROM AUTHOR]

This paper considers theoretical aspects of a trigger effect of earth tides on earthquake initiation under the LURR approach. The growth of Coulomb stress, which appears resulting from this phenomenon, is shown to occur not for all regimes of stress state acting in the studied region. Its greatest increase corresponds to the regime of the horizontal extension and shear associated with the faults with kinematics of the normal and strike-slip faults. The low level of additional Coulomb stress for the horizontal compression regime allows asserting the low probability of the trigger effect for the faults with kinematics of the reverse faults. It is noted, that there is also an indirect factor in the form of additional pressure caused by the sea tides in addition to the main factor of the earth tides effect on deformations in the solid earth for island arcs and coastal areas of the continental crust. This is an additional vertical pressure for the ocean floor, and a lateral pressure for the crust of island arcs and coastal areas of the continents. Indirect factors significantly complicate the effect of earth tides on the Earth’s crust, completely neutralizing the influence of the direct factor in some cases.

Using the analytical approximation method, we calculated stress field parameters for cases with different relative positions of Riedel shears and loads required for shearing. Considering an internal friction angle of 30°, and the distance between adjacent shears exceeding 0.7 of the characteristic shear length, we estimated the Coulomb stress that can lead to fracturing. In the areas between the shears, it is below the shear strength value. This means that if an increase in the external load is lacking, there are no prerequisites for the formation of new fractures that may connect adjacent shears. If the shears are spaced closer to each other (i.e. at distances less than 0.7 of the shear length), the shear strength is exceeded in the areas between them, and new shears can occur there and connect the Riedel shears to each other. Therefore, in observations of a natural system of Riedel shears, it becomes possible to assess whether this system is sufficiently stable in its current status, or, in case of a critical increase in the Coulomb stress in the areas between adjacent shears, the equilibrium can be easily disturbed, and there is a possibility that the main fault forms in the strike-slip zone under study.

The Kachchh Rift Basin (KRB) is a very peculiar region in the Indian subcontinent mostly due to the intense seismic activity and intricate tectonics that is located far from the active plate boundaries. The KRB region is located in the Deccan Volcanic Province of Western India. Recently, a moderate earthquake (Mw5.3) occurred in this region on June 14, 2020, that was followed by ~ 22 earthquakes (M ≤ 4.6) until June 23, 2020. This moderate-size event falls about 12 km SSE from the 2001 Bhuj earthquake (Mw7.6). The mainshock and aftershocks are found to be located in an area of ~ 20 × 20 km2 that is orienting NE-SW indicating the rupture area of the mainshock. Several pertinent questions arose for the recent moderate event as it was located in the vicinity of the 2001 mainshock. The estimated focal mechanism solution of the current event depicts reverse faulting with a small strike-slip component. The current seismic activity matches well with the south-dipping nodal plane that is akin to the South Wagad Fault (SWF) in the region. The Coulomb failure stress change (∆CFS) caused due to the 2020 mainshock, considering the source as a receiver fault, clearly demonstrates the locations of aftershocks in the zone of compression that corroborates well with the south-dipping source. Such a strong correlation between the static stress changes and the aftershocks indicated SWF as the causative source. Interestingly, we found that the recent earthquake sequence has occurred in the shadow zone of the 2001 Bhuj mainshock. The coseismic deformation due to the 2020 mainshock was also obtained using an InSAR interferogram that demonstrated coseismic subsidence of ~ 3.6 cm close to the source zone, which is found to be consistent with the activity along with the south-dipping SWF. In addition, the low seismic velocities (Vp, Vs), high Vp/Vs ratio, and positive Coulomb stress changes suggest entrapped magma fluid in the seismogenic rock matrix, which probably played a significant role in triggering earthquakes in the study region. We validated our observations with the earlier seismological, geophysical, and geological shreds of evidence. [ABSTRACT FROM AUTHOR]

On May 21, 2021, Yangbi Mw 6.4 earthquake occurred in Dali area of Yunnan, China. However, the pre-research on the geological structure in the seismogenic area of this earthquake is weak. It is scientific for the in-depth understanding of the seismogenic, seismogenic mechanism and characteristics of tectonic activity in Yangbi area and its adjacent areas to monitoring and inversing source parameter for this earthquake. The Senital-1A SAR satellite images of ESA were used to obtain the co-seismic deformation field of the earthquake from different orbits, and the Okada rectangle elastic dislocation model was used to invert the earthquake source parameters and the co-seismic slip distribution. The results show that the maximum uplift and maximum subsidence deformation caused by co-seismic rupture are both over 10cm. The inversion results of the co-seismic show that the earthquake is caused by the rupture of a fault with a length of 12.2 km, a width of 5.0 km, a strike of 132° and a dip angle of 83°; the earthquake is a significant right-lateral strike-slip movement. The average slip is 0.19 m and the average slip angle is -153.6°, and the magnitude is Mw 6.1, which is consistent with the focal mechanism solution published by USGS and GCMT. At the same time, Coulomb stress of co-seismic is 4.21×1025 dyne.cm-1, which is equivalent to Mw 6.38; and Coulomb stress distribution reflects that the earthquake is dominated by stress release, which further triggers strike-slip earthquake unlikely [ABSTRACT FROM AUTHOR]

The tectonic structure of Türkiye is under the influence of Arabian, Eurasian, African, and Anatolian plates. Lake Van region, located in eastern Türkiye, has been exposed to many devastating earthquakes in historical and instrumental periods. In this paper, using regional earthquakes, the tectonic stress variation of Lake Van region was investigated using the Coulomb stress change and the b-value distribution. 83 earthquakes that occurred between 2000 and 2020 are used to calculate the Coulomb stress change, while 17815 earthquakes that occurred between 1903 and 2021 are used to calculate the b-value distribution. Coulomb stress change gives an idea about the transfer of energy to nearby faults. Coulomb stress change and b-value distribution maps were created at different depths to model the variation of stress. The low b-values and positive Coulomb stress values were especially observed around the Van and Yeniköşk faults. On the contrary, no significant variation in stress change was observed around Süphan and Nemrut volcanoes, and high b-values were calculated in this region. Coulomb stress change and earthquake epicentral distribution are compatible and most events occurred in positive stress regions. In conclusion, stress change and b-value distribution were interpreted together and positive stress regions were revealed in the region. [ABSTRACT FROM AUTHOR]

On March 10, 2011, an Ms. 5.8 earthquake struck Yingjiang City, western Yunnan, China, causing destructive damage. Due to the very sparse distribution of seismic stations on the southwestern border of China, its seismogenic structure and mechanism remain controversial. In this study, with the aid of machine-learning-based detection and location workflow and template matching technique, we detect 10,356 events ranging from December 1, 2010, to April 30, 2011. The high-precision earthquake catalog shows that the foreshocks initiated in the extensional stepover connecting the northeast and middle segments of the Dayingjiang fault and then bilaterally extended northeast and southwest, with migration fronts that can be simulated by fluid diffusion model with diffusivities of 0.8 m2/s and 0.19 m2/s, respectively. The mainshock occurred at the southwest end of the foreshock sequence and then probably activated the northwest-trending blind fault. In addition, we determine the full moment tensor solutions for the mainshock, six large foreshocks, and one aftershock, with magnitudes ranging from 3.03 to 5.80, in which the mainshock was characterized by an obvious negative isotropic (ISO) component. The static Coulomb failure stress change caused by five Mw ≥ 4.0 foreshocks on the mainshock fault plane is ∼24 kPa, reaching the typical static triggering threshold. Therefore, we suggest that both the fluid diffusion and stress perturbation contribute to triggering the mainshock. This study advances our understanding of the spatiotemporal evolution, seismogenic mechanism, and hazard implication for the Yingjiang Ms. 5.8 earthquake and provides additional evidence of natural fluid-triggered seismicity in western Yunnan. • We detect 10,356 events for the 2011 Yingjiang Ms. 5.8 earthquake sequence. • Our result reveals a foreshock sequence that could be related to fluid diffusion. • Both the fluid diffusion and stress perturbation contribute to triggering the mainshock. [ABSTRACT FROM AUTHOR]

On 19 January 2020, an Mw6.0 earthquake occurred in Jiashi County, Xinjiang, China. This earthquake is a strong earthquake that occurred in the Kepingtage Belt. The monitoring and inversion of the co-seismic and post-earthquake will help further understand the geometry and movement properties of this tectonic belt. In this study, Sentinel-1A images were used to analyze the deformation of co-seismic and post-seismic events. The Okada elastic dislocation model was used to invert the geometric parameters of the fault and co-seismic slip distribution. The results showed that the maximum uplift and maximum subsidence deformations from the ascending images were 55 and 45 mm, respectively. The maximum uplift and subsidence deformations from the descending images were 62 and 28 mm, respectively. The inversion results show that the earthquake was induced by a fault with a length of 23.5 km, width of 4.7 km, and depth of 7.2 km. This earthquake was a typical dip-slip event. The distributed inversion results of post-earthquake deformation show that the maximum co-seismic slip and maximum post-seismic slip are located on the same fault plane, mainly distributed on the edge of the co-seismic fault, between the two faults.

On 8 January 2022, an Ms 6.9 earthquake occurred in Menyuan County, Qinghai Province, China. This earthquake ruptured a patch of the Qilian-Haiyuan fault in the northeast margin of the Qinghai-Tibet Plateau. In order to understand the seismogenic structure of this earthquake and analyze the fault activity, we use differential synthetic aperture radar interferometry (D-InSAR) technology to obtain a complete co-seismic displacement field on the surface, and use pixel tracking algorithm to extract the trace of the ruptured fault. The slip distribution of the seismogenic fault was inverted using the steepest descent method, and the Coulomb stress change caused by the earthquake was also calculated. Surface deformation results show that the Menyuan earthquake produced obvious surface displacements in an area of 50 × 40 km2. The displacements are mainly distributed in the western segment of the Lenglongling fault and the eastern segment of the Tolaishan fault. The maximum displacements in the ascending and descending orbits in the LOS direction are 59.7 and 94.7 cm, respectively. The co-seismic slip results show that the strike, dip and average slip angles of the seismogenic fault are 108°, 79° dipping to SW, and 4°, respectively. On the whole, the fault is mainly of left-lateral, with a small amount of thrust component and only one co-seismic rupture center in our inversion result. The rupture center is located at a depth of ∼5 km below the surface, and the maximum slip is 3.1 m. The total seismic moment released by this earthquake is 1.28 × 1019 N·m, and the corresponding moment magnitude is 6.67. Finally, the static Coulomb stress change results show that parts of the Lenglongling fault, the Tolaishan fault, the Sunan-Qilian fault and the Minyue-Damaging fault are loaded, emphasizing the importance for earthquake risk assessment of these fault.

The coseismic and postseismic effects are crucial elements in analyzing fault interactions and the regional seismic risk. In this paper, we developed a three-dimensional viscoelastic finite element code to simulate the coseismic and postseismic deformation. We calculated the coseismic and postseismic deformations caused by the strike-slip fault with a conceptual model, and compared the results with the analytic and semi-analytic solutions so as to verify the reliability of the code. Meanwhile, we also analyzed the influence of different parameters on the coseismic and postseismic deformation, uncovering a significant effect of the earth's lateral heterogeneity on the coseismic displacement. And the viscosity of the middle-lower crust and upper mantle plays a major role in controlling the postseismic displacement. At last, we used the three-dimensional viscoelastic model to calculate the changes of the coseismic and postseismic Coulomb stress caused by the 2008 MW7.9 Wenchuan earthquake, and analyzed the subsequent effect on the 2013 MW6.6 Lushan earthquake and the 2017 MW6.5 Jiuzhaigou earthquake. The calculation results show that the Coulomb stress changes caused by the Wenchuan earthquake is positive near the hypocenters of the Lushan earthquake (0.013 MPa) and the Jiuzhaigou earthquake (0.009 MPa), indicating the Wenchuan earthquake might have triggered both the Lushan earthquake and Jiuzhaigou earthquake.

On 23 January and 25 March 2022, two MW > 5.5 Hala Lake earthquakes characterized by right-lateral strike-slip faulting occurred around the Elashan Fault in Northeastern Tibet, marking the two largest events since the 1927 MW 6.2 Hala Lake earthquake. Since no surface rupture related to the two earthquakes has been reported, the seismogenic faults and coseismic rupture behaviors of the two events are still unknown. The occurrence of the two events provides a rare opportunity to gain insight into the seismogenic structure and rupture behavior of the less studied region, further helping us accurately evaluate the regional seismic hazard. Here, we first exploit Interferometric synthetic aperture radar (InSAR) data to obtain the coseismic deformation associated with the two earthquakes and then invert for the fault geometry and detailed coseismic slip of the two events. Coseismic modeling reveals that the January and March 2022 earthquakes ruptured two buried west-dipping moderate-angle and high-angle right-lateral strike-slip faults, respectively. Most of the slip of the January event occurred at depths from 1.7–7.6 km, while the majority of the slip associated with the March event occurred at depths from 2.5–10 km, which may have been restricted by the intersections between the January and March Hala Lake seismogenic faults. By a comprehensive analysis of the coseismic inversions, stress changes, and early postseismic signal, we suggest that the significant fault dip difference (~30°), highlighting a fault segmentation, stops the rupture propagation from one fault segment to another and that fluid migration may encourage the restart of the rupture of the later event, which requires further investigation. Moreover, Coulomb stress modeling shows stress loading on the eastern segment of the Daxueshan–Shule Fault and the northern segment of the Elashan fault, which we should pay more attention to.

Abstract On January 19, 2020, an M w 6.0 earthquake occurred in Jiashi, Xinjiang Uygur Autonomous Region of China. The epicenter was located at the basin-mountain boundary between the southern Tian Shan and the Tarim Basin. Interferometric Synthetic Aperture Radar (InSAR) is used to obtain the coseismic deformation field from both ascending and descending Sentinel-1A satellite images of the European Space Agency. The results showed that the coseismic deformation is distributed between the Kalping fault and the Ozgertaou fault. The earthquake produced significant deformation over an area of approximately 40 km by 30 km. The maximum and minimal displacements along the line of sight (LOS) are 5.3 cm and − 4.2 cm for the ascending interferogram and are 7.2 cm and − 3.0 cm for the descending interferogram, respectively. The fault geometry from the Multi peak Particle Swarm Optimization computation indicates that the seismogenic fault is a shallow low-dipping planar fault that is 4.58 km depth underground. The finite slip model inverted by the Steepest Descent Method implies that the rupture is dominated by a thrust fault. The slips are concentrated in a depth of 5–7 km with a maximum slip of 0.29 m. The estimated total seismic moment is 1.688 × 1018 Nm, corresponding to a magnitude of M w 6.1. The seismogenic fault is the Kalping fault which has a listric structure. The coseismic deformation only occurred on the décollement layer and did not involve the ramp segment. The coseismic Coulomb stress changes have enhanced the stress on the deep margin of the Jiashi earthquake rupture area, indicating that there is still the possibility of strong earthquakes in this region in the future.

The interconnection between anthropogenic and natural surface loads and seismicity continues to be poorly understood. The metropolitan Salt Lake City in Utah hosts various industrial, hydrological, and tectonic processes, including the Bingham Canyon mine and its associated tailings facility, precipitation and water storage at the surface and in aquifers, as well as the seismically active Wasatch Fault Zone. The March 18, 2020 M5.7 Magna earthquake occurred east of a mine tailings impoundment that receives ∼60 million tons/yr of ore waste products since the early 1900s. Here we investigate the spatiotemporal elastic stress changes due to anthropogenic mass transfer and natural hydrological loading and unloading. Two local earthquake clusters host persistent microseismicity and the 2020 M5.7 Magna earthquake sequence. The amplitude and sign of the computed Coulomb stress changes at seismogenic depths strongly vary with the receiver fault geometry, the frictional coefficient, and the location, and can reach tens of kPa and ∼1 kPa/yr due to the tailings loads, a substantial fraction of background tectonic loading. The long‐term and seasonal stress changes from regional hydrological processes are only up to a few kPa. A lack of statistically significant seasonality in seismicity across Utah suggests a weak control by cyclic hydrological loads. Explicit knowledge of the fault architecture is essential to allow for seismic hazard assessment considering external stress loading. Plain Language Summary: The anthropogenic surface modifications in naturally hazardous environments have received relatively little attention due to their small dimensions and shallow locations. We note a compelling spatial correlation between a mine tailings impoundment and the March 18, 2020 M5.7 Magna earthquake, its aftershocks, and persistent earthquake clusters in the Salt Lake City region. This highly populated region hosts various industrial, hydrological, and tectonic processes. Here we characterize the spatiotemporal stress changes since the early 1900s due to the industrial and hydrological sources. The modeled elastic stress changes in the three dimensional subsurface vary in sign and magnitude, depending on the location, geometry, and frictional properties of active faults. Comprehensive characterization of fault architecture and seismic monitoring near sites of industrial production is warranted in critical geological and tectonic settings to ensure socioeconomic health and sustainable development. Key Points: The M5.7 Magna earthquake and its aftershocks, as well as persistent historical seismicity occurred in two clustersThe elastic stresses near the hypocenter produced by nearby industrial loads exceed those from hydrological sources by two orders of magnitudeThe magnitude and sign of loading stresses resolved on receiver faults are sensitive to fault geometry, frictional coefficient, and location [ABSTRACT FROM AUTHOR]

The East Anatolian Fault Zone (EAFZ) with an average length of 500 km is one of the most seismically active regions of Turkey, and many major earthquakes have occurred along this fault zone. The earthquake of 24 January 2020 (Mw = 6.8) with the epicenter in Sivrice (Elazığ) occurred on the EAFZ and caused loss of life and property. This study was carried out to investigate the Coulomb stress changes before and after the Sivrice mainshock by using 89 earthquakes (M ≥ 4.5) with different depth ranges (7.5, 15, 22.5, 30 km) that occurred in the EAFZ between 1997 and 2020. Coulomb stress change maps were created using the Sivrice (Elazığ) mainshock and subsequent earthquakes. The maps showed that the stress continued in the northeast and southwest directions and caused a positive Coulomb stress change. According to the Conrad discontinuity depth calculation obtained from the thermal investigation covering the EAFZ and its immediate surroundings, a value of 21.2 km was obtained. While there was no stress increase at depths deeper than 20 km before the Sivrice mainshock, there was a stress increase up to 30 km after the mainshock. Rigidity of crustal structure is higher between segments 1 and 5 compared to segment 6 according to results of Curie Point Depth (CPD) on the EAFZ. This induced the positive Coulomb stress change along with the fault segments at the deeper depth levels. The high Coulomb stress values were especially observed around the Palu-Hazar Lake and Çelikhan-Gölbaşı segments. Therefore, these segments were defined as the earthquake hazard potential region. [ABSTRACT FROM AUTHOR]

On 8 January 2022, a Moment Magnitude (Mw) 6.7 earthquake occurred in Menyuan, China. The epicenter was located in the western segment of the Lenglongling fault of the Qilian-Haiyuan fault zone. In this area, the Mw 5.9 Menyuan earthquake on 26 August 1986 and the Mw 5.9 Menyuan earthquake on 21 January 2016 successively occurred. The seismogenic structures of the 1986 and 2016 earthquakes are on the Northern Lenglongling fault, which is a few kilometers away from the Lenglongling fault. After the 2022 Menyuan earthquake, we collected GF-7 and Sentinel-1 satellite images to measure the surface deformation of the earthquake sequence. Based on the elastic dislocation theory, the fault model and fault slip distribution of the 2016 and 2022 Mengyuan earthquakes were inverted using coseismic surface displacements. The results show that the 2016 event is a reverse event, with the maximum coseismic surface displacement on LOS reaching 8 cm. The strike, dip, and rake of the earthquake rupture were 139°, 41°, and 78°, with the maximum slip reaching 0.6 m at a depth of 8 km. The surface rupture of the 2022 Mw 6.7 earthquake ran in the WNW–ESE direction with a maximum displacement on LOS of 72 cm. The main seismogenic fault of the 2022 event was the western segment of the Lenglongling fault. The strike, dip, and rake of the rupture were 112°, 85°, and 3°, with the maximum slip reaching 4 m at a depth of 4 km. The Coulomb failure stress change shows that the earthquake sequence generated a considerable positive Coulomb failure stress of more than 2 bar. These observations suggest that the earthquake sequence around Menyuan is mainly governed by the activities of the Lenglongling fault around the northeastern Tibetan Plateau. In addition, their sequential occurrences could be related to earthquake-triggering mechanisms due to stress interaction on different deforming faults. Thus, the Lenglongling fault has received a great amount of attention regarding its potential earthquake hazards.

Abstract The Ning'er Mw 6.1 earthquake on 3 June 2007 occurred in the southwest to the Sichuan‐Yunnan rhombic block with complicated seismic structures. The focal depth determined by the U.S. Geological Survey is only 5 km, but the field investigation did not find obvious surface ruptures in the epicenter area. The magnitude obtained by inverting the broadband waveforms is Mw 6.4 that is much larger than the Mw 6.1 calculated by U.S. Geological Survey, indicating this event is complicated. The Interferometric Synthetic Aperture Radar is used to study the fault geometry, coseismic slip model, and Coulomb stress changes around the seismic region. It shows that this event is mainly dominated by a right‐lateral strike‐slip fault with a slight thrust component. The fault plane is 28‐km long along the strike and 14‐km wide along the dip. The maximum slip is up to 1.02 m at a depth of 3.6 km and the released moment is 2.57 × 1018 Nm, corresponding to a magnitude of Mw 6.25. The shallow source of this event is related to inelastic off‐fault deformations along the fault or magma chamber. The lack of obvious surface ruptures indicates the strain is not completely released. The coseismic Coulomb stress changes suggest this earthquake has enhanced the stress on the Puwen fault and Mohei fault. The future seismic risks of these two faults and its adjacent regions cannot be ignored since aftershocks are fewer and the residual strain unreleased by the Ning'er event.

The earthquake (ML5.2) occurred at Chushan town, Nantou on Nov.11, 2017 and had caused a lot of aftershocks around the hypocenter of the mainshock. The Coulomb stress changes (ΔCFSs) by the mainshock demonstrated most of the aftershocks located within the positive parts greater than 0.1 bar, revealing the aftershocks may be induced by the mainshock. After investigating the ΔCFSs at different depths, the results showed most of positive parts of ΔCFSs under depth 15km were transferred to the southeast and southwest regions. About ten days later, there were lots of earthquakes (ML 5.2~3) with depth below 15km clustered exactly in the southeast region. The southwest region nears the Meishan fault, which began as a reverse thrust slip and caused large earthquake with ML 7.0 before 110 years ago. This means the Meishan fault may be triggered by the successive earthquakes near the fault. Based on the seismic spectrum intensities, the seismic hazards by the potential Meishan earthquake are estimated. The maximal seismic intensities will occur at Chushan town and the segment of freeway 3 connects Nantou city and Chushan town have to pay more attentions. The landslides may happen at the junctions of Nantou and Yunlin counties, which great landslides had happened, when Chi-Chi earthquake (ML7.3) occurred in 1999. [ABSTRACT FROM AUTHOR]

The gravitational pulls from the moon and the sun result in tidal forces which influence both Earth's solid and water mass. These stresses are periodically added to the tectonic ones and may become sufficient for initiating rupture in fault systems critically close to failure. Previous research indicates correlations between increased seismicity rates and low tides for fast‐ and intermediate‐spreading mid‐ocean ridges in the Pacific Ocean. Here, we present a microseismicity data set (4,719 events) recorded by an ocean bottom seismometer deployment at the equatorial Mid‐Atlantic Ridge. We show that low, as well as decreasing ocean water level, result in relatively elevated seismicity rates at higher magnitudes (lower b‐values), translated into increased probabilities of stronger event occurrence at or towards low tides. Moreover, seismic bursts (enhanced activity rate clusters), occurring at rates well above the reference seismicity, are exclusively present during values of either high tidally induced extensional stresses or high extensional stress rates. Although the b‐value differences are not significant enough to be conclusive, the seismicity rate variations exhibit statistical significance, supporting the previous findings for tidal triggering at low tides within normal‐faulting regimes and extending the range of observations to slow‐spreading ridges. Observed triggering of slip on low angle faults at low tides is predicted by Coulomb stress modeling. The triggering of slip on high angle faults observed here, is not easily explained without another factor. It may be related to the presence of a shallow magma body beneath the ridge, as supported by previous seismic imaging in the region. Plain Language Summary: The Earth is periodically subjected to tidal forces due to the combined influence of solar and lunar gravity. Solid Earth tides dominate in the continents, whereas in particular marine sites ocean tides are strong enough to generate considerable stress. Although theoretically plausible, tidal triggering of earthquakes has been only occasionally observed in the Pacific Ocean, with the results often being controversial. The deployment of ocean bottom seismometers (OBS) in combination with modern earthquake detection techniques, offer better chances to study the remote oceanic environments, making it possible to recognize a tidal footprint on small earthquakes. Here we present a dense data set of small earthquakes from the equatorial Mid‐Atlantic Ridge, recorded by a temporary OBS network operated from March 2016 to February 2017. We find that the majority of the earthquakes occurred during or towards low tides, corresponding to high extensional stressing. We show that seismicity bursts (very high activity rates) exclusively occur at low tides. There is also evidence that a larger proportion of stronger events occur during or just before low tides. We interpret our results in terms of stress change modeling, considering faulting properties and the potential existence of a magma chamber beneath the study area. Key Points: Tidal triggering is investigated for a microseismicity data set from the equatorial Mid‐Atlantic RidgeSeismicity rates are increased and b‐values are decreased during and towards low tidesCoulomb stress modeling suggests additional factors are required, for example, a shallow magma chamber beneath the ridge [ABSTRACT FROM AUTHOR]

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