Coulomb stress change (ΔCFS) is widely used to evaluate static earthquake triggering, yet threshold-based triggering statistics can be sensitive to assumptions about fault friction, including possible fluid-related weakening, and to hypocentral uncertainty. Using the 2024 Noto MW7.5 earthquake sequence, we compute static ΔCFS for (i) the MW5.5 foreshock acting on the MW7.5 mainshock receiver plane and (ii) the mainshock acting on early aftershocks within the first 51.5 h. To represent plausible time-varying fault strength potentially influenced by fluids, we convert a friction scenario μ(t) into effective friction μ′(t) under isotropic poroelastic relations for two upper-crustal end members, and evaluate ΔCFS at each aftershock’s reported hypocentral longitude, latitude, and depth. The foreshock yields positive ΔCFS on nodal plane II of the mainshock ( 0.02 – 0.03 MPa for μ′ = 0.17 – 0.25), exceeding the commonly used 0.01 MPa benchmark. For 2,982 aftershocks, the fractions with ΔCFS ≥ 0.01 MPa are 39 – 46

Following the Wenchuan MS8.0 earthquake, numerous studies have sought to determine the sliding friction coefficient of the Longmenshan fault (LMSF) zone. However, results have varied widely (0.02–0.61), deviating significantly from traditional understandings (0.6–0.85). As a critical parameter governing fault strength, the sliding friction coefficient influences coseismic stress drop and the recurrence interval of large earthquakes. To better constrain this coefficient, we constructed a two-dimensional finite-element contact model extending 300 km in length and 104 km in depth that includes the LMSF. Constrained by GPS observations, we controlled fault activity using static and dynamic friction constitutive relations, and conducted multiple numerical simulations by assigning different sliding friction coefficients to the fault to simulate regional deformation and the recurrence of strong earthquakes. Comparison between the simulation results and observational data, along with lateral comparisons across different simulation results, allowed us to constrain the sliding friction coefficient of the LMSF. The main conclusions are as follows: the LMSF exhibits a relatively low sliding friction coefficient around 0.08. The recurrence interval for magnitude 8.0 earthquakes on the LMSF is approximately 5,460 ± 130 years. Coseismic shear stress drop is a key factor in controlling the spatial distribution of mainshocks and aftershocks. Additionally, the rapid uplift along the eastern Qinghai-Xizang Plateau is likely driven by upper mantle creep beneath the Songpan–Garzê block.

Earthquake focal mechanisms provide essential constraints on the stress state of the Earth's crust. Conventional stress tensor inversion relies on fitting slip directions on multiple faults, but because double-couple focal mechanisms can also be represented by the orientations of P and T axes, such inversions effectively fit the spatial distribution of these axes. This study examines whether the distribution patterns of P and T axes alone can directly constrain the crustal stress tensor. We perform modeling experiments that simulate fault instability and slip under a range of stress states and fault failure criteria. The results show that systematic changes in stress conditions produce distinct and predictable transitions in P and T axes distributions. The geometric centers of clustered axes correspond to the orientations of the principal stress axes. A clustered P axis distribution combined with a circular Taxis pattern indicates comparable magnitudes of sigma 2 and sigma 3, whereas a clustered T axis distribution with a circular P axis pattern does not require and to be similar in magnitude. Randomly intermingled P and T axes distributions do not occur in the simulations, indicating that such patterns observed in real data likely reflect stress heterogeneity or inaccuracies in focal mechanism solutions. These conclusions are validated using real fault-slip data and earthquake focal mechanisms. The results provide a practical framework for diagnosing stress heterogeneity, evaluating data quality, and anticipating the reliability of stress inversion outcomes.

[Objective]The Dingri area in Xizang is located within the Lhasa Block of the Qinghai-Xizang Plateau.It belongs to the core region of the Southern Tibetan Rift System and is a key zone with high seismic activity and earthquake potential.The M 6.8 earthquake that struck Dingri,Xizang(28.50°N,87.45°E)on January 7,2025,was the largest ever recorded in this area.Although previous studies have clarified the seismogenic structure and rupture distribution of this earthquake,few studies have addressed its impact on the surrounding areas.Therefore,this study calculates the co-seismic displacement and horizontal strain fields generated by the earthquake and the changes in Coulomb failure stress induced on surrounding faults.The study identifies high-risk fault segments and provides a scientific basis for regional seismic hazard assessment,monitoring,and early warning.[Methods]The local stress field was projected onto two potential nodal planes of the earthquake determined by the central focal mechanism solution;Nodal Plane I(strike 184.37°,dip 47.67°,rake-78.10°)was found to be more prone to rupture.This plane was identified as the seismogenic fault plane when combined with the strike of the local fault.Then,based on the seismic rupture model and the homogeneous elastic half-space model,the co-seismic surface displacement field and the horizontal strain field were calculated.Furthermore,according to the data on the geometry and slip properties of faults near the epicenter,the study systematically quantified the impact of the earthquake on the Coulomb stress of major surrounding faults.[Results]In terms of horizontal displacement,the materials on the east and west sides of the epicenter moved outward,while materials in some northern areas converged toward the epicenter,with a maximum horizontal displacement of 76.65 cm.In terms of vertical displacement,subsidence occurred on the north side of the epicenter(with a maximum of 83.97 cm)and uplift occurred on the northeast side(with a maximum of 33.25 cm),showing an obvious normal fault mechanism near the seismogenic fault.Volumetric strain and areal strain exhibited consistent distribution patterns;both exhibited tension on the north and south sides of the epicenter(with maxima of 1.768×10-6 and 1.737×10-6,respectively)and compression around the epicenter as well as on the east and west sides(with maxima of 1.874×10-6 and 1.987×10-6,respectively).Coulomb failure stress induced by this earthquake on the major surrounding faults at a depth of 10 km showed that the Dengmecuo Fault experienced significant stress unloading.This was the most intense stress release among all faults,effectively releasing regional tectonic stress and confirming that the Dengmecuo Fault is the seismogenic fault.The maximum Coulomb stress increment of the southern segment of the Shenza-Dingjie Fault was 0.0349 MPa,and that of the eastern segment of the Lazi-Qiongdoujiang Fault was 0.0191 MPa.Both exceeded the triggering threshold of 0.01 MPa,indicating high seismic hazard.[Conclusions]The study shows that this earthquake was a normal-faulting earthquake under the regional tectonic stress field and the Dengmecuo Fault was the seismogenic structure.Significant changes occurred in the co-seismic displacement field and the horizontal strain field around the epicenter.The Coulomb stress increments of the southern segment of the Shenza-Dingjie Fault and the eastern segment of the Lazi-Qiongdoujiang Fault exceeded the triggering threshold,indicating that moderate to strong earthquakes are possible in these segments in the future,which requires high attention.[Significance]By analyzing the impact of the January 7,2025,M 6.8 Dingri earthquake in Xizang on the Coulomb stress of major faults in southern Xizang,this study identified the high-risk fault segments that need focused attention,providing a valuable reference for subsequent seismic monitoring and early warning.

We investigated the influence of historical earthquakes on the 2022 Luding MS6.8 earthquake and its subsequent effects. We computed the viscoelastic Coulomb stress changes induced by these historical seismic events using the rupture model of historical earthquakes and the layered Maxwell viscoelastic medium model. Our findings indicate that the Luding earthquake was brought forward approximately 29 years because of several historical earthquakes. Specifically, the 1923 Renda MS7.3 earthquake, the 1933 Diexi MS7.5 earthquake, the 1973 Luhuo MS7.3 earthquake, the 2008 Kangding MS5.1 earthquake, the 2008 Wenchuan MS8.0 earthquake, the 2014 Kangding MS6.3 earthquake, and the 2014 Kangding MS5.8 earthquake advanced the occurrence of the event by 117.61, 26.67, 84.51, 0.27, 0.91, 7.64, and 3.17 years, respectively. Conversely, the 1936 Mabian earthquake swarm, the 1948 Litang MS7.3 earthquake, the 1955 Kangding MS7.5 earthquake, and the 2013 Lushan MS7.0 earthquake delayed its occurrence by 39.89, 22.43, 144.23, and 4.89 years, respectively. Furthermore, by employing the half-space homogeneous elastic model and the rupture characteristics of the Luding earthquake, we computed the coseismic Coulomb stress changes in neighboring faults. Our results reveal increased Coulomb stress on the Xianshuihe fault (excluding its southern segment), the Anninghe fault, the Zemuhe fault, the Daliangshan fault, the southern segment of the Longmenshan fault, the northern segment of the Mabian-Yanjin fault, and the Xiaojinhe fault. Conversely, we observed stress decreases in the southern segment of the Jinshajiang fault, the central and eastern segments of the Longriba fault, the Mabian-Yanjin fault (excluding its northern segment), and the southern segment of the Xianshuihe fault.

Sediment thickness is an important reference for evaluating the site effects of seismic waves and a critical indicator for assessing seismic disaster losses. Based on the Horizontal-to-Vertical Spectral Ratio method (HVSR), this study calculates sediment thickness and evaluates site effects using nearly one year of ambient noise data recorded by a dense seismic array in the Guye seismic source zone. The results show that the sediment thickness in the study area ranges from 0 to 450 m, with a significant difference between the eastern and western parts. The site amplification factor varies from 1.0 to 14.0. The site vulnerability index exhibits a spatial pattern of high values in the west and low values in the east. The western zone with thick sediments has a high risk level of 60–110, indicating a high seismic risk region for building damage. This study further reveals that the 2020 M s 5.1 Guye earthquake occurred in the thin-sediment zone in the northern Tangshan Fault zone. Stress diffused along the fault after the 1976 event and concentrated in the thin-sediment area to drive this earthquake. The pronounced site effects in this region further intensify the ground motion intensity. The synergistic coupling between the strong seismic source input from fault activity and site effects gives rise to anomalous ground motion, thus forming an anomalous seismic damage zone. The results of this study can provide a scientific basis for regional seismic hazard risk assessment, engineering seismic fortification, and earthquake prevention and disaster mitigation.

In this study, by analyzing the dynamic changes in the friction coefficient, the evolution patterns of fluids at different times and depths and their effects on earthquake occurrence in the northeastern Noto Peninsula are elucidated. The results show that the existence of fluids reduces the friction coefficient of faults and affects seismicity, especially during the 2023 MW6.5 earthquake and 2024 MW7.5 earthquake. In addition, on the basis of seismic data and geochemical evidence, fluid may have originated in the mantle through ancient magma channels. The fluid infiltrates into the upper crust and accumulates in the fault system. The accumulated fluid led to the occurrence of the MW7.5 earthquake. After that, the fluid gradually migrated to 0-6 km along the fault and drained through the fault to the surface. A significant increase in the shallow (0-27 km) friction coefficient after the earthquake indicates that the role of the fluid gradually weakened.

To investigate the relationship between the stress regime and the type of focal mechanism solution,we employ the three-dimensional stress Mohr circle to analyze the influence of the instability coefficient value ofsliding fault on the type of focal mechanism solution. The generated focal mechanism solution types and theirinfluencing factors under the action of three typical stress regimes are obtained. The following conclusions aredrawn: (1) When the instability coefficient for fault sliding approaches 1 (the range of fault instability coefficientis 0 similar to 1, where 0 indicates the most difficult to slip and 1 indicates the easiest to slip), the stress regimes ofstrike-slip faulting, normal faulting, and thrust faulting mainly generated focal mechanism solutions consistentwith their respective properties. When the instability coefficient is lower than 1, focal mechanism solutionsdifferent from the stress regime can be generated. It can be observed that the lower instability coefficients forfault slip, the more focal mechanism solution types generated by various stress fields. Types of focal mechanismsolution generated by different stress field types are not only controlled by the stress regime but also influencedby the fault instability coefficient required for fault slip. (2) The types of focal mechanism solution are mainlycontrolled by stress field types and fault parameters, but the stress ratio, friction coefficient, pore pressure andshear strength of fault have some influence on the generated focal mechanism solution types. (3) The stress ratiosignificantly impacts the instability coefficient of faults with varying parameters. However, it has minimal effecton the overall distribution characteristics of the instability coefficient with the strike and dip angle underdifferent stress regime. The fault parameters in the center of the high value area of the instability coefficient aredetermined by the specific stress field parameters and the friction coefficient. This study can provide referencefor the study of the diversity of focal mechanism solutions, the uniformity of stress field, the friction strength andthe pore pressure

To investigate the seismic hazards caused by large earthquakes around the Three Gorges Reservoir (TGR), we calculate the postseismic quasistatic Coulomb failure stress (CFS) and the coseismic dynamic changes in the CFS generated by the Wenchuan earthquake (WCE, mainshock) on May 12, 2008(WCE), in the TGR area. For the coseismic dynamic CFS changes, the results show that in the first few minutes after the WCE, the seismic waves spread to the Xiangxi earthquake (XXE) area in the Xiannvshan fault (XNF) zone on November 22, 2008.The dynamic change in the CFS generated in the XNF zone was positive, with a peak value of 1.32MPa. This result indicates that the coseismic dynamic change in the CFS generated by the WCE made the rocks in the XNF zone more susceptible to fracturing and weakening, which may have triggered the XXE in the TGR. The results reveal that the postseismic quasistatic CFS changes were positive and increased with depth, reaching approximately 0.05 KPa at the epicenter before the XXE, resulting in the quasistatic change in the CFS generated by the WCE on the XNF surface. The postearthquake quasistatic change in the CFS exhibited a small positive value, indicating that shear stress had been continuously applied on the fault plane to promote sliding of the fault plane, which may have had a certain impact on the fault rupture. This study has practical importance for analyzing the seismic hazards of large earthquakes near the TGR and the earthquake resistance and defense of the TGR area.

Stress field inversion based on focal mechanisms requires accurate identification of seismogenic faults from the two nodal planes given by the focal mechanism, and then obtaining the stress field by fitting the slip direction of the seismogenic faults. However, current techniques and methods cannot guarantee that seismogenic faults can be accurately identified from all focal mechanisms. Therefore, a small fraction of the auxiliary fault planes are included in the fault data used for stress field inversion, and to what extent does the presence of this fraction of pseudo faults cause the reconstructed stress field to deviate from the actual stress field? In this paper, we have shown through synthetic experiments that the incorrect selection of faults for part of the focal mechanisms may cause the reconstructed stress direction and the relative magnitude of the principal stresses ( R) to deviate significantly from the actual situation. The amount of deviation in the reconstructed stress field is mainly related to three factors, which are the actual stress R value, the fraction of focal mechanisms that incorrectly selected faults, and the noise level contained in the focal mechanisms. When the actual stress R value is around the median, the only way to accurately reconstruct the R value is to accurately select the fault planes. When the actual stress R value is relatively small, accurate selection of the fault plane helps to accurately reconstruct the stress orientation. Therefore, accurate selection of faults from the focal mechanisms can ensure that the orientation and R value of the stress field can be accurately reconstructed under different background stress fields, which is important for reasonable interpretation of tectonic movement based on the reconstructed stress field.

The 2021 Maduo earthquake sequence occurred on the Jiangcuo fault zone in Qinghai, China. However, the earthquake sequence did not occur along a straight fault. Aftershocks in the southeast section deflected the aftershocks in the southeast section to the east, when the aftershocks in the northwest section bifurcated. To investigate the relationship between these eastward deflections, aftershock bifurcations, and fault activity, 150 focal mechanism solutions of the Maduo earthquake sequence are collected and processed, and then the stress fields in the subregion and whole region are subsequently determined by partitioning the sliding window from southeast to northwest. The results show that the overall tectonic stress field of the Maduo earthquake sequence exhibits northeast -southwest compression and northwest -southeast extension due to the northward compression of the Indian plate, causing rupture of the Kunlunshankou-Jiangcuo fault, which straightened the curved Maduo-Gander fault. The stress field at the deflection of the southeastern section of the source area differs significantly from the overall stress field. The plunge angle of the extensional stress axis in the southeastern deflection area is close to vertical, which is speculated to be due to the effect of the crack tip and the adjustment of local stress after the earthquake. The extensional stress axis at the bifurcated distribution of aftershocks in the northwestern section of the source area is slightly greater than of the overall stress field, indicating that the activation of the bifurcated hidden fault was triggered by the high rupture intensity and the adjustment of local stress. The reactivation of the hidden bifurcated fault results in local stress and causes decreasing seismicity west of the bifurcation area.

The current stress tensor inversion method based on the focal mechanism cannot solve problems such as the interference of too many outliers on the results and the slow speed and low accuracy caused by the excessive computation of the inversion process; therefore, we propose a new stress tensor inversion method, GSBBO (grid search, boxplot and Bayesian optimization), which combines machine learning algorithms to sieve out outlier data and improve the inversion speed and accuracy. The method first screens the focal mechanism data via a grid search and boxplot, and this process eliminates the bias of the outliers on the results. Then, to improve the speed and accuracy of the inversion results, the method further inverts the stress tensor by means of Bayesian optimization, which can obtain high-precision results quickly by means of screened datasets and machine learning algorithms. The GSBBO method is validated using artificially synthesized focal mechanism data containing random noise and outliers for three stress systems. The obtained results are compared with those of grid search and Bayesian optimization, and the GSBBO method is able to accurately identify the outliers and provide more accurate results quickly. Applying the method to the area of the Great Wall Station in Antarctica, the results show that the area experiences near-vertical compressive stress and strong northwest‒southeast extensional stress, which is consistent with the extensional stress in the area due to the subsidence of the Phoenix Plate. These findings indicate the continuing subsidence process of the Phoenix Plate in Antarctica.

Two M(w)7 earthquakes occurred near the East Anatolia fault (EAF) in southeast region of Turkey in 2023. Distribution and focal mechanism of a large number of occurred aftershocks provide a good foundation for estimating the fault geometry and regional stress field. in the southeast segments of the EAF. In this study, the refined positioning result of the aftershocks of the earthquake sequence is collected, the geometry parameters of the 8 sub faults in 8 clustering zones are estimated by using the method of fuzzy clustering and fault plane estimating. The results show that the 4 steep sub faults of the M(w)7.8 earthquake are dipping to the northwest, which consistent with the dip of the northeast section of the EAF; the main fault area of the M(w)7. 6 earthquake is dip to the north, with 2 opposite dip direction and NE. NNE azimuth sub faults at the west end and 1 dipping opposite to the EAF and NE azimuth sub fault at the east end. Then the earthquake focal mechanism around the Turkey double strong earthquakes was collected, and the stress field at each sub region was calculated. It is found that the northeastern rupture region of the M(w)7.8 earthquake presents the strike slip stress state with NE SW compression and NW SE extension, which shows the strike slip movement of EAF caused by the oblique pushing of the Arabian plate against the Anatolia plate. The southwest rupture zone of the M(w)7.8 is characterized by east west stretching and south upward or north downward extrusion processes. It is located at the triple junction of the Arabian Plate, the African plate and the Anatolian block. in which the stress state reflects the EW stretching state caused by the northward pushing of the African and Arabian plates and the forced westward migration of the Anatolian block. The stress. field of the M(w)7.6 earthquake rupture zone, which located in the Anatolian block, is characterized by the process of near NS extrusion and west downward extension, which reflecting the pushing action of the Arabian plate and the African plate and the westward extension of the block. The stress field of the main area of the earthquake rupture is projected to the nodal planes of the central focal mechanism of the two earthquakes. It is found that the stress release direction of the M(w)7.8 earthquake is consistent with the direction of the tectonic stress field, while the stress release direction of the M(w)7. 6 earthquake is quite different from that of the tectonic stress field, indicating that M(w)7.6 may be triggered by the M(w)7. 8 earthquake.

The 20 March 2020 Dingri M(w)5.6 earthquake occurred in the southwestern margin of the Tibetan Plateau, about 250 km away from the 2015 Nepal M(W)7.9 earthquake. Whether the Nepal earthquake, especially the afterslip, triggered the Dingri earthquake remains to be studied. Here, Interferometric Synthetic Aperture Radar (InSAR) and regional seismic data were combined to learn about the rupture features of the Dingri earthquake. We first utilized the near-field displacements together with broadband seismic waveforms to reveal the uniform slip model by using a Bayesian bootstrap optimization nonlinear inversion method. Then, we constructed a fault plane based on the geometrical parameters and inverted the source slip distribution. The study found that the strike of the Dingri earthquake's fault was similar to 334 degrees and the dip was similar to 51 degrees. The rupture range was similar to 5.6 kmx4.4 km, and the total seismic moment released was similar to 3.33x 10(17) N center dot m, corresponding to M(W)5.6. The peak slip was similar to 1.27 m, which occurred at a depth of similar to 3.786 km. The slip was mainly confined between similar to 2.0 and 5.5 km in depth and was characterized predominantly by normal slip with slight right-lateral strike-slip components, which suggest that the Indian plate compresses the Eurasian plate northeastward, which produces near East-West tension in southern Tibetan Plateau. The study of Coulomb stress change showed that the Nepal M(W)7.9 earthquake and its aftershocks, together with four historical earthquakes in Dingri area, triggered the 2020 Dingri M(W)5.6 earthquake. The Coulomb stress change caused by afterslip in two years of the Nepal earthquake accounts for similar to 40% the total Coulomb stress increase, which indicates that the role of the afterslip in seismic risk assessment cannot be ignored.

This study investigates the impact of the magnitude 6.9 Menyuan earthquake in Qinghai, 2022, on surrounding areas using the elastic half-space dislocation model. It calculates the co-seismic displacement and stress fields of the Menyuan earthquake and examines the mainshock's triggering effect on aftershocks based on co-seismic Coulomb stress changes. The results show: (1) The materials converge from the southwest and northeast before dispersing from the northwest and southeast around the epicenter, with subsidence in the southwest and northeast and uplift in the northwest and southeast. (2) Stress-wise, expansion occurs southwest and northeast, while compression occurs northwest and southeast of the epicenter. (3) The Coulomb stress change displays positive and negative areas. At a depth of 5 km, the aftershock triggering ratio of magnitude 3 and above is 33.33

Since the occurrence of the Tangshan MS7.8 earthquake, Guye—Luanxian area has been a frequently occurrence of aftershocks. The fault and geological structure are very complex in Guye—Luanxian area. What are the differences in the fragmentation degree of these faults? The problems are concerned by seismologists. To answer these questions, by using the waveform records of the mobile seismic network densely deployed in the Guye—Luanxian area from August 2020 to July 2021, we study the anisotropy of the upper crust in Guye—Luanxian area according to the principle of shear wave splitting. The following conclusions are obtained: (1) The average polarization direction of fast shear wave in Guye—Luanxian area is NE86.2°±27.8°, the average time delay of slow shear wave in this area is 2.37±1.25 ms·km-1. The first dominant polarization direction of fast shear wave is ENE, which is consistent with the direction of principal compressive stress of regional background, the second dominant direction is NE direction, which reveals the tectonic significance that the faults in this area are mainly developed in NE direction. (2) The polarization direction of fast shear wave near the Tangshan fault zone shows the second dominant direction in NE direction, which is consistent with the fault strike. The time delay of slow shear wave of stations near the fault is higher, and the difference of time delay in stations is smaller, which indicates that the regional anisotropy is stronger, and the fragmentation degree along the NE direction is stronger and homogeneity. (3) The polarization direction of fast shear wave near Luanxian—Leting fault and Lulong fault shows complexity, indicating that the intersection of two active faults produces a complex crustal fracture structure in the crust. The time delay of slow shear wave in stations near the fault is higher, and the time delay difference of each station is larger, which indicates that the regional anisotropy and fragmentation degree are stronger, and the fragmentation is heterogeneity. (4) The polarization direction of fast shear wave at stations near the Fengtai—Yejituo fault and Zhenzizhen fault is consistent with the direction of regional principal compressive stress. The slow shear wave time delay of stations near the fault is the smallest, indicating that the Fengtai—Yejituo fault and Zhenzizhen fault have no influence on the polarization direction of fast shear wave at nearby stations, regional anisotropy and fragmentation degree are weaker, and may be indicating closure of fracture internal cracks in the faults. Moreover, we also discussed whether the tip effect on the Tangshan fault after the 1976 Tangshan MS7.8 earthquake has an impact on the stress field in the northern segment of the Tangshan fault zone. The results of this study not only reflect the relationship between the complexity of fault distribution and crustal anisotropy, but also reveal the difference of crustal anisotropy on faults with different degrees of fragmentation.

Two destructive earthquake with magnitude greater than 7.0 occurred in Türkiye on February 6,2023.So far,there are still large differences in the seismic rupture models of Türkiye obtained with different observations.Among them,the finite fault model given by United States Geological Survey is the most accurate comprehensive model available at present.Therefore,by adopting the finite fault model from the USGS as the prior model,we invert thecoseismic rupture distribution of twins strong earthquakes inTürkiye,by using the InSAR observation data from Sentinel-1.Our results reveal that:(1)The total seismic moment obtained from the inversion is 1.626 8×1021 N∙m,which is equivalent to a large earthquake with a magnitude of Mw8.1;(2)The rupture on the East Anatolian Main fault is mainly concentrated in the range of 0-15 km underground and the rupture on the Çardak-Sürgü Fault zone,but the rupture in the northern branch fault of East Anatolian fault is mostly focused in the depth range of 5-20 km.In the East Anatolian Main fault,the rupture presents two obvious high-value zones.One located at the intersection of the Narlıdağ Fault Zone and the East Anatolian Main Fault,and the other located approximately 65 km southwest of the intersection of the Narlıdağ Fault Zone and the East Anatolian Main Fault.The maximum strike-slip component of the rupture can reach 9.0 m and the maximum dip-slip component is approximately 3.0 m.In the Çardak-Sürgü Fault,the general pattern also shows two high-value zones,one located near the epicenter of the earthquake of magnitude 7.5 in Türkiye and one at the intersection of the southeast-northwest-trending and northeast-southwest-trending faults in the northwest corner of the Çardak-Sürgü Fault.The maximum value of the strike-slip component is approximately 8.1m and the maximum value of the dip-slip component is approximately 6.1 m.The rupture produced by the twin earthquake in Türkiye is dominated by the strike-slip component and supplemented by the dip-slip component.Furthermore,the twin seismogenic faults,the East Anatolian Main fault and Çardak-Sürgü Fault zone,are both generally sinistral slip in nature.However,it alsoshows there are some thrust slip and normal slip in nature on a local scale.

There were two earthquakes of magnitude 6.0 or higher that occurred in Lushan region in 2013 and 2022. The present study the geometrical parameters and slip characteristics of the seismogenic faults associated with both of the two Lushan earthquakes, based on the collected aftershock sequences, Additionally, the stress influence of the Wenchuan earthquake and the 2013 Lushan earthquake on the 2022 Lushan earthquake was analyzed. The following conclusions are obtained: (1) The fuzzy clustering method was used to estimate the location, strike and dip angle of the 5 seismogenic fault planes in Lushan region, based on 2531 seismic events that were accurately located from the two earthquake sequences. A spatial analysis revealed that these 5 faults are distributed in a floral structure pattern. (2) After collating and calculating the 127 central focal mechanisms from this area, the tectonic stress field was determined to be a thrust type stress state with compression occurring in SEE—NWW direction and extension of nearly vertical direction. (3) By projecting the tectonic stress field onto the two seismogenic faults of the Lushan earthquakes, it was found that both of these faults are prone to reverse-faulting events. (4) The receiving fault parameters utilized for the 2022 Lushan earthquake sequence were based on the geometric parameters of its fault plane. By estimation, the stress influence of the Wenchuan earthquake and the 2013 Lushan earthquake on the 2022 Lushan earthquake were estimated. The results show that the Wenchuan earthquake promoted the activity of the seismogenic faults that triggered the Lushan earthquake sequence in 2022, while under the combined influence of the Wenchuan earthquake and the 2013 Lushan earthquake, the activity of the seismogenic faults that caused the Lushan earthquake sequence in 2022 was suppressed. Based on GPS observations of the strain rate, it was found that the combined effects of the Wenchuan earthquake and the 2013 Lushan earthquake caused a delay time of approximately 5.2~10.5 years for the occurrence of the 2022 Lushan earthquake. These studies hold significance importance for the examination of fault activity characteristics and the assessment of seismic risk in the southern segment of the Longmenshan thrust tectonic belt.

The occurrence of the 2022 Menyuan earthquake sequence provides new data for the study of the properties of the surrounding faults. In order to study the geometry of Lenglongling and Tuolaishan fault where the Menyuan earthquake sequence is located, the seismic observation data of 2022 Menyuan earthquake sequence is collected, and the precise location of 765 seismic events is accurately determined. Then, the strike and dip angle of the Lenglongling, Tuolaishan and North Lenglongling faults are estimated by using the improved fuzzy clustering method. In order to further study the slip properties of these faults, the focal mechanisms of moderate or strong earthquakes near the Lenglongling, Tuolaishan faults and their adjacent areas are collected, and the tectonic stress field in this area is determined, which shows a thrust and strike-slip stress pattern resulted from the extension of the north-eastern margin of the Tibet-plateau. Projecting the determined tectonic stress field on the Lenglongling and Tuolaishan faults, it is found that the geologic activity on the two faults shows strike-slip and thrust activity. In addition, a small number of events occurred in the North Lenglongling fault in the 2022 Menyuan earthquake sequence. In order to test whether these events were triggered by the 2022 Menyuan earthquake rupture, the Coulomb failure stress change on the North Lenglongling fault caused by the 2022 Menyuan earthquake was calculated, it is found that the Menyuan earthquake in 2022 promoted the earthquakes occurrence on the North Lenglongling fault. These studies are of significance for understanding the characteristics of fault activity and earthquake dynamics in study region.

In the 2017 Jiuzhaigou earthquake sequence, the distribution of aftershocks in the north of the main earthquake was scattered, while the distribution of aftershocks in the south of the main earthquake was linear and concentrated. The objective of this inquiry is to analyze the dynamic causes underlying such divergent patterns, relying on the horizontal strain rosette, areal strain (As), and the coefficient of accommodation (Ca) based on the regional strain rate. The following two conclusions are obtained: (1) approximately one-third of the aftershocks with focal mechanisms in the north of the main shock are thrust-type earthquakes. Because the direction of regional tectonic principal compressional strain is perpendicular to the fault trend north of the main shock, generating thrust-type earthquakes on low dip-angle faults is indeed easy. Simultaneously, the overall thrust-type focal mechanism north of the main shock and the poor consistency between plate tectonic movement and fault movement caused by the seismic sequence lead to substantial scattered aftershocks in the north of the main shock. (2) One of the aftershocks with focal mechanisms in the south of the main shock is a reverse strikeslip type, while the other 30 are strike-slip type earthquakes. Moreover, the angle between the regional tectonic principal compressional strain direction and the fault trend in the south of the main shock is large, which makes it easier for faults in the south of the main shock to produce strike-slip-type earthquakes. Simultaneously, the overall strike-slip focal mechanism in the south of the main shock, the good consistency between fault movements caused by the seismic sequence, and plate tectonic movements lead to more linear and concentrated aftershocks in the south of the main shock. The findings are significant for investigations into the seismogenic properties and activity of the Huya Fault located on the northeastern margin of Bayan Har Block.