SEISMOLOGY AND GEOLOGY

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SEISMOGENIC FAULT AND COSEISMIC SURFACE DEFORMATION OF THE DINGRI M_S6.8 EARTHQUAKE IN XIZANG, CHINA

SHI Feng, LIANG Ming-jian, LUO Quan-xing, QIAO Jun-xiang, ZHANG Da, WANG Xin, YI Wen-xing, ZHANG Jia-wei, ZHANG Ying-feng, ZHANG Hui-ping, LI Tao, LI An

SEISMOLOGY AND GEOLOGY 2025, 47 (1): 1-15. DOI: 10.3969/j.issn.0253-4967.2025.01.001

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At 09:05 am on January 7, 2025, a M_S6.8 earthquake occurred in the Dingri, Xizang, China. The earthquake caused serious casualties and property losses. Research on the seismogenic structure and characteristics of earthquake surface rupture in this earthquake is beneficial to understanding the rupture behavior and dynamic mechanism of normal-fault earthquakes. Meanwhile, it provides a basis for predicting the future strong earthquake trend of the southern Xizang rift fault system. Its epicenter is located at 87.45°E, 28.50°N, 13km depth, the China Earthquake Networks Center measures. In order to constrain the seismogenic fault and characterize the co-seismic surface ruptures of this earthquake, field investigations were conducted immediately after the earthquake, combined with analyses of the focal parameters, aftershock distribution, and InSAR inversion of this earthquake.

This preliminary study finds that the seismogenic fault of the Dingri M_S6.8 earthquake is the Dengmocuo fault, which is an active ~60km long, NS-NE-striking and normal fault. The total length of the co-seismic surface ruptures is approximately 25km, located on the north segment of the Dengmocuo fault. Meanwhile, a dense deformation zone of ground fracture with a length of ~10km is generated on the east side of Dengmocuo Lake along the contour line of the lake shore. The earthquake also induced a large number of liquefaction structures and tensional fractures in valleys and basins.

Based on along-strike discontinuity due to the development of step-overs, the coseismic surface rupture zone can be subdivided into three segments: the Gurong-Qiangga, Nixiacuo, and Yangmudingcuo segments. The surface ruptures are relatively continuous and prominent along the Nixiacuo segments. Comparatively, co-seismic surface ruptures of Gurong-Qiangga and Yangmudingcuo segments are discontinuous. The maximum of coseismic vertical displacement is roughly determined to be 2.5—3.0m based on the scarps. The width of the surface rupture zone of the Dingri earthquake can reach up to 450m in some areas. The location of surface rupture zones is not limited to fault scarps and hanging walls. There are also a large number of secondary scarps and cracks distributed in the footwall. Many cracks are distributed in an en echelon or grid pattern.

Compared to the continuous surface rupture caused by strike-slip-type earthquakes in recent years, the surface rupture of the Dingri earthquake is very discontinuous, and there is an obvious difference in displacement between each segment of the surface rupture. Preliminary speculation suggests that it may be related to the characteristics of the fault movement. Unlike strike-slip faults where the dislocation direction is parallel to the strike, the dislocation direction of normal faults is perpendicular to the strike. In addition, the observed length of surface rupture and maximum displacement of the Dingri earthquake are basically consistent with the results calculated by empirical formulations.

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SURFACE RUPTURE INTERPRETATION AND BUILDING DAMAGE ASSESSMENT OF XIZANG DINGRI M_S6.8 EARTHQUAKE ON JANUARY 7, 2025

ZOU Jun-jie, SHAO Zhi-gang, HE Hong-lin, GAO Lu, XU Yue-yi, DOU Ai-xia, LIANG Ze-yu

SEISMOLOGY AND GEOLOGY 2025, 47 (1): 16-35. DOI: 10.3969/j.issn.0253-4967.2025.01.002

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On January 7, 2025, at 9:05 AM, a 6.8-magnitude earthquake struck Dingri County, Shigatse City, Xizang, at a depth of 10km. The maximum intensity of the earthquake reached Ⅺ degrees. This study provides a comparative analysis of pre- and post-earthquake remote sensing images using GF-2 satellite data. The results identify the Dengmecuo fault as the primary seismogenic fault for the earthquake. Surface ruptures exhibit distinct geometric variations between the northern and southern segments. The northern segment, approximately 3km in length, features a relatively simple geometry with a narrow rupture width, forming a “concentrated rupture” pattern characterized by continuity. In contrast, the southern segment, approximately 12km long, displays a more complex geometry with a wider rupture width, resulting in a “diffuse rupture” pattern marked by discontinuities. Statistical analysis of building collapses and damage in 28 administrative villages near the epicenter shows that the severity of impact follows this order: Changcuo township, Cuoguo township, and Quluo township. Affected villages were classified based on their geological and geographical conditions, revealing that the earthquake's impact diminished in the following sequence: areas near the micro-epicenter, lake regions adjacent to the surface rupture zone, and bedrock mountainous areas far from the epicenter and rupture. Coseismic surface rupture analysis reveals two fault segments near Dengmecuo Lake that did not rupture. Considering the unilateral rupture pattern from south to north and the distribution of aftershocks, it is suggested that the unruptured southern segment may pose a greater seismic hazard. At a regional scale, normal faults within the fault system, including the Quluo, Dengmecuo, Guojia, and Dingjie faults, all exhibit aftershock activity. Given the recent release patterns of moderate-to-strong earthquakes, special attention should be given to the seismic risk associated with the Quluo and Dingjie faults. Finally, based on the geographical conditions, seismogenic structures, and seismic damage patterns, this study offers strategies for mitigating seismic risks in high-altitude, high-latitude regions with diverse geological and geomorphological features, diffuse fault deformation patterns, and populations of ethnic minorities.

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INVESTIGATION OF THE SEISMOGENIC STRUCTURE OF THE 2025 DINGRI M_S6.8 EARTHQUAKE IN XIZANG BASED ON THE TECTONIC STRESS FIELD PERSPECTIVE

SHENG Shu-zhong, WANG Qian-ru, LI Zhen-yue, LI Hong-xing, ZHANG Xiao-juan, GE Kun-peng, GONG Meng

SEISMOLOGY AND GEOLOGY 2025, 47 (1): 49-63. DOI: 10.3969/j.issn.0253-4967.2025.01.004

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On January 7, 2025, at 09:05 Beijing Time, an M_S6.8 earthquake struck Dingri County in Shigatse City, Xizang, as reported by the China Earthquake Networks Center. The earthquake occurred at 28.50°N, 87.45°E with a hypocentral depth of 10km, resulting in significant casualties and economic losses. In the immediate aftermath, major earthquake research institutions and seismologists, both domestic and international, promptly released the focal mechanism solution, providing crucial data for understanding the earthquake's origin and its seismogenic structure. However, the two nodal planes of the focal mechanism, derived from a double-couple source model, are equivalent, necessitating additional data or methodologies to distinguish the actual seismogenic fault plane. The parameters of the seismogenic fault are fundamental for the accurate calculation of ground motion maps, and they provide key information for seismic hazard assessment and post-earthquake rapid response guidance. Therefore, it is imperative to identify the seismogenic fault plane for the given focal mechanism solution.

This study employs the tectonic stress field in the source region of the Dingri earthquake to calculate the instability coefficients of the two nodal planes, selecting the most unstable plane as the actual seismogenic fault. This method is based on the tectonic stress field to identify the seismogenic fault plane in the two nodal planes of the focal mechanism solution. The approach is applied to identify the seismogenic fault plane of the Dingri earthquake and nearby historical seismic events.

Using the Global Centroid Moment Tensor(GCMT)focal mechanism solution, the study inverts the shallow tectonic stress field in the source region. The results reveal the maximum principal compressive stress axis is nearly vertical, and the maximum principal tensile stress axis is nearly horizontal with a strike orientation of E-W, which is a normal faulting stress regime. The stress field result is consistent with the normal faulting characteristics of the regions main fault structures.

The seismogenic fault for the Dingri 6.8 earthquake is the one-striking southward and dipping westward nodal plane of the focal mechanism solution, determined to be a normal fault. Thus, we can infer that the seismogenic fault is the Dengmocuo Fault. In addition, the identification of the seismogenic fault for the historical earthquakes in the Dingri area shows that the fault is characterized by a southward strike and westward dip, with dip angles ranging from 37° to 48°, and the fault type is normal faulting.

Identifying the seismogenic fault plane in the nodal planes of the focal mechanism solution based on the tectonic stress field, this study accurately identifies the seismogenic faults associated with the Dingri earthquake and surrounding historical events. It contributes seismological evidence for understanding the seismogenic structure of the region. It offers valuable insights for future research on seismogenic structures, particularly the determination of seismogenic faults of small and medium-magnitude earthquakes.

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STUDY ON SEISMOGENIC TECTONICS OF THE 2025 MYANMAR M_S7.9 EARTHQUAKE

XU Bin-bin, ZHANG Yi-peng, LU Le-jun, TIAN Qing-ying, YANG Xue, WANG Yang, ZHANG Pei-zhen

SEISMOLOGY AND GEOLOGY 2025, 47 (2): 649-670. DOI: 10.3969/j.issn.0253-4967.2025.02.20250089

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According to the China Earthquake Networks Center, an M_S7.9 earthquake(hereafter referred to as the Myanmar earthquake)struck the Mandalay region of Myanmar(21.85°N, 95.95°E)on March 28, 2025, at a focal depth of 30km. The earthquake occurred along the central segment of the Sagaing Fault and was characterized by a right-lateral strike-slip rupture, generating a ~350km-long surface rupture zone with a maximum coseismic horizontal displacement of 6 meters. The event caused extensive damage to buildings and varying degrees of destruction to infrastructure, including roads and bridges.
Situated in a critical tectonic region where the Indian Plate obliquely converges with the Eurasian Plate, the Myanmar earthquake offers valuable insights into plate boundary deformation processes. Detailed analysis of this event enhances our understanding of the deformation mechanisms along the Myanmar plate boundary and provides essential constraints for seismic hazard assessment along the southeastern margin of the Eurasian Plate. This research holds scientific significance for elucidating continental lithospheric deformation in response to oblique plate convergence. The findings contribute to regional early warning strategies and disaster mitigation efforts and offer a valuable reference for seismic risk studies in comparable tectonic settings worldwide.
This study integrates Global Navigation Satellite System(GNSS)data from across the Sagaing Fault region, establishing a comprehensive GNSS velocity field for Myanmar and addressing previous gaps in coverage along the fault’s southern segment. Using multiscale spherical wavelet analysis and GNSS velocity profiles, we examine the deformation characteristics of the region. We calculate the slip rate deficit distribution along the Sagaing Fault and assess postseismic Coulomb stress changes. Combined with historical seismicity data, we investigate the seismogenic structure and stress perturbations in surrounding areas. The key findings are as follows:
(1)The Myanmar M_S7.9 earthquake was a right-lateral strike-slip event along the central Sagaing fault. The region is affected by the northeastward oblique convergence of the Indian Plate and southeastward extrusion of crustal material from the Tibetan plateau, resulting in strong north-south shear and east-west shortening. The Sagaing fault accommodates most of this deformation, with a rapid right-lateral slip rate of approximately 21~22mm/a.
(2)High-resolution GNSS velocity profiles indicate significant fault locking at depths of 15~25km along the Sagaing Fault. The slip rate deficit analysis reveals a high locking ratio across the fault, indicating elevated seismic potential. Notably, the central segment shows lower seismic moment accumulation compared to the northern and southern segments, forming a ~300km-long seismic gap since 1900, capable of generating earthquakes exceeding magnitude 7.5.
(3)Coulomb stress modeling suggests that the earthquake significantly altered the regional stress field. Stress accumulation zones were identified at both ends of the Sagaing fault and in the central Shan Plateau to the east. These regions of increased stress transfer and loading exhibit heightened potential for future large earthquakes, underscoring the need for enhanced seismic monitoring.

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SURFACE DEFORMATION CHARACTERISTICS AND CAUSES OF THE DENGMECUO SEGMENT IN THE XIZANG DINGRI M_S6.8 EARTHQUAKE

LIANG Ming-jian, DONG Yun-xi, ZUO Hong, DAI You-lin, XIAO Ben-fu, LIAO Cheng, TAN Ling, WANG Yu-wei, LI Xiang, TANG Cai-cheng, ZHANG Wei, ZHANG Hui-ping, MENG Ling-yuan, SU Jin-rong, WU Wei-wei, LI Chuan-you, YAN Mei

SEISMOLOGY AND GEOLOGY 2025, 47 (1): 80-89. DOI: 10.3969/j.issn.0253-4967.2025.01.006

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On January 7, 2025, an M_S6.8 earthquake struck Dingri, Xizang, China. According to the focal mechanism solution provided by the USGS, this event was characterized as a normal faulting earthquake. The earthquake occurred in the southern segment of the Shenzha-Dingjie Rift system, which is located on the Qinghai-Tibet Plateau. This rift system is one of the seven major rift systems in the southern part of the Tibetan plateau and is a significant controlling structure for shallow-source seismic activity within the region. Moderate to major earthquakes in the study area are primarily distributed along these rift systems. Notably, the Yadong-Gulu Rift system experienced an M8.0 earthquake in 1411 near the southern part of Dangxiong.

The seismogenic fault of the earthquake is the Dengmecuo fault, which produced a 26-km-long surface rupture and deformation zone. The Dengmecuo fault is a branch of the southern segment of the Shenzha-Dingjie fault zone and is a Holocene active fault that controls the eastern boundary of the Dengmecuo Basin. The characteristics of the surface deformation zone in this earthquake differ between its northern and southern segments. The northern segment's surface rupture is primarily characterized by normal faulting, with a vertical co-seismic displacement of 2-3 meters. In contrast, the southern segment(the Dengmecuo segment)is mainly distributed on the eastern side of Dengmecuo Lake, with a width exceeding a hundred meters. The deformation characteristics of this segment are complex, exhibiting both extensional and compressional deformations. The extensional deformation zones in the southern segment, which align with the NNE-trending fault scarp, likely represent the tectonically seismogenic surface rupture zone of this earthquake. The compressive deformation zones, however, are believed to have formed as a result of the extensional deformation during the earthquake. These zones are influenced by seismic motion, local terrain, sedimentary characteristics, and climatic conditions and are not directly related to the fault's activity during the earthquake.

The differences in the characteristics of the northern and southern segments of the surface deformation zone highlight the complexity of the geometric structure and motion properties of the Dengmecuo fault. Moreover, the main surface deformation zone in the southern section does not align with the surface traces of the Dengmecuo fault, suggesting that the fault may be gradually developing inward into the basin.

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ANALYSIS OF BUILDING DAMAGE AND CASUALTIES OF THE 2025 DINGRI M_S6.8 EARTHQUAKE IN XIZANG BASED ON FIELD INVESTIGATION

WEI Ben-yong, ZHANG Yu-man, SHI Feng, QIAO Jun-xiang, WANG Xin, ZHANG Da

SEISMOLOGY AND GEOLOGY 2025, 47 (1): 64-79. DOI: 10.3969/j.issn.0253-4967.2025.01.005

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On January 7, 2025, at 9:05 AM, a magnitude 6.8 earthquake struck Dingri County, Shigatse City, located in the southern part of the Xizang Autonomous Region(28.50°N, 87.45°E), with a focal depth of 10 kilometers. By 7:00 PM on January 9, the earthquake had resulted in 126 fatalities and 188 injuries. A total of 27, 248 buildings were damaged, including 3, 612 collapsed structures. Timely understanding and analysis of the earthquake's damage characteristics and the causes of casualties can provide valuable references for subsequent disaster loss assessments and recovery planning.

Based on field investigations, this study provides a comprehensive overview of the earthquake damage, covering four main aspects: seismic characteristics and affected areas, seismogenic fault and aftershock distribution, building damage and influencing factors, and the distribution and causes of casualties. The study also analyzes in detail the reasons for the severe casualties in this earthquake.

The epicenter of the Dingri earthquake is located within the Lhasa block of the Tibetan Plateau. The earthquake was triggered by the Dengmecuo fault, a normal fault characterized by crustal extension due to fault slip. The maximum intensity of this earthquake reached IX degree, and the major axis of the isoseismal line runs nearly north-south, with a length of 191 kilometers and a short axis of 152 kilometers. The area affected by intensity VI or higher is approximately 23986 square kilometers, covering six counties and 45 towns(or streets)in Shigatse City, Xizang Autonomous Region. The earthquake caused a surface rupture of approximately 26 kilometers, with a maximum vertical displacement of about 3 meters.

Field investigations revealed that the building structures in Dingri County mainly consist of frame, masonry, and traditional civil structures. Among these, traditional civil structures sustained the most severe damage. In extremely and severely affected areas, the majority of civil-structure buildings were either destroyed or severely damaged, with complete or partial collapses occurring. The main factors contributing to the severe damage to civil-structure buildings include the lack of seismic resistance measures, poor construction techniques, and inadequate shear resistance and bond strength of construction materials.

The majority of casualties were concentrated in Changsuo, Cuoguo, and Quluo towns, near the epicenter. Changsuo town suffered the most severe damage, with casualties accounting for 74.60% of the total fatalities. The high casualty rate can be attributed to the strong destructive power of the earthquake, the proximity of villages to the fault lines, low seismic performance of buildings, high population density, and adverse environmental conditions such as low temperatures and oxygen deficiency.

Based on the analysis of the causes of casualties and field investigations, this study proposes targeted countermeasures and suggestions to mitigate earthquake disaster risks and minimize casualties in Xizang. These measures include enhancing active fault detection, improving earthquake early warning capabilities, reducing seismic damage risks to traditional residential buildings, strengthening emergency response measures, mitigating the risk of secondary earthquake disasters, and increasing public awareness of earthquake risks. These recommendations aim to enhance the region's earthquake prevention and mitigation capabilities and provide guidance for post-disaster recovery and reconstruction.

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THREE-DIMENSIONAL MODEL OF SEISMOGENIC FAULT AND SEISMIC ENVIRONMENT OF XIZANG DINGRI M_S6.8 EARTHQUAKE OF JANUARY 7, 2025

GUO Zhao-wu, LU Ren-qi, ZHANG Jin-yu, FANG Li-hua, LIU Guan-shen, WU Xi-yan, SUN Xiao, QI Shi-miao

SEISMOLOGY AND GEOLOGY 2025, 47 (3): 671-688. DOI: 10.3969/j.issn.0253-4967.2025.03.20250030

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At 09:05a.m. on January 7, 2025, a magnitude M_S6.8 earthquake struck Dingri County, Xizang, China, resulting in 126 fatalities and a maximum seismic intensity of Ⅸ. Occurring within a seismically active and tectonically complex region, this event drew significant attention from both the scientific community and the public. The epicenter was located near the Dengmecuo Fault, which has been preliminarily identified as the seismogenic fault.

This study utilized publicly available geological survey data, aftershock relocations, and focal mechanism solutions to construct a detailed three-dimensional geometric model of the Dengmecuo Fault. The model was developed using the SKUA-GOCAD 3D modeling platform, enabling a comprehensive analysis of the fault’s geometry. Results reveal pronounced geometric segmentation along the fault plane, with the spatial distribution of these structural features closely correlating with observed seismicity, highlighting the influence of fault geometry on earthquake generation.

The M_S6.8 Dingri earthquake occurred near a prominent structural irregularity on the Dengmecuo Fault, at point P3, where the fault plane bends into an eastward-projecting arc. This three-dimensional structural mutation likely played a role in the nucleation of the event, underscoring the relationship between fault complexity and seismic rupture. The Dengmecuo Fault, situated in the southern Tibetan plateau, is a listric normal fault characterized by a steep upper section and a gentler lower section that terminates within a detachment layer in the upper crust. It does not extend into the deeper lithosphere, indicating that it is part of the region’s shallow normal fault system. The earthquake is interpreted as the release of accumulated stress along this shallow fault structure.

To evaluate post-earthquake stress transfer and seismic hazard, Coulomb stress modeling(Coulomb 3.4)was conducted. The analysis indicates that several regional faults are now in a state of increased Coulomb stress, including the southern segment of the Dengmecuo Fault, the middle segment of the south Xizang detachment system, the southern segment of the Shenzha-Dingjie Fault, the central Yarlung-Zangbo Fault, and the midsection of the Dajiling-Angren-Renbu Fault. These fault segments are identified as potential sites for future seismic activity and merit heightened monitoring.

This study presents a detailed characterization of the three-dimensional geometry of the seismogenic fault responsible for the Dingri M_S6.8 earthquake and offers a preliminary analysis of regional seismogenic structures. The findings provide valuable insights into the tectonic setting of southern Xizang and contribute to the assessment of regional seismic hazard.

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SOURCE RUPTURE MECHANISM AND STRESS CHANGES TO THE ADJACENT AREA OF JANUARY 7, 2025, M_S6.8 DINGRI EARTHQUAKE, XIZANG, CHINA

YANG Jian-wen, JIN Ming-pei, YE Beng, LI Zhen-ling, LI Qing

SEISMOLOGY AND GEOLOGY 2025, 47 (1): 36-48. DOI: 10.3969/j.issn.0253-4967.2025.01.003

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According to the official determination of China Seismic Network, at 09:05 on January 7, 2025, an M_S6.8 earthquake(hereinafter referred to as Dingri earthquake)occurred in Dingri County(28.50°N, 87.45°E), Shigatse City, Xizang, with a focal depth of 10km. The earthquake occurred in the southern part of the Qinghai-Xizang Plateau, which is located in the intersection area of the Shenzha-Dingjie rift and the south of Xizang detachment system. The Dengmecuo fault(about 11km)is the closest to the earthquake, and the focal mechanism is tensile rupture. The earthquake had high magnitude, high intensity and shallow source, and the towns and villages in the epicenter area were relatively concentrated. In addition, the landform type of the epicenter and the surrounding area is a river alluvial plain, and the soil is soft, which amplifies the earthquake damage effect. Due to the comprehensive superposition of various factors, the earthquake caused severecasualties and building damage.

The Dingri earthquake is a shallow-source normal-fault earthquake. The ground vibration and building(structure)damage caused by the release process of seismic radiation energy are higher than other earthquakes of the same magnitude, and the surface rupture characteristics are more significant. Therefore, the in-depth study of the Dingri earthquake, the acquisition of the co-seismic deformation field and the source sliding model, and the understanding of the earthquake's seismogenic mechanism and dynamic process can provide scientific and technological support for seismic damage assessment and secondary disaster analysis. In addition, based on the fault slip model, the Coulomb stress change in the surrounding area caused by co-seismic dislocation can be calculated, which is of great significance for the scientific evaluation of the future seismic risk and potential seismic disaster risk in the adjacent area.

The Dingri earthquake occurred at a high altitude area, with an average elevation of about 4471m within 10km near the epicenter. The harsh natural conditions and the surrounding GNSS and strong seismic stations are scarce. Therefore, SAR images have become an important data source for obtaining the coseismic deformation of the earthquake and inversion of fault slip distribution. In this paper, based on the ascending and descending SAR image data before and after the Dingri earthquake taken by the Sentinel-1A satellite of the European Space Agency, the co-seismic deformation field of the Dingri earthquake was obtained by D-InSAR technology. On this basis, the source sliding model of the earthquake was jointly inverted based on the coseismic deformation data of the ascending and descending orbits, and the Coulomb stress variation characteristics of the surrounding area caused by the co-seismic dislocation were calculated. The deformation characteristics of the Dingri earthquake, the source rupture mechanism and the stress adjustment effect on the adjacent area are analyzed and discussed. Form the following understanding:

(1)The results of the coseismic deformation field of the Dingri earthquake obtained based on the D-InSAR technology ' two-track method ' show that the long axis of the coseismic deformation field of the ascending and descending orbits is nearly NS-trending. The coseismic deformation is characterized by two obvious deformation areas in the east and west and a butterfly-like stripe pattern. The LOS deformation of the ascending and descending orbits is between -0.58~0.33m and -0.80~0.66m, respectively.

(2)Based on the coseismic deformation data of ascending and descending orbits, the moment magnitude of the Dingri earthquake obtained by joint inversion is M_W7.06 by using the SDM layered model method. The rupture process of the earthquake shows a unilateral rupture characteristic from the initial rupture point to the north along the fault. The fault dislocation is a standard fault mechanism with a little strike-slip component. The length of the main rupture zone of the seismogenic fault is about 55km, and the slip distribution is concentrated in the depth range of 0~15km underground. The maximum slip is 4.25m, which occurs at a depth of 8.6km underground. The main rupture zone of the earthquake has reached the surface, located about 35~53km north of the epicenter along the strike, and the potential surface rupture length is about 18km.

(3)The results of the change in coseismic Coulomb stress show that the Dingri earthquake led to a decrease in coseismic Coulomb stress on both sides of the seismogenic fault. The Coulomb stress at the north and south ends of the fault rupture section and its surrounding areas increases significantly, and the loading amount is much larger than the earthquake-triggering threshold of 0.01MPa. There is a possibility of further felt aftershocks in these areas in the future.

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LATE QUATERNARY THROW RATE OF THE SEISMOGENIC FAULT(DENGMECUO FAULT)OF THE 2025 M_S6.8 DINGRI EARTHQUAKE IN SHIGATSE

GAO Yang, WU Zhong-hai, HAN Shuai, TIAN Ting-ting

SEISMOLOGY AND GEOLOGY 2025, 47 (3): 689-706. DOI: 10.3969/j.issn.0253-4967.2025.03.20250034

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On January 7, 2025, a significant earthquake occurred in Dingri, Shigatse, China. Both the China Earthquake Networks Center and the USGS provide focal mechanism solutions indicating that the earthquake was a normal fault event. The epicenter was located in the Dengme Cograben, part of the southern segment of the Dinggye-Xainza rift, with the seismogenic fault identified as the bounding normal fault of the Dengme Cograben, the Dengmecuo fault. The late Quaternary throw rate of this fault is crucial not only for regional seismic hazard assessments but also for understanding the east-west extensional deformation within the Tibetan plateau. Previous studies on the kinematics of the Dengmecuo fault report varying throw rates: (0.28±0.04)mm/a since ~56ka, (0.28±0.04)mm/a since ~50ka, and(0.09±0.03)mm/a since ~95ka. However, the observed maximum coseismic vertical displacement of ~3m during the January 2025 earthquake suggests that the maximum cumulative time for this displacement is approximately 37ka, based on the published late Quaternary throw rate. This is inconsistent with the ~5ka elapsed time since the most recent earthquake on this fault, highlighting the uncertainty in the late Quaternary throw rate and limiting our understanding of strain partitioning and seismic risk in the southern Dinggye-Xainza rift.

To resolve this uncertainty, we combine high-resolution remote sensing image interpretation with field geological and geomorphological surveys to determine the geometric distribution of the Dengmecuo fault. Two study sites were selected along the fault, each featuring clear faulted geomorphology suitable for dating. Low-altitude photogrammetry using an unmanned aerial vehicle(UAV)was combined with optically stimulated luminescence(OSL)and AMS ¹⁴C dating to refine the late Quaternary throw rate of the Dengmecuo fault and assess its seismic hazard.

Our results show that the Dengmecuo fault, which strikes NNW and dips NW or W, is approximately 58km long and can be divided into northern, central, and southern segments. The northern segment is defined by the Laangshuiku area, while the southern boundary is located at the edge of Pum Qu. In the northern study site, vertical offsets of 19.2(+3.5/-2.3)m on the T2 alluvial fan and 8.0(+0.9/-0.7)m on the T1 alluvial fan correspond to formation ages of(28.3±1.4)ka and(12.0±1.5)ka, respectively. By matching the vertical offsets with their respective formation ages, we estimate a throw rate of (0.7±0.1)mm/a. However, the throw rate for the T1 fan is uncertain, as its vertical offset is smaller than the cumulative displacement since its formation. At the southern study site, combining a vertical offset of 5.3(+0.3/-0.5)m with the formation age of the T1 terrace ((9.2±1.0)ka), we calculate a throw rate of(0.6±0.1)mm/a.

Overall, our results indicate late Quaternary throw rates of(0.7±0.1)mm/a since ~28ka and(0.6±0.1)mm/a since the Holocene. Additionally, using the relationship S=D/R_x, where S is the slip rate, D is displacement, and R_x is the recurrence interval, we estimate a slip rate of(0.5±0.1)mm/a based on the average value of the maximum displacement(2.5~3m)of 2025 Dingri M_S6.8(Shigatse)earthquake as 2.75m and the interval of paleoseismic events during the Holocene as(5500±1100)a. This result is consistent with the throw rate of(0.6±0.1)mm/a since the Holocene determined from faulted geomorphic surfaces.

Finally, combining the throw rate of (0.6±0.1)mm/a since the Holocene with the ~5ka elapsed time since the most recent earthquake, we conclude that the Dengmecuo fault had accumulated 2.5~3.5m of coseismic displacement before the 2025 Dingri M_S6.8 earthquake, corresponding to a magnitude of M_W6.9-7.0. These parameters align with the 2025 M_S6.8 earthquake, indicating that the Dengmecuo fault posed a significant seismic risk prior to the event.

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CRUSTAL DEFORMATION CHARACTERISTICS AND PROBABILITY PREDICTION OF STRONG EARTHQUAKE RISK IN XINJIANG AND ITS ADJACENT REGION

CHEN Chang-yun, YIN Hai-quan

SEISMOLOGY AND GEOLOGY 2025, 47 (2): 384-404. DOI: 10.3969/j.issn.0253-4967.2025.02.20240151

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Based on the GNSS velocity field, we analyzed the present-day crustal deformation characteristics of Xinjiang and its adjacent regions before the January 23, 2024, Wushi earthquake using the spherical least squares configuration method. Based on the fundamental concept of active blocks, Xinjiang and its neighboring areas were divided into 17 active blocks by integrating regional seismic geological data. The slip rates of the boundary fault zones of these active blocks were then calculated using a three-dimensional elastic block model. Based on this block delineation, the study area was further divided into 91 potential seismic hazard zones. We incorporated geodetic observations, including fault strike-slip rates and dilatational strain rates derived from the GNSS velocity field, into the conventional probabilistic forecasting of significant seismic hazards. The relationship between the Wushi 7.1 earthquake and the regional crustal deformation characteristics, as well as the prediction results of the probability of strong earthquakes, was comprehensively analyzed.
The direction and magnitude of GNSS velocity field motions in the study area under different dynamical backgrounds are distinctly characterized by zoning. GNSS stations east of longitude 76° move toward the north or northeast, while those on the west side move north or northwest. The velocity field difference is primarily evident on the north and south sides of the Tianshan Mountain. The velocity change of GNSS sites from the Tibetan plateau to the Tarim Basin is minor, but it significantly decreases after crossing the Tianshan Mountain, indicating that the Tianshan Mountain tectonics absorb most of the remote effects of the Indo-Eurasian plate collision. The principal strains obtained from the least-squares configuration results reveal that the extrusion characteristics are most prominent near the western section of the Southern Tianshan Mountains and the Altyn Tagh fault zone. In the western section of the Southern Tianshan Mountains, the direction of the principal compressive strains is perpendicular to the tectonic direction in the region. This suggests that the region is primarily influenced by a force perpendicular to the tectonic direction, resulting in the predominant retrograde movement of major fault zones in the area. Moreover, in addition to the western section of the Southern Tianshan Mountains, the region with a greater main compressive strain is the Altyn Tagh fault zone. The direction of the main compressive strain intersects obliquely with the Altyn Tagh fault zone, suggesting that the force background is linked to the left-lateral reverse slip movement of the Altyn Tagh fault zone.
The results derived from the inversion of the three-dimensional elastic dislocation model reveal that the motion features of the main active faults within the study area indicate a predominance of dextral slip along the northwest-trending fault zones in the Tianshan region, while sinistral slip motion is primarily observed along the northeast-trending or northeastern fault zones. Apart from the Altyn Tagh fault zone, the strike slip rate of the dextral-slip fault zones is notably higher than that of the sinistral-slip fault zones. The fault zones at the northern edge of the Junggar Basin and the major faults in the Tianshan region are primarily characterized by extrusion movements. The extrusion rate of the fracture zones in the South Tianshan Mountain is higher than that in the North Tianshan Mountain. Specifically, the west section of the Keping fault zone and the west section of the Nalati fault zone exhibit the most prominent extrusion movements.
The study area has been divided into 91 potential seismic hazard zones based on block delineation and the findings from previous research. The slip rates and regional surface strains of the major faults obtained from the inversion are utilized in classical probabilistic predictions to derive quantitative results regarding the strong earthquake hazard in the study area over the next 50 years. The results indicate that the strong earthquake hazard is primarily concentrated in the western section of the Southern Tianshan region. This includes areas such as the north-east or nearly east-west-trending Maidan fault, the Nalati fault, and the Usun Ridge Fault, as well as the north-west-trending Talas-Fergana fault zone and the north-west section of the Kyzyltau fault zone. Furthermore, the probability of strong earthquakes is elevated in the northern Luntai fault compared to the surrounding faults. In the northern Tianshan region, areas with relatively high probabilities of strong earthquakes include the Fukang fault and the western section of the Bogda fault.
The seismic mechanism solution reveals that the M7.1 Wushi earthquake was a thrust earthquake, aligning with the characteristics of the Maidan fault zone. In this zone, the seismogenic fault is primarily influenced by extrusion motion. The Wushi earthquake occurred in the Maidan fault zone, situated at the border of the high shear strain rate zone and the high probability hazard zone. This occurrence validates the effectiveness and accuracy of the probabilistic prediction method.

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GROWING HISTORY AND GEOMORPHIC RESPONSE OF THE EASTERN TERMINATION OF KASHI ANTICLINE, SOUTHWESTERN TIAN SHAN: AN INTEGRATED ANALYSIS OF GEOLOGY, GEOMORPHOLOGY, SEISMIC REFLECTION PROFILE AND MAGNETOSTRATIGRAPHY

HE Peng-yu, LI Tao, CHEN Zhu-xin, CHEN Jie

SEISMOLOGY AND GEOLOGY 2025, 47 (2): 369-383. DOI: 10.3969/j.issn.0253-4967.2025.02.20240157

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The Kashi anticline, located along the leading edge of the Kashi foreland thrust system in the southwestern Tian Shan of China, confronts the Atushi Anticline to the north and connects with the Mingyaole Anticline to the west. The Kashi anticline manifests at the surface as an elongated hillock with a nearly EW strike. The morphology of the anticline is roughly box-shaped, with the southern limb being gentler compared to the northern limb. As a significant component of the Tianshan orogenic belt’s frontal zone, the study of the tectonic evolution of the Kashi Anticline is crucial for understanding the Cenozoic tectonic deformation and crustal shortening processes of the Tian Shan. Previous studies on this fold are primarily focused on its surface-expression part, with little or no focus on its lateral termination that is not expressed on the land surface, which has limited the comprehensive understanding of the anticline’s overall evolutionary process. The study employs the depth-relief area method, combined with high-resolution seismic reflection profile data, to conduct a detailed structural analysis of the eastern termination of the Kashi anticline.
Through meticulous interpretation and quantitative analysis of the seismic profiles, the following key insights have been obtained: Firstly, along the seismic profile, the Cenozoic strata are approximately 6.8km thick, while the Mesozoic-Paleozoic strata are about 2.2km thick. The eastern termination of the anticline detaches along the Paleogene unit, with a depth of ~6.8km. This detachment layer governs the deformation patterns and magnitudes of the overlying strata. Secondly, along the seismic profile, the total shortening of the anticline is estimated to be(882±79)m, of which approximately 94% is attributed to shear shortening, and about 6% is due to curvietric shortening. During the folding process, materials with an excess area of ~3.4km² enter the cross section. Thirdly, according to the analysis of growth strata and published magnetostratigraphic data, the folding of the eastern termination initiates at the age of ~2.1Ma, which implies that the initiation age of the fold should be much older than 2.1Ma. The shortening rate remains at an approximate constant of ~0.4mm/a since the folding initiation. Fourthly, for the pre-growth strata, the uplift of the anticline gradually increases upward with depth, reaching a maximum of approximately 770m at the top boundary of the pre-growth strata. Analysis of the growth strata indicates that the uplift rate either keeps a constant of ~0.4mm/a, or increases significantly from an earlier rate of ~0.1mm/a to a later rate of 0.4 mm/a at the age point of ~1.6Ma. Notably, because the uplift rate is smaller than the sediment rate, the fold exhibits no expression on the surface of the anticline.
Our study exemplifies that an analysis of the buried lateral termination of a fold can well determine the detachment level, shortening and uplift histories, initiation age of the fold, as well as whether or not the excess area enters the cross section during the folding process. These constraints provide a completer and more reliable basis for understanding the entire growing history of the fold. Furthermore, the results demonstrate that the analysis of buried structures in the frontal zones of orogenic belts is indispensable for a comprehensive understanding of regional tectonic deformation characteristics and evolutionary history.

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THE RANGE OF DEFORMED ZONE BASED BY ACTIVE FAULT OFFSET BASED ON STATISTICAL ANALYSIS OF SURFACE RUPTURE ZONE WIDTH

ZHANG Wei-heng, ZHANG Dong-sheng, CHEN Jie, TIAN Qin-jian, HE Wan-tong

SEISMOLOGY AND GEOLOGY 2025, 47 (1): 345-366. DOI: 10.3969/j.issn.0253-4967.2025.01.020

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Analyzing the statistical data on the widths of earthquake surface rupture zones is one of the most objective methods for determining the extent of active fault offsets and deformed zones. This information is crucial for establishing the setback distances for significant engineering projects in areas affected by active faults. In this study, we collected data from 92 cases to compute the widths of surface rupture zones and subsequently analyzed the extent of active fault offsets and deformed zones. Specifically, our dataset includes 75 cases with surface rupture zone widths extracted from published sources and 49 cases with available surface rupture vector data.

When compiling the statistical data on surface rupture widths, we categorized the data based on whether the ruptures occurred along straight fault segments or along more geometrically complex segments. For the vector data, we normalized the distributed rupture length and primary rupture length for each case to determine the distribution proportion of the rupture zones relative to fault distance.

The statistical analysis of document data shows that the total width of surface rupture zones in geometrically complex sections of normal, thrust, and strike-slip faults does not exceed 8100m, 3700m, and 10100m, respectively. In contrast, the widths of surface rupture zones in straight fault sections are generally narrower, with maximum widths of 160m, 120m, and 400m for normal, thrust, and strike-slip faults, respectively. The vector data further reveal that the maximum distances between the distributed ruptures and the primary fault are as follows: 19212m for the hanging wall of normal faults, 16244m for the footwall of normal faults, 7579m for the hanging wall of thrust faults, 4216m for the footwall of thrust faults, and 120456m for strike-slip faults. Moreover, the maximum distances from the primary fault to the margin of the closely distributed rupture zones are 700m, 200m, 1000m, 400m, and 500m, respectively. It is important to note that when excluding exceptional cases, such as earthquakes associated with fold-related faults or gently dipping thrust faults, the maximum distance from the margin of the closely distributed rupture zone to the primary fault is as follows: 400m for the hanging wall of normal faults, 200m for the footwall of normal faults, 500m for the hanging wall of thrust faults, 200m for the footwall of thrust faults, and 400m for strike-slip faults. Based on this comprehensive analysis, we suggest that the range of active fault offset and deformed zones should be considered as 400~500m from the primary fault. However, further research is needed to accurately determine the extent of fault offsets and deformed zones in areas with complex structural features, such as fault bends, step zones, fault tails, and the hanging walls of foreland thrust faults.

Future studies would benefit from incorporating more extensive and detailed surface rupture data. Continued data collection is essential to improve the accuracy and robustness of the results.

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INSAR COSEISMIC DEFORMATION AND SEISMOGENIC STRUCTURE OF THE 2024 M_W7.0 WUSHI EARTHQUAKE

CHEN Zi-long, LIU Gang, LI Qi, CHEN Wei, ZHAO Xin-yu, LIN Mu, TAO Long-wen, QIAO Xue-jun, NIE Zhao-sheng

SEISMOLOGY AND GEOLOGY 2025, 47 (2): 429-447. DOI: 10.3969/j.issn.0253-4967.2025.02.20240142

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On January 30, 2024, an M_W7.0 earthquake struck the Wushi region of the southern Tianshan Mountains, Xinjiang, China. This earthquake, located in a tectonically active zone dominated by intense crustal shortening and thrust faulting, providing a valuable opportunity to investigate fault geometry and rupture mechanisms in the region. We utilized Sentinel-1 InSAR data combined with advanced inversion techniques to analyze the coseismic deformation field, determine fault parameters, and explore the spatial relationship between the mainshock and aftershocks.
High-resolution coseismic deformation fields were generated using D-InSAR processing of Sentinel-1A ascending and descending orbit data. Nonlinear inversion methods were employed to calculate fault geometry and sliding distribution, with both single-fault and dual-fault models tested to accommodate the complex faulting characteristics. Residual analysis was performed to examine the relationship between the mainshock and the M_W5.7 aftershock, and geological surveys were used to validate fault models and rupture characteristics.
The maximum line-of-sight(LOS)displacement of the coseismic deformation field reached 70cm, displaying an elliptical pattern along the Maidan Fault. The dual-fault model revealed significant geometric complexity: the fault strike rotates clockwise by 20°~25° east of the epicenter, and the dip angle decreases from 60° in the west to 40° in the east. Fault slip was primarily concentrated west of the epicenter, characterized by high-angle thrusting with a left-lateral component, while slip in the eastern segment was lower in magnitude and relatively dispersed. The overall distribution exhibited shallow slip deficit. The correlation between geometric variations and sliding distribution suggests the presence of a geometric barrier east of the epicenter, acting as an obstacle to rupture propagation. The coseismic rupture was confined between the Yushanguxi River and the Wushi depression, with fault steps and structural complexities on the eastern and western boundaries limiting the rupture extent. The M_W5.7 aftershock produced a clear LOS deformation field, with the fault strike deviating by ~10° from the mainshock trace and dipping southeast. The surface trace of the aftershock fault closely aligned with mapped surface ruptures, and the shallow slip magnitude matched the observed vertical offsets from geological surveys.
We also demonstrates that fault geometry plays a significant role in controlling rupture propagation and termination. The geometric barrier east of the epicenter effectively limited eastward rupture propagation, while a wide fault step near the Yushanguxi River constrained the western rupture. The Wushi earthquake was identified as a blind rupture event, with no significant primary surface rupture. The distribution of secondary geological hazards aligned well with fault slip characteristics, and the spatial relationship between aftershock slip and the mainshock highlights fault segmentation within the Ush thrust belt.

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SEISMOLOGY AND GEOLOGY 2025, 47 (3): 0-0.

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CRUSTAL DEFORMATION CHARACTERISTICS AND RELEVANT SEISMIC HAZARD OF THE TAIYUAN BASIN

CHEN Qian, ZHANG Zhu-qi

SEISMOLOGY AND GEOLOGY 2025, 47 (1): 189-213. DOI: 10.3969/j.issn.0253-4967.2025.01.012

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The Taiyuan Basin(TB) is located at the middle part of the Shanxi Graben belt(SGB), which is the tectonic boundary between the Ordos active block in the West and the North China Plain in the East. The SGB comprises several echelon left-stepping depression basins lining up in NNE direction. Previous studies of active tectonics and crustal kinematics indicate that the present deformation of the SGB is controlled by the NNE dextral shear and NW extension between the blocks on both sides of it, but how the shear and extension are accommodated by basins remains in question. To answer the question, researchers in active tectonics have made more effort to investigate the slip type and rate of faults bounding basins. By contrast, inadequate attentions were paid to the kinematic characteristics of the internal deformation within basins. Recent studies on focal mechanisms find that not only normal slip earthquakes but also strike-slip earthquakes, which account for a major proportion of the whole seismicity, occur in the depression basins of the SGB.As can be seen, faulting with dominating normal slip on basin boundary faults cannot easily and reasonably explain how the SGB deforms at present. To comprehensively understand the present deformation mechanism of the SGB, further exploration is needed, which should be based on both the deformation characteristics of basin boundary faults and the kinematic characteristics of the relevant blocks including basins. Compared with other basins in the SGB, the TB has relatively simple features in tectonics, which an explicit kinematic model may describe. Therefore, the TB is potentially proper to demonstrate how basins deform in the SGB.

Developing typical tectonics like other basins of the SGB, the TB behaves oddly at the same time in terms of seismicity. Constituting the middle segment of a large-scale active block boundary and developing active faults reaching the middle and lower crust, this tectonic basis jointly imply the TB is eligible for the occurrence of large earthquakes. However, the historical record of earthquakes with a magnitude greater than 7 is lacking in the TB.In contrast to that, several earthquakes with a magnitude of 7 or even up to 8 have occurred in the last thousand years in the Xinding Basin and the Linfen Basin adjacent to the TB.So far, it is still uncertain how possible and how urgent a big earthquake could strike the TB in the future. To address this question, a thorough evaluation of the accumulation state of seismic energy on the boundary faults of TB is necessary.

Modeling the kinematics of block and fault with constraints from GPS velocity usually gives the spatial distributions of slip rate and locking ratio on faults, and also Euler rotation velocities and strain rates of blocks. However, due to the azimuthal heterogeneity and the sparsity in the distribution of GPS stations, the result of modeling block-fault kinematics sometimes concerns trade-offs between variables, and the optimal solution may be discrepant with the given tectonic knowledge. Furthermore, for the fault with a low dip angle, the overlap of surface strain due to faulting and that due to internal deformation of the hanging wall block could be large, which may aggravate the mentioned trade-off and discrepancy. As the block-fault kinematic model related to TB involves the above issues, appropriate conditions may be carefully selected to enhance the constraints of modeling.

In this study, a three-dimensional geometric model of two boundary faults of the TB is constructed based on the data from earthquake geology and deep exploration. A kinematic model of the blocks and the boundary faults relating to the TB is constructed based on the geometric model. According to previous studies on regional tectonics, this study attempted to obtain appropriate a priori information to provide better constraints on the modeling. Several strategies of modeling were designed based on the characteristics of a priori information. Constrained by a priori conditions, the GPS velocities at 137 sites from two data sources are simulated to get the fundamental kinematic features for the blocks and the boundary faults concerning the TB, which include the vertical axis rotation velocity and translational velocity at the centroid of the TB and the blocks in its neighbor, the distribution of locking ratio on the fault planes, and additionally the crustal strain rate within the basin. An apparent optimal model is obtained considering not only its fitting to the GPS velocities but also the good correlation between the observational features of principal axes of strain rate and that from the modeling. The results of the apparent optimal model show that the TB is spinning clockwise, and bearing the internal strain with principal axis orientating in NW.The blocks on the west side and the east side of the TB are both translating toward approximately SE under the stable Eurasian reference frame, but the east block TH is moving faster with more southward component relative to the west block LL.Furthermore, the LL and TH blocks are spinning counterclockwise. As the western boundary of the TB, the Jiaocheng fault is a normal fault with a right-lateral component. In contrast, the Taigu fault, which is on the eastern side of the basin, is a right-lateral fault with a normal component. According to the above features of the apparent optimal model, it is inferred that the combination of the tensional function across the western basin boundary and the strike-slip shearing along the eastern boundary contributes to the clockwise rotation of the TB and also causes the internal NNE dextral shear and NW extension within the basin. The model results also show extensive locking areas on the Jiaocheng fault and the Taigu fault. Taking into account of the relevent research on the recurrence of paleo-earthquakes since the late Pleistocene, the locking status of the fault indicates that the Jiaocheng fault is close to the occurrence of an earthquake greater than M7.5.In contrast, the Taigu fault has accumulated enough energy for an earthquake around M6.7, which appeals to attention and further studies on the possible occurrence of strong earthquakes in the vicinity of the TB.

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HIGH-RESOLUTION SHALLOW CRUSTAL S-WAVE VELOCITY STRUCTURE IMAGING IN THE KASHGAR, XINJIANG

HUA Qian, PEI Shun-ping, LI Tao, LIU Han-lin, LIU Wei, LI Lei, LI Jia-wei, YANG Yi-hai

SEISMOLOGY AND GEOLOGY 2025, 47 (2): 533-546. DOI: 10.3969/j.issn.0253-4967.2025.02.20240160

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High-density short-period seismometers are increasingly employed in urban environments and local geological structures to explore the crustal structure, their high-resolution images facilitate the precise identification of subsurface faults, the spatial distribution of mineral resources, and conduct building response analysis. In this study, 101 short-period seismometers were deployed across Kashgar for continuous seismic monitoring. Integrating with ambient noise tomography, high-resolution seismic velocity imaging of the shallow crust within the Kashgar was conducted. This study aims to delineate potential subsurface faults, elucidate their tectonic genesis, and provide critical insights for regional seismic risk assessment.
The empirical Green’s functions extracted from the cross-correlation of the Z component yielded a total of 1 752 Rayleigh wave phase velocity and group velocity dispersion curves. By applying one-step ambient noise tomography, the three-dimensional S-wave velocity structure of the study area was resolved down to a depth of 5km, achieving a lateral resolution of approximately 0.04°. The horizontal and vertical cross-sections of the S-wave velocity model reveal that the S-wave velocities within the upper 5km of the crust in the study area are generally lower than the global average velocity model. The Kashgar Depression is characterized predominantly by Cenozoic sediments, with continuous Quaternary alluvial deposits reaching thicknesses of up to 10~12km. The relatively weak Cenozoic sedimentary basin likely contributes to the overall low S-wave velocities observed in the region.
The velocity structures exhibit remarkably consistent patterns in varying depths. Below the depth of 1.2km, three notable low-velocity anomalies(LVAs), labeled L1, L2, and L3, are identified beneath the Kashgar. Among these, L1 and L2 form an approximately 16km long, east-west trending bowtie-shaped LVAs that align with the structural trend of the Kashgar anticline. These anomalies cover much of central Kashgar and extend nearly vertically to depths shallower than 5km, showing variation in shape and size at different depths. L3, located at the central southern edge of Kashgar, appears as a semicircle with a diameter of about 10km. Its extent diminishes gradually with increasing depth, which may indicate lithological variations at different depths.
Based on the integration of seismic reflection profiles, we infer that the frontal zone of the Southwestern Tianshan fold-and-thrust belt has developed multiple north-dipping thrust structures and south-dipping secondary thrust faults propagating toward the basin. These deformations penetrate the entire sedimentary cover, forming multi-level detachments at varying depths. Notably, the slippage of the mud layer(approximately 4km deep)at the base of the sedimentary cover in the Kashgar Depression represents the shallowest detachment layer identified in previous studies. This suggests that the multi-layered weak slippage zones within the sedimentary sequence of the Kashgar Depression may be responsible for the formation of the bowtie-shaped LVAs. Mechanically weak detachment layers likely play a key role in shaping these anomalies.
Furthermore, the Kashgar-Atushi fold-and-thrust system has experienced both lateral propagation and along-strike shortening during ongoing tectonic activity, resulting in the progressive advancement of the fold-and-thrust system towards the Kashgar Depression, which lies adjacent to the collapse-reverse fault system, may also have been subjected to intense tectonic action to form similar faults. Consequently, the east-west trending bowtie-shaped LVAs may indicate the presence of a secondary blind fault parallel to the Kashgar anticline. This inferred fault crosses the tectonic boundary between the southwestern Tianshan and Pamir regions, exhibiting a significant east-west structural discontinuity. Geological and geomorphological evidence reveals that the Kizilsu River, the largest river in the region, and its tributaries intersect the LVAs beneath Kashgar. We hypothesize that these LVAs may also reflect high-porosity fluvial sediments and folded scarps associated with paleo-river deformation.
In summary, high-density short-period seismic array imaging enables the precise detection of shallow subsurface structures in urban environments. This approach provides robust datasets for urban active fault detection, seismic amplification effect evaluation, and subsurface resources and energy exploration and development.

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THE DISTRIBUTION AND RESEARCH PROGRESS OF MAIN MUD VOLCANOES IN CHINA

WANG Qian, PENG Lai, JIANG Yu-han, ZHOU Qi-chao, GAO Xiao-qi

SEISMOLOGY AND GEOLOGY 2025, 47 (1): 90-116. DOI: 10.3969/j.issn.0253-4967.2025.01.007

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This paper provides an overview of the distribution and research progress of mud volcanoes in China, and offers a comparative analysis of the physical and geochemical characteristics of mud volcano emissions from various regions. The findings are as follows:

Mud volcanoes in China are predominantly located along faults or fault zones, primarily in seismically active regions such as Xinjiang, Tibet, and Taiwan. A comparative analysis of emissions from different regions reveals that the solid components—primarily minerals like quartz and montmorillonite—are similar across locations. The liquid emissions generally exhibit high salinity. Geochemical analysis indicates regional differences in the sources of the emitted mud water: in Xinjiang, it mainly derives from a mixture of ancient sediment pore water and atmospheric precipitation; in Tibet, it originates from deep groundwater and atmospheric precipitation; and in Taiwan, it comes from marine sediment pore water mixed with atmospheric precipitation.

In terms of gas emissions, methane is the predominant gas released by most mud volcanoes in the study area, with smaller amounts of ethane, carbon dioxide, and other hydrocarbons. Notably, some mud volcanoes in Taiwan region emit higher concentrations of carbon dioxide and nitrogen, with smaller amounts of methane. Carbon isotope analysis of the emitted gases shows that the methane is of organic origin, as indicated by δ13C1 values.

In addition to the geochemical analysis, the microbial communities associated with mud volcanoes are also significant. The origin of methane suggests the presence of methane-producing microbial communities in the surrounding environments of onshore mud volcanoes. These microbes, including aerobic methane-oxidizing bacteria and anaerobic methane-oxidizing archaea, play a role in the formation of the emitted gases. In particular, these microorganisms are found in the soil environments of mud volcanoes in eastern Taiwan region, Wusu(Xinjiang), and Dushanzi(Xinjiang), where they use carbon dioxide as a carbon source to produce methane. In submarine mud volcanoes, the eruption process provides conditions for the growth of marine microorganisms, including methane-producing bacteria.

Mud volcanoes are generally triggered by four main factors: volcanic activity, tectonic activity, sedimentary processes, and anthropogenic influences. Given their prevalence in seismically active zones, the activity of mud volcanoes is often induced by seismic events. Eruptions typically result from increased pore pressure within the surrounding rock layers. Significant physical and chemical anomalies, including elevated gas emissions and changes in the height of the mud surface, are observed before and after seismic events. For example, following the establishment of a real-time monitoring system for the Wusu mud volcano in Xinjiang in 2011, multiple earthquakes in the area were associated with changes in the mud volcano's liquid level and increased emissions of methane(CH₄)and carbon dioxide(CO₂), which gradually returned to background levels post-earthquake. These geochemical changes have been observed in other regions as well, such as the hydro geochemical changes in the north Tianshan Mountains, following the Xinyuan M_S6.6 earthquake.

These observations suggest that mud volcano emissions may serve as indicators of seismic activity. Long-term monitoring of mud volcanoes could potentially offer a means of predicting seismic events.

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GEOLOGICAL HAZARD CHARACTERISTICS AND MACRO-SCOPIC EPICENTER OF WUSHI M_S7.1 EARTHQUAKE ON JANUARY 23, 2024, XINJIANG

CHEN Jian-bo, ZHENG Li-ming, LI Tao, CHEN Jie, YAO Yuan, QIAN Li, ZHANG Bo-xuan, HU Zong-kai, LIU Guan-shen, LI Jin

SEISMOLOGY AND GEOLOGY 2025, 47 (2): 561-576. DOI: 10.3969/j.issn.0253-4967.2025.02.20240066

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The Wushi M_S7.1 earthquake is the largest seismic event in Xinjiang in the past decade and the most significant earthquake in the Tianshan seismic belt since the Suusamyr M_S7.3 earthquake in Kyrgyzstan in 1992. The microseismic epicenter is located at the transition between the Keping nappe structure belt and the Kuqa nappe belt in the southwestern Tianshan Mountains, near the intersection of the southern Tianshan Mountains and the Wushi Depression. This region is a compressional fault depression valley formed in the context of Tianshan orogeny. The northern boundary of the valley is controlled by the Maidan reverse fault zone, while multiple rows of newly developed linear uplifts and piedmont fault scarps in the northern depression are governed by low-angle overthrust and recoil faults. Focal mechanism analysis indicates that both the main shock and aftershocks exhibit a compressional thrust-type mechanism, consistent with the structural characteristics of the Wushishan front depression. Post-earthquake investigations revealed relatively minor casualties and structural damage, but secondary geological disasters were severe. Using field surveys, large-scale satellite image analysis, and drone aerial photography conducted immediately after the earthquake, this study investigates the spatial distribution, types, and development characteristics of seismic-induced geological hazards in various gullies within the affected region. Although no large-scale surface ruptures were observed at or near the epicenter, extensive seismic geological hazards were identified, providing crucial insights for determining the macroseismic epicenter and assessing the post-disaster intensity and loss in the earthquake area.
Geological hazards induced by the Wushi earthquake were primarily concentrated in Biediligou, Qialematigou, Cocriu Musugou, and adjacent mountainous areas within the VII-degree seismic intensity zone. The most severe damage occurred in the Biediligou-Qialematigou region, where the macroseismic epicenter was located, with diverse types of secondary disasters, including rockfalls, landslides, rolling stones, bank slope collapses, subgrade settlement cracks, and ground fissures. Some ground fissures were accompanied by displacement. Seismic geological hazards were predominantly observed near the microseismic epicenter and within 10km of the north and south sides of the fault zone, with collapses being the most prominent, followed by pavement cracking and riverbank slope failures caused by ground fissures and uneven subgrade settlement. Post-earthquake investigations also identified numerous concentrated surface tension and shear cracks in the macroseismic epicenter, alongside earthquake-induced collapses, landslides, slope instabilities, subgrade settlements, and structural failures. Coseismic InSAR deformation field and image offset analysis revealed a maximum line-of-sight displacement of approximately 40cm and a minimum displacement of -16cm. The long axis of the deformation zone trends NE, with its strongest deformation occurring between Biediligou and Qialamatigou. This spatial distribution aligns well with the observed ground fissures and seismic deformation zones near the macroseismic epicenter, indicating that structural deformation plays a critical role in controlling the formation of earthquake-induced geological hazards.

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STUDY ON FAULT DEFORMATION CHARACTERISTICS AND SEISMIC HAZARD IN THE KEPING THRUST BELT

ZHU Shuang, GUO Nan-nan, PANG Ya-jin

SEISMOLOGY AND GEOLOGY 2025, 47 (2): 448-462. DOI: 10.3969/j.issn.0253-4967.2025.02.20240147

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As one of the most seismically active regions in China, the southwestern Tianshan exhibits the necessary tectonic conditions and energy accumulation for earthquakes exceeding magnitude 6. Investigating the region's tectonic deformation characteristics is crucial for understanding the background of strong earthquakes and assessing future seismic hazards.
In this study, we compiled and analyzed multi-period GNSS velocity fields from domestic and international sources, generating a fused velocity field. The results indicate that the crustal deformation of the Tianshan seismic belt is spatially heterogeneous, influenced by the combined effects of the clockwise rotation of the Tarim Basin and the northward thrust of the Pamir Plateau. Additionally, three north-south profiles across the study area were analyzed. The western Tianshan(Profile 1)exhibits a higher north-south compression rate, which gradually decreases eastward, consistent with the velocity field trends.
Using the fused GNSS velocity field, we calculated the strain rate field through the least-squares collocation method, obtaining strain characteristics of the Keping thrust belt and surrounding areas. The Piqiang fault zone serves as a boundary, with compressive strain on the western side of the Keping thrust belt exceeding that on the eastern side. The average surface strain rate is -3.3×10^-8/a in the west and -1.2×10^-8/a in the east. Similarly, the maximum shear strain follows this pattern, with values of 2.7×10^-8/a in the west and 1.1×10^-8/a in the east, indicating distinct deformation characteristics on either side of the Keping thrust belt.
Focal mechanism solutions of earthquakes(M≥4.0)since 1976 were collected, and stress inversion analysis was conducted at various depths. Earthquakes in the Tianshan region predominantly occur within the upper 50km of the crust. The results reveal a nearly north-south principal compressive stress orientation, perpendicular to the Tianshan orogenic belt, aligning with the regional surface principal compressive strain rate. However, due to the presence of conjugate strike-slip faults and strike-slip earthquakes in the northern and southern Tianshan hinterland, local horizontal principal stress directions deviate from the regional trend.
Integrating InSAR-derived deformation data with GNSS velocity field results, we calculated fault slip deficit rates and slip rates for major faults in the Keping thrust belt using a three-dimensional block model. The western Keping fault zone exhibits a higher compression rate of(3.1±0.3)mm/a, whereas the eastern section has a lower rate of(0.3±0.2)mm/a. The Maidan fault's western section has a compression rate of(2.7±0.5)mm/a, increasing to(3.7±0.4)mm/a in the east. Additionally, the left-lateral strike-slip rate is higher in the western Keping fault zone((1.5±0.3)mm/a)compared to the eastern section((0.5±0.2)mm/a). The Maidan fault follows a similar pattern, with strike-slip rates of(0.9±0.5)mm/a in the west and(2.1±0.4)mm/a in the east. The slip deficit rate distribution indicates high values in the western Keping fault zone, corresponding to the Jiashi earthquake swarm, while the eastern section exhibits lower deficit and slip rates, potentially due to a multilayer nappe structure. In the Maidan fault zone, the western section has a lower slip deficit and slip rate, suggesting weak crustal strength and limited stress accumulation, whereas the eastern section has higher values, correlating with the Wushi earthquake and subsequent energy release.
Finally, based on the calculated strain field and the global focal mechanism earthquake catalog(1976—2021), we applied the SHIFT_GSRM2f model developed by Bird et al. to predict shallow earthquakes. The highest predicted seismic hazard values are concentrated in the southwestern Tianshan, particularly in the Pamir region, which has a higher risk of strong earthquakes than the Keping thrust belt. However, the Keping thrust belt remains one of the most seismically hazardous areas in the Tianshan region, underscoring the continued seismic risk in southwestern Tianshan.

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STRUCTURAL SETTING AND IMPLICATIONS OF THE 2015 PISHAN M_W6.4 EARTHQUAKE IN THE FRONT OF WESTERN KUNLUN

YANG Wen-xin, LI Tao, CHEN Jie, YAO Yuan

SEISMOLOGY AND GEOLOGY 2025, 47 (2): 507-532. DOI: 10.3969/j.issn.0253-4967.2025.02.20250049

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As the dynamic hub between collisional orogenic belts and foreland basins, the formation and propagation of foreland fold-and-thrust belts are often accompanied by destructive earthquakes. In this process, the detachment, which is regarded as an incompetent layer, plays a significant controlling role in the propagation of the thrust system and the occurrence of strong earthquakes. Therefore, research focused on the structural patterns and physical property architecture of foreland fold-and-thrust belts is conducive to analyzing their activity characteristics and seismogenic patterns, thereby providing a basis for regional seismic hazard assessments.
The western Kunlun orogenic belt is situated at the Qinghai-Xizang Plateau’s northwestern margin and the Tarim Basin’s southwestern edge. Governed by the convergence of the Indian and Eurasian plates, the compressive collision between the Qinghai-Xizang plateau and the Tarim Basin has led to the formation and propagation of the Western Kunlun foreland fold-and-thrust system, triggering intense and frequent tectonic and seismic activities within the region. A M_W6.4 earthquake occurred in Pishan on July 3, 2015 in the front of western Kunlun, which was one of the most destructive seismic events that happened in Xinjiang in the recent decade. The epicentral area of this earthquake experienced an intensity of VIII, with many regions feeling strong tremors. The disaster area was vast, affecting a large population, and was accompanied by hazards such as sand liquefaction, ground fissures, and collapses. Studies on this event will provide an opportunity to better understand active structures, stress state, and future seismic hazard of the front of western Kunlun and the adjacent region.
Synthesizing geology, geomorphology and seismology studies, Slik Anticline, located on the western Kunlun foreland fold-and-thrust belt, is regarded as the seismogenic fault of this event. The Slik Anticline is located within the Guman fold belt of the Hotan thrust belt, which lies in the eastern segment of the western Kunlun foreland. The Slik ramp, situated beneath the Slik Anticline, is approximately at a depth of 10 to 15km, with a ramp angle of about 20 degrees. The Pishan earthquake ruptured blind ramp under the Slik Anticline. From north and shallow to south and deep level, the fault is revealed with the structural style of lower flat, ramp and upper flat and may merge with other thrust in a deeper part near to the hinterland. The upper and lower flats are corresponded to regional detachment of lowest Paleogene and inner Cambrian incompetent strata, respectively. And the mainshock occurred at the Slik ramp which connecting these two detachment, which implicates that the Pishan earthquake is an event caused by independent structural unit. The postseismic deformation mainly occurred on the lower flat as afterslip, and accumulated gradually over time. The moment released after a slip in 5 months corresponds to a sub-M_W6.3 event, and is equivalent to the moment released by the mainshock.
Worldwide, earthquakes exhibiting similar characteristics include the 2015 Gorkha M_W7.8 earthquake in Nepal, the 2005 Kashmir M_W7.6 earthquake, the 1999 Chi-Chi M_W7.6 earthquake in Taiwan, China, and the 1995 Colima-Jalisco M_W8.0 earthquake in Mexico, among others. Conducting detailed analyses of these seismic events provides a valuable entry point for clarifying the structural patterns, stress states, and seismogenic features of foreland fold-and-thrust fault zones. Furthermore, it aids in the in-depth analysis of regional seismogenic models and predicting future seismic trends.
Focusing on the Pishan earthquake, expect settling slip by the folding strata above the upper flat; this phenomenon may also depend on both matter properties and gravitational differences between the upper and lower flats. 1)During the fault deformation, a detachment with low competence and low friction coefficient is unable to accumulate significant stress, resulting in the absence of notable stress drops during frictional sliding and instead manifests as a state of after-slip activity. 2)When the detachment, especially the shallow one, has an undersized gravitational load, it may fail to effectively play a role in detachment, leading to a geological process where fault activity may be altered or inhibited. Occurring at the lower flat, the afterslip of the Pishan earthquake cooperated these two situations. 1)The deeper detachment, located on the Cambrian gypsum, may have a lower friction coefficient compared with the upper detachment. 2)And apparently, the deeper detachment possesses more gravitational load. 3)Plus, stress cannot accumulate to a high level at a flat part of a seismogenic fault. These points may lead to the afterslip release of accumulated stress, mostly on the lower flat, as the postseismic deformation. Therefore, the risk of a major earthquake occurring at the lower flat of the fault may be relatively low.
On the one hand, this phenomenon may cause stress loading on the lower fault ramp or the root fault at a deeper level below the fault flat, increasing the seismic risk in the deep structures. On the other hand, if an earthquake was trigged on the lower ramp, the lower flat above it, which had undergone a slip and released a significant amount of energy, would limit the extent of the rupture.
Furthermore, Cambrian gypsum layers are widely present at depth, which can serve as deep detachment surfaces and lower fault flats at the scale of the study area and its adjacent region. Therefore, whether the seismic activity and energy release pattern of the Slik anticline can represent the seismogenic patterns in the front of western Kunlun, and whether such a pattern can effectively provide a basis for regional seismic hazard assessment, deserves further attention and research.

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THREE-DIMENSIONAL SURFACE COSEISMIC DISPLACEMENTS FROM DIFFERENCING PRE- AND POST-EARTHQUAKE TERRAIN POINT CLOUDS

WEI Zhan-yu, HE Hong-lin, DENG Ya-ting, XI Xi

SEISMOLOGY AND GEOLOGY 2025, 47 (1): 167-188. DOI: 10.3969/j.issn.0253-4967.2025.01.011

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After a major earthquake, in addition to determining the location and magnitude of the earthquake, the analysis of the coseismic displacement and deformation patterns near the seismic rupture zone is equally critical, which is crucial for an in-depth understanding of the seismic rupture process, fault behavior, and the relationship between active faults and topography. Although the geodetic techniques for observing the coseismic displacement field of the earth's surface at various spatial and temporal scales are developing rapidly, obtaining a detailed seismic rupture zone and displacement field remains challenging. Current techniques for obtaining these measurements, including Global Navigation Satellite Systems(GNSS), radar or optical remote sensing, and field observations, have their respective limitations regarding observation density, coverage area, measurement dimensions, and operational efficiency. Recently, the widespread adoption and application of high-precision and high-density topographic observation technologies(such as SfM and LiDAR)have enabled geomorphologists and geologists to capture various Earth surface features with unprecedented spatiotemporal resolution and detail. This has made it possible to map detailed three-dimensional displacement fields.

This paper introduces an Iterative Closest Point(ICP)algorithm that uses pre- and post-earthquake topographic point clouds to determine near-field three-dimensional coseismic surface displacements. The main purpose of developing this algorithm is to quickly provide data on the coseismic displacement field near the seismic rupture zone after a major earthquake, compensating for the deficiencies of existing geodetic measurements or field observations. To test the applicability and workflow of the ICP algorithm for obtaining topographic data through aerial photogrammetry in the Sichuan-Yunnan region, we selected two sets of SfM topographic point cloud data from the Jiaoji River fault on the Daliangshan fault zone. By superimposing the coseismic deformation field to simulate the pre-earthquake and post-earthquake topographic point cloud sets, we explored the accuracy of this method under different grid sizes and point cloud densities. This method can accurately recover the direction and magnitude of the coseismic displacement field under a grid size exceeding 50 meters, with horizontal and vertical accuracies of approximately 20cm and 10cm, respectively, comparable to the positioning accuracy of the topographic point clouds. As the point cloud density and grid window size decrease, the accuracy of this method in recovering co-seismic displacement fields declines.

By analyzing the potential impact of terrain changes such as tree growth, house construction, and river erosion on displacement field recovery, the results show that increasing the grid size allows pre- and post-earthquake point clouds to have sufficient terrain structure for matching, reducing the impact of local terrain changes on displacement field recovery. The grid window size is a trade-off between 1)a large scale with sufficient terrain structure and 2)a smaller scale with finer resolution. The ICP method, utilizing high-precision point clouds from before and after the earthquake, can obtain detailed three-dimensional surface displacement fields near earthquake rupture zones, providing new constraints for shallow fault slip and rupture zone deformation and aiding the study of seismic rupture processes and fault growth.

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SURFACE RUPTURE CHARACTERISTICS OF THE JISHISHAN M_S6.2 EARTHQUAKE ON DECEMBER 18, 2023

LI Lin-lin, JIANG Wen-liang, LI De-wen, JIAO Qi-song, LUO Yi, LI Yong-sheng, TIAN Yun-feng, LI Ying-ying

SEISMOLOGY AND GEOLOGY 2025, 47 (4): 1058-1074. DOI: 10.3969/j.issn.0253-4967.2025.04.20240010

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At 23:59 on December 18, 2023, an M_S6.2 earthquake struck Jishishan County, Linxia Hui Autonomous Prefecture, Gansu Province. The epicenter(35.70°N, 102.79°E) was located in the southeastern segment of the Lajishan fault zone, with a focal depth of approximately 10km. According to the Ministry of Emergency Management, the maximum intensity reached Ⅷ degree, with the NNW-striking long axis of the isoseismal zone consistent with the fault strike. Although moderate in magnitude, the earthquake has caused over 150 fatalities, primarily due to its occurrence at midnight, high population density, poor seismic resistance of housing, and secondary hazards such as debris flows.

Following the event, a comprehensive field investigation was conducted at the epicentral area. Utilizing UAV imagery, digital surface models(DSMs) derived from GF-7 satellite data, and InSAR analysis using Sentinel-1 SAR data, the characteristics of the surface ruptures and the seismogenic structure were examined.

The InSAR results from the ascending orbit of Sentinel-1 revealed that coseismic deformation was dominated by uplift, with a maximum line-of-sight(LOS) displacement of approximately 65mm. The primary deformation zone exhibited an elliptical shape, trending NNW, and extended approximately 10km along the fault strike—consistent with the expected rupture length for an event of this magnitude.

Field surveys and UAV imagery identified a ~1km-long NNW-trending surface rupture east of Yinjiashan Village, which cut across multiple geomorphic units. These ruptures exhibited dominantly thrusting motion with minor right-lateral strike-slip components and were linearly distributed, indicating a tectonic origin rather than landslides or secondary processes. The maximum observed offset reached 8cm vertically and 2cm horizontally.

Digital surface model interpretation from GF-7 imagery revealed several NNW-trending linear structures along the eastern front of the Jishishan Mountains, forming linear topographic scarps and ridges. The observed surface rupture corresponds with one of these structures(F₁₂). Additionally, two local rivers exhibit sharp deflections toward the NNW, controlled by these structures, supporting the interpretation that they are branch faults of the northern Lajishan fault.

According to empirical relationships between magnitude, rupture length, and displacement(Wells & Coppersmith, 1994), an M_S6.2 event is expected to produce a rupture length of approximately 10km. Similar surface rupture lengths(~15km and ~11km) were observed in the 2021 M_S6.1 Biru earthquake. Combined with InSAR-derived deformation extent and the lack of field coverage south of the observed rupture, it is inferred that the surface rupture may extend several kilometers southward along the same structural lineament.

In conclusion, the seismogenic fault responsible for this event is the northern Lajishan fault, comprising multiple NNW-trending branch faults along the eastern front of the Jishishan Mountains. The surface rupture identified corresponds to one of these secondary faults. Despite of the modest scale of the Lajishan fault zone compared to major structures like the Altyn Tagh, East Kunlun, and Qilian-Haiyuan fault zones, and its lack of historical large earthquakes, this event highlights the potential seismic hazard posed by smaller faults under the influence of ongoing crustal uplift and tectonic extension in the northeastern Tibetan plateau.

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COSEISMIC SURFACE RUPTURE OF THE M_S6.8 DINGRI EARTHQUAKE IN XIZANG, CHINA, BASED ON GF IMAGERY INTERPRETATION

QIAO Jun-xiang, SHI Feng, LI An, LI Tao, ZHANG Da, WANG Xin, Gesangdanzhen, SUN Hao-yue

SEISMOLOGY AND GEOLOGY 2025, 47 (3): 789-805. DOI: 10.3969/j.issn.0253-4967.2025.03.20250043

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On January 7, 2025, at 09:05, a M_S6.8 earthquake occurred in Dingri County, Shigatse City, Xizang, China, with a focal depth of 10km and an epicenter located at 87.45°E, 28.50°N, as per data from the China Earthquake Networks Center. Rapid identification of coseismic surface ruptures is crucial not only for determining the seismogenic structure but also for post-earthquake damage assessment and emergency response. Based on the objective geological conditions of the Dingri earthquake-affected area, preliminary interpretation of pre- and post-earthquake high-resolution remote sensing data to delineate the spatial distribution and geometric characteristics of coseismic surface rupture zones before field investigations can effectively guide emergency response teams in rapidly and accurately identifying coseismic surface ruptures and conducting subsequent field surveys. This methodology demonstrates high feasibility and necessity for optimizing field workflow efficiency and ensuring targeted structural analysis of seismogenic faults.

This study utilizes high-resolution imagery from the Gaofen -1 satellite to interpret pre- and post-earthquake images, rapidly obtaining the spatial distribution and geometric characteristics of the coseismic surface ruptures. The seismogenic fault is identified as the Dengmecuo Fault, located in the southwest segment of the Shenzha-Dingjie Rift. The coseismic surface rupture zone is primarily distributed near Gulong Village in the northern and central segments of the Dengmecuo Fault, with discontinuous extensions of approximately 15km, consistent with the location of the pre-existing fault. The coseismic surface rupture zone is tectonically partitioned into three distinct segments based on their geographic distribution: The Nixiacuo and Yangmudingcuo segments situated within the northern fault segment, and the Gurong segment developed along the eastern piedmont front of Gurong Village. These three segments exhibit marked differences in spatial scale and morphological characteristics between remote sensing observations and field investigations. The Nixiacuo segment exhibits linear and continuous coseismic surface ruptures, extending approximately 5km, with prominent linear traces visible in satellite imagery, facilitating clear identification. Field investigations reveal that this segment predominantly develops a series of large-scale tensional fractures and three categories of fault scarps with differential heights, with a maximum coseismic displacement of ~3m recorded. In contrast, both the Yangmudingcuo and Gurong segments exhibit smaller-scale coseismic surface ruptures localized along the eastern graben-bounding basin-range boundary. These secondary ruptures are characterized by minor extensional cracks with limited opening amounts(<1m vertical displacements)and fault scarps, manifesting as dark-gray linear features in remote sensing imagery that coincide with pre-existing rupture traces. Their partial obscuration in spectral signatures renders comprehensive visual interpretation impractical, necessitating field validation for complete delineation. Furthermore, this study identifies an ~10km-long associated surface deformation zone along the eastern Dengmecuo Lake shoreline, exhibiting a structural assemblage of extensional fissures proximal to the mountain front and compressional ridges adjacent to the lakeshore, with concomitant sand boil structures observed within the deformation zone. These extensional features present as dark-toned linear traces paralleling the main surface ruptures, displaying discontinuous arcuate configuration convex toward the mountain front within the mid-fan sector of alluvial fans. The compressional uplift zone west of the extensional belt appears as curvilinear bands with central whitish zones flanked by shadowed margins in imagery, demonstrating enhanced spatial continuity along distal fan margins.

The conclusions of this study exhibit high consistency with previous research based on submeter-level resolution remote sensing imagery, confirming the reliability of remote sensing interpretation. However, interpretations derived from 2m resolution imagery have inherent limitations, including difficulties in identifying small-scale surface ruptures and distinguishing surface deformations of diverse genetic origins. Based on existing research integrated with remote sensing image interpretation and field investigations, the identification capability of coseismic surface ruptures in 2m-resolution remote sensing imagery is fundamentally governed by the three-dimensional geometric parameters of the rupture zone—specifically, rupture zone width, along-strike continuity length, and fault scarp vertical displacement. From the case study of the Dingri earthquake, we hypothesize that GF-1 satellite imagery with 2m resolution is capable of resolving coseismic surface ruptures characterized by a minimum rupture width of 1m, along-strike continuity exceeding 10m, and vertical offset≥1m Furthermore, the composite deformation pattern observed along the eastern shore of Dengmecuo Lake, characterized by rear tensile fractures and frontal thrusting, is interpreted as shallow detachment sliding induced by seismic shaking, representing a secondary associated surface deformation zone rather than direct fault displacement. Therefore, the identification of coseismic surface ruptures necessitates integrating remote sensing interpretation with field investigations, requiring not only the analysis of their geometric configuration and vertical displacement but also a synthetic evaluation of genetic origin based on the geological environment to achieve comprehensive and accurate determination.

This study conducted a detailed interpretation of the coseismic surface rupture zone in the earthquake-affected area using GF-1 image data acquired within 24 hours post-earthquake, rapidly delineating the overall geometry and location of the coseismic surface rupture. This approach effectively supported subsequent field investigations and enhanced the efficiency of earthquake emergency response. Furthermore, rigorous field reconnaissance was carried out to validate the remote sensing interpretation results. The findings demonstrate a high consistency between the interpreted segments of the coseismic surface rupture and field observations, confirming the reliability of the remote sensing interpretation. This highlights the potential of domestic high-resolution satellite data for rapid coseismic surface rupture mapping and seismogenic structure identification, providing a feasible, rapid, and efficient methodology for future emergency response to major earthquakes.

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CHARACTERISTICS OF SEISMICITY AND TECTONIC STRESS FIELD IN THE NORTHEASTERN REGION OF THE PAMIR PLATEAU

CUI Hua-wei, YIN Xin-zhong, CHEN Jiu-hui, GUO Biao, LI Tao, YAO Yuan, LI Shi-ying, JIA Zhen

SEISMOLOGY AND GEOLOGY 2025, 47 (2): 577-596. DOI: 10.3969/j.issn.0253-4967.2025.02.20250047

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The northeastern region of the Pamir Plateau marks the convergence of the Pamir Plateau, the Tianshan Mountains, and the Tarim Basin. This area is associated with high levels of seismic activity and has experienced significant casualties due to several major earthquakes. In this study, earthquakes are relocated using the double-difference relocation algorithm, based on seismic observation reports from the China Earthquake Networks Centre(CENC)covering the period from 2008 to 2023. A total of 916 earthquake focal mechanisms were collected from various institutions and studies, including the GCMT, WWSSN, previous research, and the Xinjiang Earthquake Agency. The magnitudes of these events range from M2.8 to M8.2, and the time span extends from 1902 to 2024. The tectonic stress field was inverted using a spatial-temporal stress inversion algorithm with a 1.0°×1.0° grid, based on these historical focal mechanisms.
The relocated earthquakes are distributed along major tectonic zones situated between the Pamir Plateau, the Tianshan Mountains, and the Tarim Basin, forming several seismic clusters within the study area. Most events have focal depths of less than 30km. Seven cross-sectional profiles were selected to analyze the spatial distribution of seismicity. The regional tectonic stress field is primarily dominated by strike-slip and reverse faulting regimes. The maximum principal stress axes are compressional in a nearly horizontal south-north(S-N)direction, while the minimum principal stress axes are extensional in the east-west(E-W)direction, with either horizontal or vertical plunges. Based on the spatial distribution of seismicity and tectonic features, the study area is divided into several subregions: the central Pamir Plateau and its eastern and western flanks; the collision zone between the Pamir Plateau and the Tianshan Mountains and its surrounding areas; the Tianshan Mountains; and the interior of the Tarim Basin.
Preliminary results of earthquake relocation show that focal depths in the southeastern and northwestern parts of the Qimugen Arc Tectonic Belt are deeper than those within the belt. This is attributed to the subduction of the eastern and northeastern Pamir beneath the Tarim Basin toward the east and northeast. Accordingly, the Moho depth is also greater in these regions. These observations suggest that the Qimugen Arc Tectonic Belt represents a key tectonic boundary, with both the Moho and earthquake depths shallower within the belt than in its southeastern and northwestern margins. Focal depths along the southern margin of the Tianshan Mountains are deeper than those in the adjacent Tarim Basin, which is consistent with a deeper Moho in the former. Similarly, both the Moho and earthquake depths within the Ferghana fault and Piqiang fault zones are greater than those outside these faults along the southern margin of the Tianshan Mountains, indicating that these faults serve as significant tectonic boundaries. An area of sparse seismicity overlaps with the source region of the 1902 Atushi(Kashgar)M_W7.7 earthquake, suggesting that accumulated crustal stress was likely fully released by this event. Seismicity in the Tarim Basin primarily consists of aftershock sequences from the 1996-1999 earthquake clusters and the 2003 Bachu-Jiashi M_S6.8 earthquake. The main contributing factors to seismicity in the Tarim Basin are thought to be its low seismic wave velocity, low crustal density, and brittle crustal properties.
The initial results of the tectonic stress inversion indicate that the central Pamir Plateau is undergoing east-west lateral extension under a strike-slip stress regime, driven by compression from the Indian Plate to the south and obstruction from the Tianshan Mountains to the north. A normal faulting regime in the central grid of the Pamir Plateau is interpreted as a center of expansion or gravitational collapse. The tectonic stress field exhibits significant variation across the flanks of the Pamir Plateau. The R-value, stress regime, and plunge of the maximum principal extension axes show gradual and, in some areas, abrupt changes from the central region to the western and eastern margins, as well as in the collision zones between the Pamir Plateau and the Tianshan Mountains. The Tianshan Mountains continue to uplift due to near S-N compression, displaying a dominant reverse faulting regime. In the Bachu uplift and depression region in the southwestern Tarim Basin, the stress field is characterized by both reverse and strike-slip regimes, likely resulting from differences in crustal velocity, density, and structural composition.

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RESEARCH ON ATTENUATION CHANGES OF SUBSURFACE MEDIA IN THE QILIAN MOUNTAINS REGION BASED ON ACTIVE AIRGUN SOURCE

ZOU Rui, GUO Xiao, SUN Dian-feng, WANG Ya-hong, ZHANG Yuan-sheng, QIN Man-zhong, LIU Xu-zhou, LI Shao-hua, SONG Ting, LIU An-guo

SEISMOLOGY AND GEOLOGY 2025, 47 (4): 1204-1221. DOI: 10.3969/j.issn.0253-4967.2025.04.20240071

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Accurately characterizing stress state changes along active faults in seismogenic zones remains a key challenge in geophysics. Although direct observation of stress evolution in the subsurface is difficult, such changes can be indirectly inferred by monitoring variations in seismic wave parameters—particularly wave velocity and attenuation—to track dynamic alterations in regional stress fields. However, wave velocity changes associated with stress redistribution are typically extremely subtle, requiring high-precision observation systems and highly repeatable seismic sources to be detected reliably.

In recent years, land-based seismic airgun active-source technology has emerged as a promising tool for long-term monitoring of crustal media. Airgun sources offer distinct advantages, including high signal repeatability, strong energy output, long propagation distance, and minimal environmental impact, making them ideal for detecting both static structures and temporal variations in crustal properties. In July 2015, we established the Qilian Mountain airgun active-source system at the Xiliushui Reservoir in Zhangye, Gansu Province, to investigate crustal structure and its temporal changes in the fault zones of the eastern Qilian Mountains.

Previous studies using repeatable sources have largely focused on waveform traveltime variations to detect media changes. However, relatively few studies have explored the application of seismic wave amplitude variations, especially in the context of monitoring attenuation. Non-elastic attenuation, commonly described by the quality factor(Q), captures energy losses due to inelastic behavior and heterogeneities in the medium. It is highly sensitive to factors such as microcrack formation, fluid presence, temperature fluctuations, and phase transitions, making it an important indicator of subsurface physical and mechanical states.

One reason for the limited application of attenuation monitoring is the complexity of amplitude interpretation, as amplitudes are affected by geometric spreading, reflection, refraction, scattering, and other propagation effects. Nevertheless, laboratory studies demonstrate that attenuation is more sensitive than wave velocity to stress-induced changes, and under controlled field conditions—such as fixed source-receiver geometry and waveform consistency—high-precision monitoring of attenuation is feasible.

In this study, we apply the spectral ratio method to waveforms generated by the highly repeatable Gansu Qilian Mountain airgun source to calculate the time-dependent attenuation parameter (t^*) at multiple stations in the eastern Qilian region. We then analyze the temporal variations of t^* across different seismic phases and compare these changes with traveltime variations, as well as with surface environmental variables such as barometric pressure, temperature, and precipitation in Zhangye Ganzhou.

Our results show a positive correlation between attenuation changes and traveltime shifts. At station ZDY27, located near the epicenter of the 2019 Zhangye Ganzhou M_S5.0 earthquake, a relative change in t^* of approximately 0.03 seconds was observed. These findings demonstrate that airgun-based attenuation monitoring is a robust and sensitive method for detecting subsurface stress and property changes. This approach provides an important supplement to existing monitoring methods and enhances our capability for continuous, high-resolution surveillance of crustal media in seismically active regions.

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PRECISE JUDGMENT AND THINKING ON THE 2022 MENYUAN M_S6.9 AND LUDING M_S6.8 EPICENTERS

ZHU Yi-qing, ZHAO Yun-feng, WEI Shou-chun, ZHANG Guo-qing, LIU Fang

SEISMOLOGY AND GEOLOGY 2025, 47 (1): 235-245. DOI: 10.3969/j.issn.0253-4967.2025.01.014

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In 2022, the Menyuan M_S6.9 and Luding M_S6.8 earthquakes occurred successively in the north-south seismic belt of China, both of which caused severe property damage. Prior to these two earthquakes, the China Earthquake Administration conducted multiple ground gravity observations in the North-South seismic zone. It successfully made mid-term predictions based on mobile gravity observation data. The actual epicenters of the two earthquakes were not more than 56km away from the center of the predicted earthquake risk zone in 2022, especially in the precise determination of the epicenter position in 2021 and the distance between the actual epicenter and the predicted epicenter was not more than 10km. This article analyzes ground gravity fields' dynamic evolution characteristics and laws at different temporal and spatial scales before the 2022 Menyuan M_S6.9 and Luding M_S6.8 earthquakes. It reviews the prediction process and basis of these two earthquakes, which is helpful for the study of medium and short-term earthquake prediction.

Overall processing and analysis of multi-source gravity observation data in the north-south seismic zone, obtaining regional gravity field changes based on absolute gravity as the unified benchmark in the measurement area and analysis and study of the dynamic changes of the regional gravity field at different spatiotemporal scales before the Menyuan M_S6.9 and Luding M_S6.8 earthquakes. Further study of the spatiotemporal distribution characteristics and precursor mechanisms of regional gravity field changes will be done by combining geological tectonic dynamic environment and strong regional seismic activity events.

1)Before the Menyuan M_S6.9 earthquake, the gravity change first appeared as a gradient zone of gravity change that was consistent with the direction of the Qilian Mountain fault structure belt and then showed certain four-quadrant distribution characteristics around the epicenter area. The earthquake occurred at the center of the four quadrants of gravity change and near the zero value line of gravity change. 2)Before the Luding M_S6.8 earthquake, the gravity change first showed a gradient zone of gravity change that was consistent with the direction of the Xianshuihe fault structural belt and then showed significant four-quadrant distribution characteristics around the epicenter area. The earthquake occurred at the center of the four quadrants of gravity change and near the zero-value line of gravity change. 3)Gravity data reflects both earthquakes well, and obvious four quadrant distribution characteristics and high gradient zones of gravity changes were observed in the epicenter area and its vicinity before the earthquake, which may be gravity precursor information observed during the earthquake preparation process.

In the past, it was very difficult to accurately determine the location of the three elements of earthquakes(time, location, and magnitude). However, suppose potential strong earthquake epicenters and possible magnitudes are delineated. In that case, the determination of the three elements of earthquakes in the future will become the determination of one element, which will greatly improve the prediction ability of earthquakes The next step is how to carry out earthquake monitoring and tracking work in the identified potential epicenter area and its vicinity, which may help with short-term and imminent prediction. Mobile gravity measurement is the main observation method for exploring earthquake prediction. By establishing a high-density atomic gravimeter absolute gravity observation network or a relative gravity observation network with reasonable absolute gravity control and conducting intensive monitoring, it is possible to reveal the distribution characteristics of underground structures near the epicenter of high-risk areas and extract absolute gravity change signals accompanying source changes during the preparation process of strong/large earthquakes, Develop its application and research in short-term earthquake prediction.

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STUDY ON THE INFLUENCE OF LARGE LOW DIP THRUST FAULTS AND THICK BASINS ON STRONG GROUND MOTION: A STUDY IN KASHGAR AREA, XINJIANG, China

SHEN Zhu-yue, ZHAO Shun, SUN Yao-chong, XU Du-yuan, YU Hou-yun, ZANG Nan, WANG Chun-jing

SEISMOLOGY AND GEOLOGY 2025, 47 (2): 610-626. DOI: 10.3969/j.issn.0253-4967.2025.02.20240158

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Since the Cenozoic era, the Xinjiang region has undergone significant geological evolution, resulting in numerous large-scale low-angle faults and extremely thick sedimentary basins. These unique geological features have profoundly influenced strong ground motion within the area, particularly in regions such as Kashgar, which is situated near the Pamir Plateau. This study focuses on the effects of the Tuomuluo’an Fault and the thick sedimentary layers of the Tarim Basin on seismic activity and the amplification of strong ground motion. Additionally, the Kashgar region’s geographical position south of the Tuomuluo’an front fault further highlights its vulnerability to complex seismic dynamics.
To comprehensively understand these phenomena, researchers developed a series of low-angle thrust fault models, thick sedimentary basin models, and strong ground motion models based on detailed data from the Tuomuluo’an fault system around Kashgar and sedimentary layer characteristics in the Tarim Basin. Numerical experiments were conducted using dynamic simulations of earthquake sources and seismic wave field propagation to analyze how fault dip angle, sedimentary layer thickness and earthquake source location influence strong ground motion.
The numerical experiments revealed several critical insights into the seismic behavior of the region. First, it was found that the Tuomuluo’an fault in the Kashgar region exhibits a greater tendency for earthquake ruptures to reach the surface when occurring along the upper ramp segment. This is due to the specific geometric configuration and stress conditions of this portion of the fault system. In contrast, ruptures along the lower slope are less likely to propagate to the surface, indicating that the fault’s dip angle significantly determines the likelihood of surface-breaking earthquakes. Second, the study demonstrated that the thick sedimentary basin of the Tarim Basin significantly amplifies strong ground motion in the Kashgar region. This amplification occurs because the soft, low-velocity sediments in the basin trap seismic waves and cause prolonged shaking, increasing ground motion intensity during an earthquake. To further investigate this phenomenon, a scenario earthquake was simulated with its nucleation location on the eastern segment upper ramp of the Tuomuluo’an fault. The results generated peak ground velocity and intensity maps essential for disaster assessment and planning.
The simulation revealed that earthquake disasters in the Kashgar area are divided into two distinct regions: one near the seismogenic fault extending along its direction, where strong shaking is expected to be most intense, and another above the Tarim thick sedimentary basin, where ground motion is significantly amplified due to the geological characteristics of basin. Additionally, complex terrain changes influenced earthquake disaster zones, highlighting the importance of topographical factors in determining seismic hazard distribution.
The study concludes that several key factors significantly affect strong ground motion in the Kashgar region: the dip angle and geometric shape of the Tuomuluo’an fault, the thickness of sedimentary layers, and the regional topography. These findings enhance our understanding of seismic hazard assessment in the area and provide valuable insights for disaster preparedness and mitigation strategies. The geological conditions of the Xinjiang region, characterized by large-scale low-angle faults and thick sedimentary basins since the Cenozoic era, further underscore the importance of these findings for regional earthquake risk evaluation.
This research provides critical scientific evidence to improve seismic hazard assessment in the Kashgar region. The study offers practical recommendations for enhancing earthquake preparedness and reducing potential disaster impacts in the Xinjiang region by identifying the key factors that influence strong ground motion.

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DENSE BENDING MOMENT NORMAL FAULT SCARPS ALONG THE GUMAN ANTICLINE AT THE FOOTHILL OF THE WEST KUNLUN MOUNTAINS

XU Jian-hong, CHEN Jie, LI Tao, ZHANG Bo-xuan, DI Ning

SEISMOLOGY AND GEOLOGY 2025, 47 (2): 405-428. DOI: 10.3969/j.issn.0253-4967.2025.02.20240148

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Bending-moment fault and flexural-slip fault are two types of fold-related faults in compressional tectonic environments. Historical earthquake records suggest that both fault types may be active simultaneously, with their fault scarps providing crucial insights into strong seismic events. In the northern region of the Guman anticline, located at the foothills of the West Kunlun Mountains, numerous prominent bending-moment normal fault scarps have developed, reaching heights between 0.5m and 16.0m. This study focuses on a fault scarp segment approximately 5.4km long and 4.2km wide. A digital elevation model(DEM)with a 0.2m resolution was generated using drone photogrammetry. A total of 739 cross-fault scarp profiles were extracted, providing key parameters such as scarp height, slope, displacement continuity, and cumulative displacement trends. Data analysis yielded the following findings:
(1)In the study area, dense bending-moment normal faults align along the active anticline axis, dipping toward the axial plane at angle of 70°~80°, as observed in a trench. Among these faults, more than a dozen dip northward, whereas only 1-2 dip southward, forming asymmetric grabens. This asymmetry may be attributed to the overall northward tilt of the strata and the differing limb structures of the underlying anticline. These faults divide the terrace surfaces into multiple rectangular blocks, 380~650m wide. The blocks exhibit outward tilting relative to the fold axis, with those cut by north-dipping faults tilting southward and those cut by south-dipping faults tilting northward. The degree of tilting and fault displacement is closely related to the thickness of the underlying anticlinal strata and the extent of stratal bending.
(2)Displacement profiles along the faults reveal a step-like decrease in displacement as terrace surfaces become progressively younger, with maximum slope profiles displaying similar trends. This pattern suggests long-term fault activity. Cumulative displacement data confirm this trend, with displacement values of(54.5±3.3)m for terrace T3c and(19.5±1.1)m for terrace T1c. The total displacement of T3c is approximately 2.8 times that of T1c, and displacement ratios across different terraces range from 1.5 to 5.5. Higher ratios indicate greater displacement accumulation on older terraces, suggesting an earlier onset of fault activity. These displacement rankings imply that an initial framework of faults developed in the region, followed by subsequent fault intrusion. Notably, Fault F₈ exhibits a displacement ratio of 5.5, forming a(1.0±0.3)m high fault scarp on the young T1b terrace, indicating that even the earliest-formed faults remain active.
(3)Seismic reflection profiles reveal that the south flank of the Guman anticline dips 3°~6° northward, while the north flank dips 12°~14° northward. The underlying blind thrust exhibits a lower flat-ramp-upper flat geometry. However, bending-moment normal faults are not visible in the seismic reflection data, suggesting that they are secondary structures associated with anticline deformation. The fault zone aligns with the anticline’s fault-bend axis, indicating ongoing activity in the anticline zone. The bending-moment normal faults are rootless, meaning they are not primary seismogenic faults. Instead, they primarily develop in poorly layered strata and are largely independent of the kinematics of fold growth. Their formation is closely tied to the degree of strata bending and the thickness of overlying beds. Despite their shallow nature, the bending-moment normal faults exhibit long-term activity, providing evidence that the underlying anticline remains active. These findings support the interpretation of the Guman anticline as an active fault-bend fold.

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MOMENT TENSOR INVERSION AND SEISMOGENIC STRUCTURE OF THE 2023 M_S5.5 PINGYUAN EARTHQUAKE

XU Ying-cai, GUO Xiang-yun

SEISMOLOGY AND GEOLOGY 2025, 47 (1): 284-305. DOI: 10.3969/j.issn.0253-4967.2025.01.017

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On August 6, 2023, an earthquake with M_S5.5 occurred in Pingyuan County, Dezhou City, in Shandong Province, North China. Around the epicenter of the M_S5.5 Pingyuan earthquake, obvious earthquake tremors were felt through the regions of Hebei, Henan, Tianjin, Beijing etc. This earthquake also broke the historical record of no earthquake with M≥5.0 within 50km of the epicenter and aroused widespread concern of the society and seismologists. It is urgent to carry out the research on strong earthquake seismogenic structures and seismogenic environments in the basin, which is of great significance to strengthen the seismic tectonic environment exploration and earthquake damage prevention in the weak and rare earthquake areas of the North China Plain. Based on the data of the Regional Seismic Networks around the epicenter, moment tensor solution and centroid depth of the M_S5.5 Pingyuan earthquake were determined using the gCAP inversion method, and the stability of moment tensor inversion of the mainshock is evaluated by Bootstrap method. The M_L≥1.0 earthquakes of the M_S5.5 Pingyuan earthquake sequence were relocated using the double-difference relocation method. By simulation method of the relationship between regional stress regime and focal mechanism, the relative shear stress and normal stress of nodal planes from focal mechanism of the M_S5.5 Pingyuan earthquake were obtained. According to the earthquake relocation, the fault plane was fitted, and the seismogenic structure of the earthquake was analyzed. The results indicate: 1)The scalar seismic moment(M₀)of the M_S5.5 Pingyuan earthquake is 1.97Í10¹⁷N·m, while the moment magnitude is M_W5.5, and the centroid depth is 16km. The moment tensor solution(M_rr/M_tt/M_pp/M_rt/M_rp/M_tp)is -0.129/1.194/-0.459/0.009/0.336/0.245, while the double-couple(DC), isotropic(ISO) and compensated linear vector dipole(CLVD) components account for 92.40%, 6.25%, and 1.35% of the full moment tensor solution. The focal mechanism of the double-couple solution shows that the M_S5.5 Pingyuan earthquake is a strike-slip type natural earthquake event with a little normal fault component, with strike/dip/rake of 222°/71°/-156° and 124°/67°/-21° for nodal planes Ⅰ and Ⅱ. The P-axis azimuth is 84° with plunge angle of 30°, indicating the principal compressive stress in the NEE direction in the focal area, basically consistent with the direction of the main compressive stress of the regional tectonic stress in the North China Plain. The best double-couple solutions of focal mechanism obtained by the Bootstrap method are: strike 220.4°±2.49°, dip 71.5°±4.34°, rake -155.9°±3.58° for the nodal plane Ⅰ, and strike 122.2°±2.83°, dip 67.3°±3.17°, rake -20.2°±4.95° for nodal plane Ⅱ, and centroid depth 16.7±1.10km, reflecting the stability and reliability of moment tensor inversion in this paper. 2)After earthquake relocation, the epicenters of the M_S5.5 Pingyuan earthquake sequence mainly show a dominant distribution in the NE-SW direction, with a length of about 15km and a width of about 5km. The epicenter of the M_S5.5 Pingyuan earthquake is located in the southwest segment of the earthquake sequence, and the epicenters of the M_L≥1.0 earthquake are relatively concentrated on the NE side of the main earthquake, while the distribution of the epicenters of the SW side is relatively sparse. The focal depths of earthquakes with M_L≥1.0 are mainly between 8 and 22km, with an average depth of 15.4km. The focal depth profiles demonstrate the fault plane with a dip to the northwest. 3)The regional stress field of North China Craton primarily exhibits NEE-SWW compression and near N-S tensile. The main stress axis direction of the regional stress field is basically consistent with the P-axis of the focal mechanism of the M_S5.5 Pingyuan earthquake. The strike-slip component of the focal mechanism of the M_S5.5 Pingyuan earthquake shows general consistency with the focal mechanism characteristics of the eastern North China Craton. It is also consistent with the E-W compressive and S-N tensile tectonic stress background of the eastern part of the North China Craton, and the small normal components may be related to the tensile movement of the central and western region of Bohai Bay Basin. The relationship between the focal mechanism and contemporary regional stress regime shows the relative shear stress of 0.860/0.689 for nodal planes I and II under the stress field of the Pingyuan region, and the rake of shear stress for the nodal plane I is close to the rake of focal mechanism. The shear stress on nodal plane I of the focal mechanism is relatively high, reflecting that nodal plane I is very close to the fault shape of the optimal release of relative shear stress of the regional stress field, presenting the source property of right-lateral strike-slip with a small amount of normal component. The fault plane fitting also exhibits the mode of fault movement with right-lateral strike-slip. 4)Combined with the previous studies, it is inferred that the nodal plane I of the focal mechanism for the M_S5.5 Pingyuan mainshock is the possible seismic source fault with a dip angle of 71°, and the main seismogenic structure of the Pingyuan earthquake sequence may be a SW-striking blind fault with steep dip to northwest. Under the long-term contemporary principal compressive stress of the tectonic stress field in North China Plain, the M_S5.5 Pingyuan earthquake occurred as a right-lateral strike-slip seismic dislocation with a little normal fault component due to the rupture on the nodal plane with optimum shear stress release. It is suggested that the seismogenic structure of the Pingyuan earthquake may be related to the Lingxian-Guanxian fault, a hidden fault system formed by the northern section of the Guanxian fault and the southern section of the Lingxian-Yangxin fault.

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COSEISMIC DEFORMATION FIELD AND SLIP MODELS OF JANUARY 23, 2024 M_S7.1 WUSHI EARTHQUAKE, XINJIANG, CHINA

YANG Jian-wen, JIN Ming-pei, LI Qing, LI Zhen-ling, YE Beng, LI Jian, ZHANG Ying-feng

SEISMOLOGY AND GEOLOGY 2025, 47 (5): 1382-1395. DOI: 10.3969/j.issn.0253-4967.2025.05.20240027

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According to the official determination of the China Seismic Network, at 02:09 on January 23, 2024, a magnitude 7.1 earthquake occurred in Wushi County(41.26°N, 78.63°E), Aksu Prefecture, Xinjiang, with a focal depth of 22km. The earthquake occurred at the junction of the southern Tianshan Mountains and the Tarim Basin, located between the Keping foreland thrust belt and the Kuqa foreland thrust belt, and was caused by the northward extrusion of the Eurasian Plate by the Indian Plate. The Wushi earthquake is the largest earthquake in the Tianshan seismic belt since the Suusamyr M_S7.3 earthquake in Kyrgyzstan in 1992. It caused casualties and varying degrees of damage to buildings and infrastructure in Wushi and Akqi counties.

As a shallow-source thrust earthquake, the Wushi event has a high efficiency of seismic energy radiation, leading to stronger ground vibrations and building damage than other earthquakes of similar magnitude. In addition, the seismogenic faults of intracontinental thrust earthquakes rarely rupture the surface or produce only short surface rupture zones, complicating studies of the fault structure and rupture mechanism. Further research on the source rupture process is therefore necessary. The earthquake also alters the surrounding stress field and may affect nearby fault activity. Coulomb stress modeling can estimate the relative stress changes and triggering effects in the epicentral region, which is important for understanding seismogenesis and long-term earthquake prediction.

In this paper, using Sentinel-1A ascending and descending satellite imagery, the co-seismic deformation field of the Wushi earthquake is derived. Constrained by ascending and descending orbit deformation data, independent and joint inversions of the earthquake's source slip model are performed to investigate co-seismic deformation and rupture characteristics. Furthermore, Coulomb stress variations at different depths induced by coseismic dislocation are calculated, and relative stress changes as well as the triggering effects on major faults near the epicenter are evaluated. The main findings are as follows:

(1)Based on the coseismic deformation field of the Wushi earthquake obtained using the D-InSAR “two-track method”, the results show clear interference fringes in both ascending and descending orbits. The long axis is distributed roughly along the NE-SW direction, including two deformation zones, though the NW block exhibits stronger deformation than the SE block. The maximum LOS deformation of the ascending orbit is about 0.77m, while that of the descending orbit is about 0.48m. The positive and negative deformation within the same block are consistent between ascending and descending tracks. Combined with the imaging geometry, these results suggest that the deformation is dominated by vertical displacement, consistent with the typical features of thrust-type seismic deformation.

(2)Constrained by the coseismic deformation data of both orbits and applying the SDM layered model, the independently and jointly inverted source slip models indicate upward rupture propagation along the fault from the initial rupture point. The fault dislocation is characterized mainly as left-lateral reverse faulting. The main rupture zone extends about 45km, with primary slip concentrated along a fault plane striking between about 27~72km and dipping between about 2~25km. The largest rupture zone is biased toward the SW of the epicenter, and the local rupture on the SW side(near strike about 55km)may have broken the surface. Parameters of the slip model are broadly consistent. The moment magnitude derived from ascending and descending data is about M_W7.1, and the maximum slip is about 2.1m, located on the fault plane(41.25°N, 78.59°E) at about 10.3km depth.

(3)The coseismic Coulomb stress results reveal significant stress changes near the epicentral region. Stress loading is pronounced on the northeastern section of the Koksal Fault, the central and northeastern sections of the Tuoshigan Fault, the central and southwestern sections of the Maidan-Shayilam Fault, and the central and southwestern sections of the Wensubei(Kuqi)Fault near the epicenter. This indicates that the regional seismic risk requires close attention.

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THE MAXIMUM VERTICAL DISPLACEMENT OF THE M_S6.8 EARTHQUAKE IN XIZANG AND ITS SURFACE DEFORMATION STYLE

ZHANG Da, SHI Feng, LUO Quan-xing, QIAO Jun-xiang, WANG xin, YI Wen-xing, LI Tao, LI an

SEISMOLOGY AND GEOLOGY 2025, 47 (3): 707-717. DOI: 10.3969/j.issn.0253-4967.2025.03.20250041

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On January 7, 2025, at 9:05 AM, a M_S6.8 earthquake occurred in Dingri County, Shigatse City, Xizang Autonomous Region. The epicenter was located at 87.45°E and 28.50°N, with a focal depth of 10 kilometers, as determined by the China Earthquake Networks Center. Regarding the maximum vertical displacement of this earthquake, there are differing opinions due to variations in the reference markers used during field measurements of coseismic displacement or deformation amplitude, as well as divergent understandings of the deformation style of earthquake scarps and pre-existing scarps. Additionally, factors such as the complex structure of the surface rupture zone and the short duration of field investigations contribute to the current discrepancies in understanding the maximum co-seismic displacement. Different scholars have varying perspectives on this matter. To determine the maximum co-seismic displacement and provide data for subsequent research, this study utilized GF1 satellite imagery and drone aerial surveying technology to measure the maximum co-seismic displacement following the earthquake.

The seismogenic fault of the Dingri earthquake is the Dengmecuo Fault. The surface rupture caused by this earthquake is mainly concentrated near Nixiacuo, at the northern end of the Dengmecuo Fault. The surface rupture trace in the Nixiacuo section is evident, striking northeast and arranged in a linear pattern. It develops along the existing steep scar in front of the mountain, cutting through a series of landforms, including alluvial fans and moraines, and aligns well with the original steep scar. This section of surface rupture is large in scale, developing a series of extensional fractures and fault scarps. The surface rupture phenomenon is most pronounced at a location 800 meters north of Nixiacuo, where the largest co-seismic vertical displacement also occurs. At the location of the maximum co-seismic vertical displacement, the main rupture diverges into several secondary ruptures, which later converge back onto the main rupture. Simultaneously, several extensional fractures develop, and a clear vertical displacement is observed between the hanging wall and the footwall, accompanied by rock collapse. This study employed field observations and UAV aerial survey technology to determine the maximum coseismic surface displacement resulting from the Tingri earthquake. Since the surface rupture generated not only vertical displacement but also ground fissures, leading to some horizontal displacement, the displacement could not be measured directly. To address this, we identified two points on the hanging wall and footwall of the fault, measured the distance l between them, and determined the inclination angle θ of l relative to the ground. The vertical displacement was then calculated using the trigonometric relationship l ×sinθ. Four sets of measurements were taken, yielding a result of(2.47±0.1)m. UAV aerial survey technology was used to capture orthophotos of the location with the maximum coseismic vertical displacement. Three profiles were measured, and the largest recorded coseismic vertical displacement was 0.2m.

In this study, we collected empirical formulas derived from the maximum moment magnitude of the Dingri earthquake inverted by other scholars. The calculated maximum co-seismic surface displacement ranged from 2.37m to 2.97m, which is consistent with the(2.47±0.1)m observed in the field and the(2.6±0.2)m obtained using drone aerial survey technology. The moment magnitude of the Yutian earthquake is equal to that of the Dingri earthquake, but its maximum co-seismic surface displacement is smaller than that of the Dingri earthquake. Firstly, the Yutian earthquake exhibited both left-lateral strike-slip and normal fault characteristics, whereas the Dingri earthquake was mainly characterized by normal faulting. Secondly, the Yutian earthquake produced relatively continuous surface ruptures, whereas the Dingri earthquake produced highly discontinuous surface ruptures with significant displacement differences between segments.

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JOINT INVERSION OF THE 2025 DINGRI M_S6.8 EARTHQUAKE RUPTURE PROCESS BASED ON TELESEISMIC P WAVES, STRONG-MOTION AND INSAR DATA

XU Yue-yi, XU Bei-bei, XU Chen-yu, SHAO Zhi-gang, HU Chao-zhong

SEISMOLOGY AND GEOLOGY 2025, 47 (3): 734-746. DOI: 10.3969/j.issn.0253-4967.2025.03.20250033

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At 09:05 Beijing time on January 7, 2025, a M_S6.8 earthquake struck Dingri County, Shigatse City, Xizang Autonomous Region, China, with a focal depth of 10km. The earthquake caused strong ground shaking, reaching a maximum intensity of Ⅸ on the China Seismic Intensity Scale, and resulted in 126 fatalities. This seismic event occurred along the Dengmoco Fault, which is part of the north-south-trending Shenzha-Dingjie normal fault system in the southern Qinghai-Xizang Plateau. The fault extends approximately 60km, dips westward, and has maintained a vertical slip rate of(0.28±0.04)mm/a over the past 1 000 years. Geological investigations indicate that the most recent paleo-earthquake on this fault occurred 4 800-4 968 a BP, with an estimated recurrence interval of(5 500±1 100)a in the Holocene. These characteristics demonstrate that the 2025 Dingri earthquake represents a typical event within the fault’s long-term seismic cycle.

To determine the source mechanism of this event, we performed a joint inversion of the moment tensor using teleseismic P waves and W-phase. By combining the relatively high-frequency P-waveforms with the low-frequency W-phase records, this approach enables a more robust determination of the focal mechanism while providing improved constraints on the centroid location, particularly the centroid depth. The results indicate a moment magnitude of 7.02, with a centroid time offset of 9.7s and a shallow centroid depth of 6km. The optimal centroid is located at(28.6°N, 87.5°E), about 24° east of north from the epicenter. The best-fitting focal mechanism solution yields two nodal planes: Nodal Plane 1 with a strike of 344°, dip of 48°, and rake of -105°; and Nodal Plane 2 with a strike of 185°, dip of 44°, and rake of -74°. Considering the west-dipping geometry of the Dengmoco Fault, Nodal Plane 2 is interpreted as the likely fault plane responsible for the rupture. Based on Nodal Plane 2, we further conducted a joint rupture process inversion using teleseismic P waves, strong-motion waveforms, and InSAR deformation data. The combination of seismic and geodetic observations provided complementary constraints, enhancing both the spatial and temporal resolution of the dynamic rupture process. The results indicate a predominantly normal faulting mechanism with a minor left-lateral component. The rupture propagated mainly northward, with limited southward extension. The rupture lasted approximately 36 seconds, with the main slip occurring between 8 seconds and 24 seconds and concentrated within depths of 0-10km, generating a significant surface rupture approximately 20km north of Changsuo Township. To further explore the fault geometry, we conducted a grid search using a dual-fault model to identify the optimal strike for the northern segment. The analysis identified 240° as the best-fit strike, which slightly improved the overall data fitting and exhibited better consistency with the surface topography. The resulting slip model retained the main rupture characteristics observed in the single-fault scenario. The rupture process can be divided into three stages: ① 0-7s initial nucleation near Cuoguo Township with a relatively minor slip(<1.3m); ② 8-24s primary rupture occurred approximately 20km north of Changsuo, with a peak slip of 4.3m; ③ 25-36s rapid slip attenuation after propagating beyond the northern fault bend.

Our study indicates that the complex fault structure plays a critical role in rupture dynamics. The relatively minor slip observed between Cuoguo Township and Changsuo Township, together with the sparse aftershock activity, suggests the existence of an unidentified east-dipping, NW-trending fault segment in this region. Additionally, the abrupt rupture termination near the northern segment of the Dengmoco Fault is likely influenced by an unrecognized NE-trending subsidiary fault. This study underscores the importance of rupture directivity in seismic hazard assessment and reveals the structural complexity of the Dengmoco Fault system. Overall, the results enhance our understanding of the seismogenic mechanism and contribute to more accurate earthquake hazard evaluations in the region.

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