Table of Content

20 April 2025, Volume 47 Issue 2

Previous Issue   

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

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

Asbtract ( )   HTML ( )   PDF (7786KB) ( )  

Figures and Tables | References | Related Articles | Metrics

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.

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

CHEN Chang-yun, YIN Hai-quan

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

Asbtract ( )   HTML ( )   PDF (9921KB) ( )  

Figures and Tables | References | Related Articles | Metrics

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.

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

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

Asbtract ( )   HTML ( )   PDF (15306KB) ( )  

Figures and Tables | References | Related Articles | Metrics

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.

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

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

Asbtract ( )   HTML ( )   PDF (11046KB) ( )  

Figures and Tables | References | Related Articles | Metrics

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.

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

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

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

Asbtract ( )   HTML ( )   PDF (6489KB) ( )  

Figures and Tables | References | Related Articles | Metrics

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.

PRELIMINARY STUDY ON THE SEISMOGENIC STRUCTURE OF THE 2024 M5 EARTHQUAKE SWARM IN YULI, TARIM BASIN

LI Jin, DENG Ming-wen, ZHANG Zhi-guang, SUN Ye-jun, YAO Yuan, XU Kai-chi

2025, 47(2):  463-487.  DOI: 10.3969/j.issn.0253-4967.2025.02.20250064

Asbtract ( )   HTML ( )   PDF (9183KB) ( )  

Figures and Tables | References | Related Articles | Metrics

The Tarim Basin, a typical small cratonic basin and the largest inland basin in China, is bordered by three major orogenic belts: the Kunlun, Altun, and Tianshan Mountains. Prior to 2000, seismic activity within the basin was sparse. However, with the ongoing development of oil and gas exploration and extraction after 2000, seismicity began to increase, forming a distinct pattern of earthquake swarms—referred to as the Tarim earthquake swarm. Notably, since 2017, both the frequency and magnitude of earthquakes have risen significantly. Major events include the Kuqa M5.6 earthquake on January 16, 2020, the Shaya M6.1 earthquake on January 30, 2023, and three M5.0 earthquakes in the Yuli-Kuqa area in 2024. The rising seismicity has drawn increasing attention, particularly due to heightened activity in the Yuli region since June 2024, now considered the most seismically active area in both Xinjiang and China.
This study applies the Cut and Paste(CAP)method to invert focal mechanisms for three M5.0 earthquakes and other events above M_L4.0 within the Yuli earthquake swarm. The double-difference relocation method was employed to refine the hypocentral locations of earthquakes above M_L2.0. Furthermore, by analyzing the spatial distribution of smaller events and modeling the regional stress field, the study infers plausible parameters for seismogenic fault planes and investigates the faults responsible for the swarm. Among the 44 earthquakes analyzed, 42 exhibit strike-slip focal mechanisms. Cluster analysis reveals the presence of nearly north-south(NS)oriented nodal planes, consistent with regional strike-slip faulting trends in the NS to NNE direction. The relocated seismic sequence shows a clear division into eastern and western branches, both exhibiting linear NNE-trending patterns. Initially, seismic activity was concentrated in the eastern segment, but both branches demonstrated a northward migration over time. Based on the focal mechanisms, relocation data, and inferred fault plane parameters—combined with known fault structures in the region—it is preliminarily concluded that the Yuli earthquake swarm occurred along two nearly parallel, NNE-trending, right-lateral strike-slip faults: F₁(east)and F₂(west). Both faults are nearly vertical, with F₁ exhibiting a steeper dip. The fault depths are estimated at 20~25km. The previously mapped faults F_Ⅰ18 and F_Ⅰ16 near the Yuli swarm may correspond to the shallow and deep sections of faults F₁ and F₂, respectively. The eastern fault(F_Ⅰ18/F₁) maintains consistent dip characteristics from shallow to deep levels, whereas the western fault(F_Ⅰ16/F₂)displays a gentler dip at depth compared to the surface.
In addition to the Yuli swarm, the Tarim Basin has recently experienced the 2012 Luopu M6.0 earthquake(thrust)and the 2023 Shaya M6.1 earthquake(strike-slip), reflecting diverse faulting mechanisms driven by a common regional tectonic regime. The Luopu event resulted from thrusting of the Bachu Uplift toward the Awati Depression, induced by the ongoing convergence of the Indian and Eurasian plates. In contrast, the Shaya earthquake and the Yuli swarm likely represent secondary strike-slip structures accommodating crustal deformation from northward-directed compressive stress associated with NW- and EW-trending thrust belts in the basin interior. The Yuli earthquake swarm is located in the Yuke region of eastern Tarim, an area rich in oil and gas resources. In recent years, extraction activities have intensified, raising questions about a potential link between these activities and the increased seismicity. Further investigation is required to clarify the relationship between industrial activity and the occurrence of the Yuli earthquake swarm.

EARTHQUAKE SEQUENCE RELOCATION AND SEISMOGENIC STRUCTURE OF THE 2024 M_S7.1 WUSHI EARTHQUAKE ON JANUARY 23, 2024, XINJIANG

WANG Xue-zhu, WU Chuan-yong, LIU Jian-ming, ZANG Ke-zhi, YUAN Hai-yang, GAO Zhan, ZHANG Jin-shuo, MA Yun-xiao

2025, 47(2):  488-506.  DOI: 10.3969/j.issn.0253-4967.2025.02.20240153

Asbtract ( )   HTML ( )   PDF (11676KB) ( )  

Figures and Tables | References | Related Articles | Metrics

At 2:09 on January 23, 2024(Beijing time), an earthquake of M_S7.1 occurred in Wushi County, Aksu region, Xinjiang Uyghur Autonomous Region. This earthquake is the first earthquake with a magnitude greater than 7 in the Tian Shan seismic belt after the 1992 Susamer M7.3 earthquake. This earthquake occurred near the range-front Maidan fault which is the boundary structure between the southern Tian Shan and Tarim Basin. In fault geometry, the Maidan fault shows a complex geometry. On the plane, the Maidan fault comprises multiple roughly parallel secondary faults. On the profile, the gently dipping mountain front fault controls the folding deformation of the late Cenozoic. The front and back mountain faults converge in the deep part. This causes the Tarim Plate to deeply subduct along a large subduction zone under the Tianshan. The thrust-nappe structural system is often composed of multiple fault zones that can generate strong earthquakes because these fault zones converge to the same detachment surface in the deep part. Because a fault zone triggers or suppresses strong seismic activity in adjacent faults after a strong earthquake.
Because the main earthquake did not generate obvious coseismic surface ruptures, there is still a great controversy and uncertainty on its seismogenic structure. Determination of the seismogenic structure is crucial for analyzing the potential location of the next major earthquake. It is of great significance for evaluating the future risk of strong earthquakes in the region and the stress loading and triggering relationships between different faults.
According to the analysis of Google’s high-precision satellite image interpretation results and field inspections, the geometric structure of Maidan is more complicated. The fault is roughly near the ancient stream of Yu Shangu Xi River, and it can be divided into two branches, east and west of the left steps. The faults all show clear signs of activity at the surface. In this study, we utilize the earthquake relocation results to determine the seismogenic structure of the 2024 Wushi event. Our results show that the main shock began to break in the deep and the aftershocks are extended from deep to the part. The deeper focal depth may be an important factor in preventing the coseismic sliding of the Wushi M_S7.1 earthquake from being transmitted to the surface. The seismic sequence is exhibited by the northeast-southwest. The long axis direction is about 55°, and the total length is about 85km. The aftershock sequence is divided into the northeast, middle section, and southwest section. The rupture range of the Wushi M_S7.1 earthquake is about 35km, which is the middle section of the aftershock sequence. The aftershocks in the northeast section are mainly distributed along F_1-1, the aftershocks in the southeast section are mainly distributed along F_2-2 and the aftershocks in the middle section are mainly distributed along F_1-2. The aftershocks of different sections are distributed on different branches, which means that the strong earthquake triggered the adjacent seismic activity, which belongs to a more complicated grade joint rupture earthquake. At the same time, the CAP waveform counter and method was adopted to obtain the focal mechanism. The nodal planes parameters of the best double-couple focal mechanisms are: strike 115°, dip 52° and rake 132° for nodal plane I, and strike 240°, dip 54° and rake 49° for nodal plane Ⅱ, the depth of the centroid is about 17km. Based on the inversion results of the focal mechanism and the spatial distribution characteristics of the earthquake sequence, we believe that nodal plane II is the seismogenic fault plane. Based on the spatial distribution characteristics of the earthquake sequence, the focal mechanism solution, and the geological structure data of the earthquake area, we suggest that the Biedieli-goukou fault is the piedmont branch of the Maidan fault. The upper part of the fault(4~5km)has no rupture, and it still has a strong risk of strong earthquakes in the future. The Wushi M_S7.1 earthquake triggered the Biedieli fault and the Aheqi fault. During the Late Quaternary period, these faults have repeatedly ruptured to the surface of strong earthquake incidents.

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

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

Asbtract ( )   HTML ( )   PDF (7331KB) ( )  

Figures and Tables | References | Related Articles | Metrics

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.

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

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

Asbtract ( )   HTML ( )   PDF (7312KB) ( )  

Figures and Tables | References | Related Articles | Metrics

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.

PN WAVE VELOCITY AND ANISOTROPY TOMOGRAPHY IN THE UPPERMOST MANTLE OF PAMIR PLATEAU AND ADJACENT REGIONS

LIU Jia-xin, PEI Shun-ping, GUO Yi-cun

2025, 47(2):  547-560.  DOI: 10.3969/j.issn.0253-4967.2025.02.20240155

Asbtract ( )   HTML ( )   PDF (13201KB) ( )  

Figures and Tables | References | Related Articles | Metrics

Since the Cenozoic era, the ongoing collision between the Indian Plate and the Eurasian Plate has formed the largest and youngest continent-continent orogenic belt on Earth. The Pamir Plateau, located at the western end of the India-Eurasia collision zone, is one of the most tectonically active and structurally complex regions globally. It is characterized by widespread folds and faults, frequent M≥7.0 earthquakes, and numerous intermediate to deep-focus earthquakes, making it an ideal natural laboratory for studying plate tectonics and orogenic processes. Investigating the velocity and anisotropic structure of the uppermost mantle beneath the Pamir Plateau and its surrounding regions is of great significance for understanding the tectonic deformation characteristics and dynamic mechanisms of continent-continent collisions. The Pn-wave travel-time tomography method is an effective approach for studying the physical properties of the uppermost mantle, it offers several advantages: 1)Pn-wave ray paths are concentrated in the uppermost mantle, and there is a relatively abundant record of arrival times; 2)this method can simultaneously obtain mutually constrained velocity and anisotropy structures of the uppermost mantle; and 3)although it only provides lateral velocity and azimuthal anisotropy information for the uppermost mantle, it offers higher resolution and accuracy, and the results are not influenced by deeper mantle structures. In this study, using 363 414 Pn-wave arrival times recorded from 103 190 events at 471 stations, we performed Pn-wave travel-time tomography to obtain higher-resolution seismic velocity and anisotropy images of the uppermost mantle beneath the Pamir Plateau and adjacent regions compared to previous studies. The tomography results exhibit a clear correlation with geological structures, with the following key findings: 1)Lower Pn-wave velocities are observed in tectonically active regions such as the Pamir Plateau, Tienshan, Hindu Kush, West Kunlun, and Altyn Tagh, while higher velocities are found in stable ancient blocks like the Indian Plate, Tarim Basin, Tajik Basin, Junggar Basin, and Fergana Basin. 2)The India-Eurasia collision has generated strong Pn-wave azimuthal anisotropy. On both sides of the Pamir collision zone, in the Indian Plate, Tarim Basin, and Tajik Basin, the anisotropy axes align with the plate motion directions. In contrast, in the central part of the collision zone, the anisotropy axes are nearly perpendicular to the maximum compressive stress and crustal motion directions. A similar anisotropy pattern is observed on both sides of the Tienshan. Pn-wave velocities primarily reflect the properties of the uppermost mantle, which is predominantly composed of peridotite. Temperature has a more significant influence on velocity than pressure, and temperature variations are closely linked to tectonic activity. Typically, stable cratonic regions exhibit higher Pn-wave velocities, while tectonically active or volcanic regions with significant fluid activity show lower velocities. The velocity differences between active and stable blocks are mainly attributed to temperature variations. Comparing the surface boundary between the Eurasian and Indian Plates with the high-velocity anomalies observed in tomography reveals that the high-velocity anomaly of the Indian Plate extends approximately 200km northward beneath the Tibetan plateau. Pn-wave azimuthal anisotropy is generally attributed to the preferred orientation of olivine crystals caused by mantle deformation. The anisotropy direction of the Indian Plate is predominantly north-south, consistent with its GPS motion and maximum compressive stress directions. From the Tajik Basin to the western Tarim Basin, the fast-axis anisotropy direction gradually shifts from NW to NE, aligning well with the maximum compressive stress and GPS directions. This is primarily due to the simple shear between the crust and upper mantle caused by crustal shortening and uplift, while the lithospheric mantle subducts during intense plate collision. Similarly, in the Fergana Basin, northern Tarim Basin, and Junggar Basin, the anisotropy directions are nearly north-south, consistent with GPS and maximum compressive stress directions. In regions of intense deformation, such as the Hindu Kush, Pamir Plateau, West Kunlun, Altyn Tagh, and Tienshan orogenic belts, the anisotropy directions are perpendicular to the maximum compressive stress directions, indicating strong pure shear deformation in the uppermost mantle. This suggests that in continent-continent collision zones, not only does the crust undergo significant shortening and uplift, but the uppermost mantle also experiences substantial compressional deformation. Finally, we propose an improved dynamic model of continent-continent collision to elucidate the collision process between the Indian Plate and the Tarim and Tajik Basins, as well as the mechanisms of anisotropy formation.

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

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

Asbtract ( )   HTML ( )   PDF (14230KB) ( )  

Figures and Tables | References | Related Articles | Metrics

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.

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

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

Asbtract ( )   HTML ( )   PDF (15713KB) ( )  

Figures and Tables | References | Related Articles | Metrics

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.

COSEISMIC SLIP AND COULOMB STRESS OF THE 2024 M_W7.1 HYUGANADA EARTHQUAKE

YANG Si-yuan, HU Yan

2025, 47(2):  597-609.  DOI: 10.3969/j.issn.0253-4967.2025.02.20240152

Asbtract ( )   HTML ( )   PDF (4237KB) ( )  

Figures and Tables | References | Related Articles | Metrics

In Southwest Japan, the Philippine Sea Plate subducts beneath the Eurasian Plate, which makes it one of the most seismically active areas in the world. This area nucleates primarily thrust-type earthquakes over the subduction interface. On August 8, 2024, a M_W 7.1 earthquake occurred in the Hyuganada region in southwestern Japan, offering a valuable opportunity to investigate the seismic slip of this event. Understanding the seismic slip plays an essential role in evaluating earthquake hazards, because it helps better understand the fault behaviors and stress interactions among active crustal faults and thus potential seismic impacts.
In this study, we first derived the coseismic displacements caused by the earthquake through Global Navigation Satellite System(GNSS)data. The maximum horizontal displacement is approximately 15cm, decreasing rapidly as the distance from the rupture zone increases. The vertical displacement shows distinct spatial characteristics. In the southeastern area of the Kyushu Island, near the rupture zone, the subsidence is predominant, with a maximum subsidence of about 6cm. Northwest of this area, the displacement gradually changes to uplift. This result indicates a complex deformation from the rupture area to the farther areas. Based on the elastic half-space model, we inverted the coseismic slip distribution using the derived GNSS displacements. In the model, we have considered a rupture fault with a length of 100km and a width of 60km. This fault is divided into 220 small rectangular elements, with 20 elements in the length direction and 11 in the depth direction. The length of each small rectangular tile is fixed at 5km, while the tile width varies with the depth. The minimum width is 5.2km, and the width increases with depth according to a proportionality coefficient of 1.01. We further use the grid search method to determine the fault dip angle and strike direction. The dip angle and strike direction of the fault are varied within ranges of -50° to 100° and 100° to 300°, respectively. Through these processes, the optimal fault dip angle and strike direction are determined to be 24° and 206°, respectively, consistent with the focal mechanism by the United States Geological Survey(USGS). The inverted coseismic slip distribution shows that the slip is primarily concentrated at 5~20km depths, featuring an elliptical pattern with a maximum slip of 1.47m. Based on the inverted fault slip model, we calculated the surface displacement using Okada’s half-space elastic dislocation theory. The results show that the model reproduces the first-order pattern of GNSS observations in both the horizontal and vertical directions. The total released moment is about 5.49×10¹⁹ Nm, corresponding to a moment magnitude of 7.09(assuming a shear modulus of 30GPa), which is close to the USGS of M_W7.1.
We calculated the Coulomb stress over the main fault using the inverted coseismic slip model. During this process, we assumed that the frictional coefficient of the fault, shear modulus, and Poisson’s ratio are to be 0.4, 30GPa, and 0.25, respectively. The fault plane’s strike, dip, and slip angles are set to be 206°, 24°, and 76°, respectively. The results reveal that outside the rupture zone, the Coulomb stress is positive, with a peak value of approximately 0.95MPa. In contrast, the overall stress is negative within the rupture zone, especially at depths between 7km and 17.5km, where it reaches a maximum value of -2.03MPa. Furthermore, the analyses on normal and shear stresses reveal a distinct pattern. In the shallow portion of the coseismic rupture zone, spanning from 0km to 7km, the normal stress is positive, with its maximum value reaching approximately 0.30MPa, whereas the shear stress is negative, peaking at around 0.73MPa. In other regions over the fault, the normal and shear stresses exhibit an increasing or decreasing trend.
In addition, we have also investigated the aftershocks that occurred within one month after the earthquake, using data from the USGS and JMA(Japan Meteorological Agency). The location of these aftershocks features a depth range of 10~60km. To further investigate the mechanisms of the aftershock occurrence, we analyzed the distribution of maximum shear stress at a depth of 40km. The results show that aftershocks mainly occur in areas where the shear stress is more than 100kPa. The majority of aftershocks concentrate in areas with the shear stress larger than 500kPa. This suggests at least hundreds of kPa are required to induce aftershocks of this event
To summarize, we have derived the coseismic slip and induced Coulomb stress of the 2024 Hyuganada earthquake. This reveals the seismic slip characteristics as well as impacts on the stress states and aftershock activities, which may contribute to further earthquake hazard assessment and mitigation strategies in the region.

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

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

Asbtract ( )   HTML ( )   PDF (9504KB) ( )  

Figures and Tables | References | Related Articles | Metrics

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.

EARTHQUAKE CASUALTY RISK ANALYSIS UNDER THE RECURRENCE SCENARIO OF THE 1902 ARTUX M_S8¼ EARTHQUAKE: A CASE STUDY OF KASHGAR AND ARTUX

NIE Wen-yu, FAN Xi-wei, LI Hua-yue, QI Yuan-meng, LIU Min

2025, 47(2):  627-648.  DOI: 10.3969/j.issn.0253-4967.2025.02.20240156

Asbtract ( )   HTML ( )   PDF (16445KB) ( )  

Figures and Tables | References | Related Articles | Metrics

Despite global efforts to reduce earthquake disaster risk, earthquakes remain one of the most destructive natural disasters in the world. Since precise earthquake prediction remains beyond human capability, conducting accurate earthquake casualty risk assessment has become one of the most feasible and effective strategies to reduce human losses. Kashgar and Artux are located in the southwestern part of the Xinjiang Uygur Autonomous Region, on the western edge of the Tarim Basin. These are two important cities in northwest China, situated in the Pamir tectonic knot region of the India-Eurasia continental collision zone, one of the world’s most seismically active regions due to intracontinental subduction. Historically, this region has experienced multiple major earthquakes, with the most representative example being the 1902 Artux earthquake, which had a magnitude of M_S8¼. This earthquake caused severe casualties and highlighted the region’s high susceptibility to seismic hazards. In this study, we used the historical seismic intensity scenario of the 1902 Artux earthquake as a deterministic earthquake scenario to understand the potential impact of a similar event under contemporary conditions. First, using time-series mobile signaling data and machine learning methods, we extracted the function types of buildings in the study area and developed a thematic dataset of building function types. Utilizing the extracted building function types, high-resolution population heatmap data, and a mapping method between grids and individual buildings, we allocated the population within the grids to specific buildings. Subsequently, by considering the relationships among building function types, temporal characteristics, local daily activity patterns, and indoor occupancy rates, we determined the spatial distribution of the indoor population in the study area. Understanding the potential damage levels of buildings under specific seismic scenarios is crucial for predicting casualty risks and formulating effective emergency response strategies. Therefore, a quantitative analysis of building damage levels under the deterministic earthquake scenario was conducted to clarify damage distribution for buildings in specific intensity scenarios. Subsequently, based on building vulnerability analysis methods, we estimated the daytime and nighttime fatality risks under the recurrence of the Artux earthquake at a 30″grid scale. The results indicate that if the 1902 M_S8¼ Artux earthquake were to recur, areas with high risk of fatalities would mainly be concentrated in the densely populated urban centers of Kashgar and Artux, where buildings are densely packed, populations are concentrated, and some structures lack adequate seismic resistance. The risk of casualties is higher at night than during the daytime. To evaluate the effectiveness of population heatmap data in earthquake casualty assessment, this study compared the evaluation method based on population heatmap data with the method using the Seventh National Census data. The results demonstrate that traditional census data can only provide a rough estimate of casualties based on administrative divisions. However, its reliance on administrative boundaries means it lacks the spatial detail necessary to accurately depict casualty distribution and presents scale inconsistencies that hinder effective risk comparisons across different areas. In contrast, the assessment method based on population heatmap data enables spatial visualization of fatality risks through optimized scaling and establishes a uniform spatial comparison benchmark, thereby providing strong support for the precise allocation of emergency rescue resources. By introducing high-resolution population heatmap data and a thematic dataset of building function types, this study has enhanced the accuracy and practicality of earthquake casualty risk assessment. The results not only reveal the potential for high human casualties if a historical earthquake were to recur today but also demonstrate the distribution characteristics and temporal differences in high-risk zones, emphasizing the importance of considering temporal factors in disaster mitigation strategies. These insights provide robust scientific support for developing precise disaster mitigation and preparedness strategies in earthquake-prone urban areas.

Research Briefs

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

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

Asbtract ( )   HTML ( )   PDF (13633KB) ( )  

Figures and Tables | References | Related Articles | Metrics

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.