Abstract:

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.

Key words: Wushi M_S7.1 earthquake, coseismic deformation field, slip model,, Coulomb stress variation

摘要： 2024年1月23日新疆乌什 M_S7.1 地震是自1992年吉尔吉斯斯坦Suusamyr M_S7.3 地震以来发生在天山地震带的最大地震, 对其震源破裂机理和邻区应力变化特征开展研究, 可满足防范地震风险的实际需求。文中基于Sentinel-1A升、 降轨卫星影像数据, 采用D-InSAR技术获取了乌什地震的同震形变场。以升、 降轨同震形变数据为约束, 分别独立和联合反演了该地震的震源滑动模型, 并进一步计算了同震位错引起的周边断裂的库仑应力变化。结果表明: 1)InSAR升、 降轨同震形变场长轴大致沿NE-SW向展布, 均表现出北西盘较强、 南东盘较弱的形变特征。升、 降轨相同盘的形变量正负相同, 结合其成像几何模式, 认为乌什地震同震形变结果显示的形变态势以垂直形变为主, 符合逆冲型地震形变的主要特征。升轨LOS向最大形变量约为0.77m, 降轨LOS向最大形变量约为0.48m。2)分别独立和联合反演的震源滑动模型总体差异不大, 均呈现出从初始破裂点开始沿断层面向上破裂的特征, 断层错动以左旋逆断为主。发震断层主要破裂区长约45km, 最大破裂区偏向于震中西南侧, 且主震西南侧的破裂局部区域(沿走向约55km处附近)可能破裂到了地表。升、 降轨数据联合反演得到的乌什地震的矩震级约为 M_W7.1, 最大滑动量约为2.1m, 位于断层面(41.25°N, 78.59°E)地下约10.3km深度处。3)乌什地震产生的同震库仑应力对震中附近的阔克萨勒断裂东北段、 托什干断裂中段和东北段、 迈丹-沙依拉姆断裂中段和西南段、 温宿北(库齐)断裂中段和西南段具有显著的应力加载作用, 地震形势值得关注。

关键词: 乌什M_S7.1地震, 同震形变场, 震源滑动模型, 库仑应力变化