Coseismic Deformation and Fault Slip Distribution of the January 7, 2025, Dingri MW7.1 Earthquake
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摘要:
2025年1月7日西藏自治区日喀则市定日县发生MW7.1地震，震中位置位于申扎‒定结裂谷断系南端和藏南拆离系断裂的交汇处，靠近登么错断裂.为深入了解此次地震的发震机制、滑动分布以及库仑应力扰动，首先利用Sentinel-1A数据，通过InSAR及POT测量技术获取其同震形变场信息；然后，利用SDM程序进行断层滑动分布反演，继而计算不同深度的同震库仑应力扰动.研究结果表明：定日地震同震变形以地表沉降为主；发震断层走向近南北，断层倾角约60°；断层滑动分布反演表明主要破裂区域（滑动量 > 1 m）的长度约40 km、宽度约14 km；最大滑动量约4.45 m，位于断层深度约4.33 km；平均滑动角约-76.81°，表明此次地震是一次以正断破裂为主兼具略微左旋走滑的事件；当剪切模量取30 GPa时，反演的地震矩约3.53×1019 N·m，相当于矩震级MW7.0.早期余震主要分布于主破裂区域外围.另外，同震与震后库仑应力扰动表明，申扎‒定结断裂南端、札达‒拉孜‒邛多江断裂东侧、达吉岭‒昂仁‒仁布断裂中部及东侧、与雅鲁藏布江断裂中部的库仑应力增加明显大于阈值10 kPa，其未来地震风险值得关注.
Abstract:On January 7, 2025, an MW7.1 earthquake struck Dingri County, Shigatse City, Xizang Autonomous Region. The epicenter was located at the intersection of the southern segment of the Shenzha-Dingjie rift fault system and the South Tibetan detachment system, near the Dengmocuo fault. To investigate the seismogenic mechanism, slip distribution, and Coulomb stress disturbances of the earthquake, this study firstly utilized the Sentinel-1A data to obtain the coseismic deformation fields by InSAR (interferometric synthetic aperture rader) and POT (pixel offset tracking) techniques. Then, we employed the SDM program to invert the fault coseismic slip-distribution, and subsequently calculated the coseismic Coulomb stress disturbances with variable depth. The results indicate that the coseismic deformation of the Dingri earthquake is dominated by subsidence. The seismogenic fault strikes nearly north-south, with a dip angle of ~60°. The inverted coseismic slip-distribution suggests that the major rupture zone (slip > 1 m) extends ~40 km in length and ~14 km in width. The maximum slip is approximately 4.45 m, occurring at a depth of ~4.33 km. The average rake angle is approximately ‒76.81°, indicating that this earthquake was predominantly a normal faulting event with a slight left-lateral strike-slip component. Taken the shear modulus at 30 GPa, the inverted seismic moment is about 3.53×1019 N·m, equivalent to the moment magnitude MW7.0. Aftershocks predominantly happened around the periphery of the major slip zone. Additionally, the coseismic and postseismic Coulomb stress disturbances suggest significant increases (> 10 kPa) in the southern segment of Shenzha-Dingjie fault, the eastern segment of Zanda-Lhaze-Qongdojiang fault, the central-eastern segment of Dagyiling-Ngamring-Rinbung fault, and the central segment of Yarlung Tsangpo fault. The future seismic hazards on these fault segments warrant heightened attention.
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Key words:
- Dingri /
- earthquakes /
- InSAR /
- POT /
- fault slip distribution /
- Coulomb stress /
- hazards
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图 1 定日MW7.1地震构造背景
震源机制椭球分别来自GCMT，CENC，USGS；红色线条为POT测量解译的发震断层地表迹线；蓝色虚线方框代表InSAR升轨A12与降轨D121数据覆盖区域（数据见表 2）；图中黑色圆圈表示自2015年尼泊尔地震之后至2025年定日地震发生之间，研究区内发生的5级以上的地震.断层编号及名称如下：F1. 藏南滑脱拆离系断裂；F2. 申扎‒定结断裂；F3. 登么错断裂；F4. 当惹雍错‒许如错断裂；F5. 札达‒拉孜‒邛多江断裂；F6. 达吉岭‒昂仁‒仁布断裂；F7. 雅鲁藏布江断裂.断层数据来自徐锡伟等（2016）
Fig. 1. Tectonic setting of the Dingri MW7.1 earthquake
图 2 定日地震同震形变场
a~b分别是InSAR和POT测量获取的升轨形变场；c~d分别是InSAR和POT测量的降轨形变场；红线为同震变形场解译的发震断层；棕色线为石峰等（2025）野外测量的发震断层地表迹线；红色五角星表示GCMT震中位置
Fig. 2. Coseismic deformation field of the Dingri earthquake
图 3 同震形变剖面
a，c，e分别为升轨形变场的AA'、BB'、CC'形变剖面；b，d，f分别为降轨形变场的AA'、BB'、CC'形变剖面；红线表示InSAR测量值，蓝线表示POT测量值；POT可以更好地测量断层近场变形信号；剖面线位置见图 2；红色垂线表示发震断层所在的位置
Fig. 3. Coseismic deformation profile
图 4 断层倾角、光滑因子与数据加权比搜索
a为断层倾角与反演残差之间的关系曲线；b为应力光滑因子与正规化反演残差、正规化对数粗糙度之间的折中曲线；c为POT/InSAR数据加权比与正规化反演残差之间的折中曲线；红色五角星代表参数最优解
Fig. 4. Search for fault dip angle, smoothing factor, and data weighting ratio
图 5 定日地震同震滑动分布
图中箭头表示断层滑动角；红色五角星表示精定位的主震震中；黑色圆点代表余震分布；余震精定位数据来自 杨婷等（2025）
Fig. 5. Coseismic slip distribution of the Dingri earthquake
图 6 同震形变观测值、模拟值以及反演残差
a~c分别代表A12条带的InSAR观测值、模拟值与反演残差；d~f分别代表A12条带的POT观测值、模拟值与反演残差；g~i分别代表D121条带的InSAR观测值、模拟值与反演残差；j~l分别代表D121条带的POT观测值、模拟值与反演残差
Fig. 6. Coseismic deformation observations, simulated values, and inversion residuals
表 1 不同机构与学者给出的震源机制解
Table 1. Focal mechanism solutions provided by different institutions and scholars
来源 纬度(°N) 经度(°E) 深度(km) 走向(°) 倾向(°) 滑动角(°) 滑动深度(km) 最大滑动量(m) 最大滑动量深度(km) 地震矩(N·m) 震级 CENC 28.5 87.45 10 182 22 ‒64 - - - - MS6.8 334 71 ‒100 USGS 28.604 87.378 10 187 49 ‒78 - - - 4.749×1019 MW7.1 349 42 ‒103 GCMT 28.56 87.47 12 173 48 ‒92 - - - 5.29×1019 MW7.1 356 42 ‒88 杨建文等(2025) - - - 184 55 ‒64.75 0~15 4.25 8.6 - MW7.06 王楠等(2025) - - - 187 40 - 1~6 6 - - MW7.1 李雨森等(2025) - - - 189.33 52.8 ‒95.75 0~14 4.73 2~3 6.43×1019 MW7.17 Yu et al.(2025b) - - - 189.2 40.6 ‒82.81 0~10 4.6 - - MW7.1 Yu et al.(2025a) - - - 187 55 - 2~12 6.8 - 4.77×1019 MW7.1 本研究 - - - 185.03 60 ‒76.81 0~15 4.45 4.33 3.53×1019 MW7.0 
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表 2 Sentinel-1A数据
Table 2. Sentinel-1A data
Path 主影像日期 辅影像日期 模式 A12 2025‒01‒05 2025‒01‒17 升轨 D121 2025‒01‒01 2025‒01‒13 降轨
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表 3 分层地壳模型
Table 3. Stratified crust model
分层(km) VP(km·s‒1) VS(km·s‒1) 密度(kg/m3) eta1(Pa·s) eta2(Pa·s) alpha 0~34.49 6.00 3.52 2 720 0 0 1.0 34.49~51.04 6.30 3.68 2 790 0.1×1019 0.1×1020 0.5 51.04~68.98 6.60 3.82 2 850 0.1×1019 0.1×1020 0.5 ≥68.98 8.36 4.63 3 420 0 0.1×1021 1.0 注：中下地壳黏滞系数来自 Chen et al. (2024) ; 其他参数来自Crust1.0 (Laske et al., 2013 ).VP为P波传播速度，VS为S波传播速度，eta1为瞬态黏度，eta2为稳态黏度；alpha=μK/(μK+μM)，其中μK与μM分别表示开尔文体黏滞系数和麦克斯韦体黏滞系数.
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表 4 接收断层参数
Table 4. Receiver fault parameters
断层 走向(°) 倾角(°) 滑动角(°) 藏南滑脱拆离系断裂（F1） 45~180 45 ‒103 申扎‒定结断裂(F2) 203~210 45 ‒46 当惹雍错‒许如错断裂(F4) 0 69 ‒16 札达‒拉孜‒邛多江断裂(F5) 90 45 0 达吉岭‒昂仁‒仁布断裂(F6) 90 45 0 雅鲁藏布江断裂(F7) 90 45 ‒90 注：断层数据来自于 徐锡伟等(2016)；登么错断裂(F3)在此次地震事件中发生破裂，短期内再次发生强震的风险较低，故不计算它的库仑应力扰动.
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