2020年西藏定日M_(W)5.6地震震源参数估计和应力触发研究  

Estimated seismic source parameters for 2020 Dingri M_W5.6 earthquake in Xizang and study on the stress triggering

作　　者：李琦[1,3,4] 李承涛 赵斌 黄勇[1,3,4] 万永革 谭凯[1,3,4] 董晴 LI Qi;LI ChengTao;ZHAO Bin;HUANG Yong;WAN YongGe;TAN Kai;DONG Qing(Institute of Seismology,China Earthquake Administration,Wuhan 430071,China;Hebei Key Laboratory of Earthquake Dynamics,Sanhe Hebei 065201,China;Gravitation and Earth Tide,National Observation and Research Station,Wuhan 430071,China;Hubei Earthquake Administration,Wuhan 430071,China;Geological Environmental Center of Hubei Province,Wuhan 430034,China)

机构地区：[1]中国地震局地震研究所,武汉430071 [2]河北省地震动力学重点实验室,河北三河065201 [3]武汉引力与固体潮国家野外科学观测研究站,武汉430071 [4]湖北省地震局,武汉430071 [5]湖北省地质环境总站,武汉430034

出　　处：《地球物理学报》2024年第1期172-188,共17页Chinese Journal of Geophysics

基　　金：中国地震局地震研究所和应急管理部国家自然灾害防治研究院基本科研业务费专项资助项目(IS202236332);国家自然科学基金(42304005);河北省地震动力学重点实验室开放基金项目(FZ212201);湖北省自然科学基金(2021CFB508)联合资助。

摘　　要：2020年3月20日青藏高原西南缘定日县发生M_(W)5.6地震,距2015年尼泊尔M_(W)7.9地震~250 km.尼泊尔地震,尤其是震后余滑是否触发了此次定日地震还有待研究.本文联合合成孔径雷达和区域地震波资料研究定日地震的破裂特征.首先利用近场形变和宽频带地震波资料,通过贝叶斯自举优化算法揭示定日地震的均匀滑动模型;然后在此基础上构建断层几何模型并反演震源滑动分布.研究发现定日地震的发震断层走向~334°,倾角~51°.破裂主要集中在约2.0~5.5 km深度范围内.破裂范围~5.6 km×4.4 km,释放总的地震矩~3.33×10^(17)N·m.最大滑动量~1.27 m,发生在3.786 km深度.破裂以正断滑动为主兼少许右旋走滑分量,同区域历史地震表现出相似的破裂机制,表明印度板块向北东方向挤压欧亚板块,在藏南地区产生了近东西向的张应力.库仑应力变化研究表明,尼泊尔M_(W)7.9地震主余震和定日地区四次历史地震共同触发了2020年定日M_(W)5.6地震,其中尼泊尔地震震后2年的余滑引起的库仑应力变化占库仑应力增加总量的~40%,震后余滑在未来地震危险性评估中发挥的作用不容忽视.The 20 March 2020 Dingri M_W5.6 earthquake occurred in the southwestern margin of the Tibetan Plateau,about 250 km away from the 2015 Nepal M_W7.9 earthquake.Whether the Nepal earthquake,especially the afterslip,triggered the Dingri earthquake remains to be studied.Here,Interferometric Synthetic Aperture Radar(InSAR) and regional seismic data were combined to learn about the rupture features of the Dingri earthquake.We first utilized the near-field displacements together with broadband seismic waveforms to reveal the uniform slip model by using a Bayesian bootstrap optimization nonlinear inversion method.Then,we constructed a fault plane based on the geometrical parameters and inverted the source slip distribution.The study found that the strike of the Dingri earthquake′s fault was ~334° and the dip was ~51°.The rupture range was ~5.6 km×4.4 km,and the total seismic moment released was ~3.33×10~(17) N·m,corresponding to M_W5.6.The peak slip was ~1.27 m,which occurred at a depth of ~3.786 km.The slip was mainly confined between ~2.0 and 5.5 km in depth and was characterized predominantly by normal slip with slight right-lateral strike-slip components,which suggest that the Indian plate compresses the Eurasian plate northeastward,which produces near East-West tension in southern Tibetan Plateau.The study of Coulomb stress change showed that the Nepal M_W7.9 earthquake and its aftershocks,together with four historical earthquakes in Dingri area,triggered the 2020 Dingri M_W5.6 earthquake.The Coulomb stress change caused by afterslip in two years of the Nepal earthquake accounts for ~40% the total Coulomb stress increase,which indicates that the role of the afterslip in seismic risk assessment cannot be ignored.

关 键 词：青藏高原 定日M_(W)5.6地震 合成孔径雷达形变 滑动分布 尼泊尔M_(W)7.9地震 库仑应力变化 

分 类 号：P315[天文地球—地震学] P223[天文地球—固体地球物理学]