InSAR数据约束的2020年西藏定日MW5.7地震源模型及构造意义

doi:10.12196/j.issn.1000-3274.2021.01.009

摘要/Abstract

摘要： 2020年3月20日, 处在北喜马拉雅断裂与申扎—定结断裂交会区的西藏定日发生M_W5.7地震, 此次地震发震断层源模型的研究对于认识该地区的复杂地质构造具有重要意义。本文利用升、降轨Sentinel-1A星载SAR数据, 通过合成孔径雷达干涉测量(InSAR)处理获得了地震引起的地表位移场, 其中, 雷达视线方向(LOS)最大地表位移达到0.16 m。基于均匀弹性半空间位错模型, 利用得到的地表形变数据, 通过非线性和线性反演确定了包含断层几何参数以及滑动分布的震源模型, 最后对发震断层的构造特点进行了分析。结果表明, 发震断层是具有少量右旋走滑分量的浅部隐伏正断层, 断层走向为319°, 倾角为44°, 断层滑动主要集中在1~6 km深的范围内, 最大滑动量位于深度4 km处且达到0.8 m。地震释放的地震矩为4.14×10¹⁷ N·m, 对应矩震级为M_W5.7, 与地震波形反演结果一致。通过分析, 我们认为此次定日地震的发震断层可能为申扎—定结主断裂南端“Y”字型的分支断裂, 该地区“Y”字型构造的存在可能是小震集中于此的主要原因。

关键词: 2020年定日M_W5.7地震, InSAR, 震源模型

Abstract: Dingri Tibet, occurred a M_W5.7 earthquake On March 20, 2020, locating in the geologically complex intersection of Northern Himalayan fault and Shenzha-Dingjie fault. It is very significant to understand the complex tectonic in this area by studying the source model of this earthquake. In this study, use the Sentinel-1A spaceborne SAR data of ascending and descending orbits, to obtaine the surface deformation field caused by the earthquake by synthetic aperture radar interferometry (InSAR). The maximum surface displacement along the line of sight reaches 0.16 m. Based on the uniform elastic half-space dislocation model and the obtained surface deformation data, we determine the source model including the geometric parameters and the slip distribution of the fault by nonlinear and linear inversion. We also analyze the tectonic characteristics of the seismogenic fault. The results show that the seismogenic fault is a shallow blind normal fault with a small amount of dextral strike-slip component. The fault strike is 319° and the dip angle is 44°. The maximum slip occurred at the depth of 4 km and reached 0.8 m. The seismic moment released by the earthquake is 4.14×10¹⁷ N·m, equivalent to M_W5.7 which is consistent with the seismic waveform inversion results. Finally, we consider that the seismogenic fault of the Dingri M_W5.7 earthquake may be a branch fault belonging to a “Y” shaped structure of the middle part of Shenzha-Dingjie fault. The existence of the “Y” shaped structure may be the reason why many small earthquakes concentrate in this area.

Key words: 2020 Dingri M_W5.7 earthquake, InSAR, Source model

中图分类号:

P315.7

王永哲, 陈石, 陈鲲. InSAR数据约束的2020年西藏定日M_W5.7地震源模型及构造意义[J]. 地震, 2021, 41(1): 116-128.

WANG Yong-zhe, CHEN Shi, CHEN Kun. Source Model and Tectonic Implications of the 2020 Dingri M_W5.7 Earthquake Constrained by InSAR Data[J]. EARTHQUAKE, 2021, 41(1): 116-128.

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