Three-dimensional velocity structure around the focal area of the 2021 MS6.4 Yangbi earthquake  

作　　者：Yunpeng Zhang Weitao Wang Wei Yang Min Liu Jinbo Su Xiaobin Li Jun Yang 

机构地区：[1]Institute of Geophysics,China Earthquake Administration,Beijing 100081,China [2]Key Laboratory of Earthquake Source Physics,China Earthquake Administration,Beijing 100081,China [3]China University of Geosciences(Beijing),Beijing 100083,China [4]Urumqi Institute of Central Asian Seismology,China Earthquake Administration,Urumqi 830011,China [5]Dali Center,China Seismic Experimental Site,Dali 671000,China

出　　处：《Earthquake Science》2021年第5期399-412,共14页地震学报（英文版）

基　　金：supported jointly by the Special Fund of the Institute of Geophysics,China Earthquake Administration(Grant Nos.DQJB20K36,DQJB19B29,and DQJB20B15);the National Natural Science Foundation of China(Grant Nos.41790462 and 41974069).

摘　　要：On May 21,2021,an MS6.4 earthquake occurred in Yangbi,Yunnan province,China,which exhibited typical foreshock-mainshock-aftershock characteristics.To better understand the velocity structure of the focal area and adjacent fault zones,Pg/Sg travel times at 12 seismic stations for the local earthquakes with ML≥1.5 from 2009-2019 and the Yangbi sequence in May of 2021 were used to invert the three-dimensional(3D)structures for both vP and v_(P)/v_(S).The obtained structure extends deeply to 15 km for area(25°N-26.5°N,99.5°E-101°E)at a horizontal resolution of 10×10 km,and the accuracy of the v_(P) velocity was verified using airgun signals excited by the Binchuan Airgun Transmitting Seismic Station(BATSS).The resulting v_(P) and v^(P)/v_(S) images correlate with existing fault zones and the Yangbi sequence,including:(1)The shallow velocity structure at 0 km agrees with local topography,where the Binchuan basin exhibits low-v_(P) and high-v_(P)/v_(S) values.From 3-15 km,v_(P) and v_(P)/v_(S) show variations,and the boundaries are consistent with the main faults(e.g.,the Weixi-Qiaohou-Weishan,Honghe,and Chenghai faults).(2)The largest foreshock(M_(S)5.6),main-shock(MS6.4),and largest aftershock(M_(S)5.2)occurred near the boundaries where both vP and v_(P)/v_(S) have clear contrasts.(3)Small earthquakes are also concentrated in the transition zone between high-and low-vP and v_(P)/v_(S) anomalies,and are biased toward low-v_(P)/v_(S) zones.(4)Boundaries in v_(P) and v_(P)/v_(S) are observed at 20 km west of the Weixi-Qiaohou-Weishan fault,indicating that there may exist one hidden fault.

关 键 词：MS6.4 Yangbi earthquake Honghe fault Weixi-Qiaohou-Weishan fault body wave tomography air-gun source. 

分 类 号：P315[天文地球—地震学]