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
• 来源期刊: 地震学报（英文版）
• 年，卷（期）: 2021,（5）
• 页码范围: 399-412
• 页数: 14页
• 语种: 英文
• DOI: 10.29382/eqs-2021-0033

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 vP/vS.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 vP velocity was verified using airgun signals excited by the Binchuan Airgun Transmitting Seismic Station(BATSS).The resulting vP and vP/vS 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-vP and high-vP/vS values.From 3-15 km,vP and vP/vS 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(Ms5.6),main-shock(Ms6.4),and largest aftershock(Ms5.2)occurred near the boundaries where both vP and vP/vS have clear contrasts.(3)Small earthquakes are also concentrated in the transition zone between high-and low-vP and vP/vS anomalies,and are biased toward low-vP/vS zones.(4)Boundaries in vP and vP/vS are observed at 20 km west of the Weixi-Qiaohou-Weishan fault,indicating that there may exist one hidden fault.