2019年秘鲁北部M7.8地震的矩张量解与破裂过程快速反演

Fast Inversion of Focal Mechanism and Rupture Process of 2019 M7.8 Earthquake in Northern Peru

2019年5月26日(北京时间)秘鲁北部发生M7.8地震,震源深度为100km。本文利用国际地震学研究联合会数据管理中心(IRIS/DMC)提供的远场波形数据,通过波形反演方法快速反演得到此次地震的矩张量解和破裂过程。W震相快速矩张量解反演结果表明此次地震是一次中深源正断层型地震事件,可能是由于正在向下俯冲的纳斯卡板块产生规模巨大的伸展变形所致。远震体波反演有限断层模型结果显示此次地震的发震断层为高倾角的NNW向断层面,破裂从初始破裂点开始,由震中主要向NNW方向延伸破裂,最大滑移量约3m;地震破裂时间约为70s,在40~60s时释放了整个地震80%的地震矩能量,主要破裂区域在震后40s后才开始形成,在40s之前,破裂的集中程度和地震矩释放的规模均较弱,断层在破裂开始后逐渐加速破裂,约50s时地震矩释放速率达到峰值,60s后破裂迅速愈合。

AM7.8 earthquake occurred at the focal depth of 100km in the northern Peru on May 26,2019(Beijing Time).The focal mechanism and rupture process of the earthquake are determined rapidly by using the waveform inversion method with far-field body waveform data downloaded from Incorporated Research Institutions for Seismology(IRIS).The fast focal mechanism determination using W-phase method indicates that the earthquake is a normal fault-type with a intermediate-depth,which is generated within the Nazca plate as a result of internal deformation within the subducting plate.By performing finite fault slip inversion with teleseismic P waves,we find that the nodal plane(strike=349.0°,dip=61.0°)fits the data well after comparing waveform fits based on the two planes of the focal mechanism solution,and most of the rupture slips concentrated in the northwest of the hypocenter with the maximum slip of 3m.The source-time function with a duration of 70s suggesting that over 80%of the moment release occurred during the period of 40s to 60s after the rupture initiation.The concentration of rupture and the size of moment release were weak within the first 40s,then peak slip rate reached the maximum,and after 60s the rupture healed quickly.