四川泸定地区三维速度结构与精定位研究  

Three-dimensional velocity structure and relocation of earthquakes in Luding area,Sichuan Province

作　　者：蔡明远 陈继锋[1] 尹欣欣[1,2] CAI Mingyuan;CHEN Jifeng;YIN Xinxin(Lanzhou Institute of Seismology,CEA,Lanzhou 730000,Gansu,China;Institute of Geophysics,CEA,Beijing 100081,China)

机构地区：[1]中国地震局兰州地震研究所,甘肃兰州730000 [2]中国地震局地球物理研究所,北京100081

出　　处：《地震工程学报》2023年第3期552-564,共13页China Earthquake Engineering Journal

基　　金：甘肃省科技计划(21JR7RA795,21YF5FA031)。

摘　　要：基于四川数字地震台网记录到的该研究区域(27.5°~31.5°N,100°~104°E)103 990个地震的震相数据,运用双差层析成像方法对泸定MS6.8地震震源区及周边地区执行地震层析成像和精定位。结果表明:(1)余震序列主要分布于鲜水河断裂西南侧,长度约60 km,整体沿鲜水河断裂呈北西向展布,震源深度多集中在5~15 km,呈现出由北向南逐渐加深的迹象。根据余震序列空间分布特征及主震位置,提出鲜水河断裂东南段为发震断层,并且发现余震序列南北两端或许存在分支断层。根据背景地震的空间分布特征,推断其或许为泸定主震的前震。(2)主震的西北侧存在高速异常体,其或许阻挡了泸定地震向西北向破裂,结合鲜水河断裂东南段力学性质较弱,其滑动方向为首选的传播方向,推断泸定地震为单侧破裂,方向为东南。(3)泸定地震震源区下方30 km深度处存在弱S波低速层和高波速比,已有结果得知研究区中下地壳存在明显的高导层和低阻层,泸定主震位于热流值为65 mW·m^(2)的大地热流等值线附近,综合推断震源区下方30 km或许存在地壳流体。同时,泸定地震发生在应力易积累,同时又易释放,发生破裂的高低速交界处,推断泸定主震在震源区积累大量应力,加之地壳流体流入发震断层,致使发震断层的弱化,两者共同作用最终引发了泸定MS6.8地震的发生。This work applies the double-difference tomography method for the tomography and relocation of earthquakes in the source area of Luding M S6.8 earthquake and its surrounding areas using the seismic phase data of 103990 earthquakes(27.5°-31.5°N,100°-104°E)recorded by Sichuan digital seismic network.Results show that:(1)the aftershock sequence is mainly distributed on the southwest side of the Xianshuihe fault in the NW direction,with a length of about 60 km.The focal depths are mostly concentrated at 5-15 km and exhibit symptoms of increasingly deepening from north to south.On the basis of the spatial distribution of the aftershock sequence and the location of the mainshock,the southeast section of the Xianshuihe fault is proposed as the seismogenic fault.In addition,branch faults may have occurred at the northern and southern ends of the aftershock sequence.(2)On the basis of the spatial distribution of background earthquakes,foreshocks of the Luding mainshock are speculated to have occurred.The high-velocity anomaly body on the northwest side of the mainshock may block the NW-trending rupture of the Luding earthquake.Given the weak mechanical property of the southeast section of the Xianshuihe fault,the Luding earthquake is inferred to have ruptured unidirectionally in the SE direction.(3)A weak S-wave low-velocity layer and a high-wave velocity ratio are found at a depth of 30 km below the focal area of the Luding earthquake.Previous studies found a high-conductivity layer and a low-resistivity layer in the mid-lower crust of the study area.The mainshock is located near the earth heat flow isoline with a heat flow value of 65 mW·m^(2),so fluid may be found in the crust at 30 km below the focal area.Furthermore,the Luding earthquake occurred at the junction of high and low velocities where stress is easy to accumulate and release,resulting in rupture.A large amount of stress might have accumulated in the focal area,and the fluids in the crust flow into the seismogenic fault,weakening the fault.Finally,the c

关 键 词：泸定MS6.8地震 地震精定位 双差层析成像 地壳流体 鲜水河断裂 

分 类 号：P319.56[天文地球—固体地球物理学]