川滇交界东段昭通、莲峰断裂带的深部结构特征与2014年鲁甸M_S6.5地震  

Deep structure of the Zhaotong and Lianfeng fault zones in the eastern segment of the Sichuan-Yunnan border and the 2014 Ludian M_S6.5 earthquake

作　　者：李大虎 丁志峰[2] 吴萍萍[3] 梁明剑[1] 吴朋 顾勤平 康清清[4] LI DaHu;DING ZhiFeng;WU PingPing;LIANG MingJian;WU Peng;GU QinPing;KANG QingQing(Sichuan-Yunnan Earthquake Prediction Experimental Site,Sichuan Branch,Chengdu 610041,China;Institute of Geophysics,China Earthquake Administration,Beijing 100081,China;Institute of Disaster Prevention,Langfang Hebei 056201,China;Earthquake Administration of Jiangsu Province,Nanjing 210014,China)

机构地区：[1]川滇国家地震预报实验场四川分中心,成都610041 [2]中国地震局地球物理研究所,北京100081 [3]防灾科技学院地震科学系,河北燕郊056201 [4]江苏省地震局,南京210014

出　　处：《地球物理学报》2019年第12期4571-4587,共17页Chinese Journal of Geophysics

基　　金：国家自然科学基金项目(41974066,41704055);中国地震局地震科技星火计划(XH20051,XH15040Y);四川省地震局地震科技创新团队项目(201804)共同资助

摘　　要：2014年鲁甸M S6.5地震位于川滇菱形块体向东突出的过渡变形区大凉山次级块体南东缘的昭通、莲峰断裂带内部,属于青藏高原东南缘南北地震带的中南段,近十多年来,该断裂带及其周边中强地震的发生频次明显增多,昭通、莲峰断裂带是否具备孕育和发生强震的深部构造背景成为一个亟待研究的问题.为了研究昭通、莲峰断裂带的深部结构特征及孕震背景,探求2014年鲁甸M S6.5地震的成因的深部动力机制,本文充分收集了四川、云南等区域数字地震台网和“中国地震科学台阵探测-南北地震带南段”(“喜马拉雅”项目Ⅰ期)流动地震台阵的观测数据,应用区域震和远震联合反演的方法得到川滇地区三维速度结构图像,在此基础上重点剖析和研究了昭通、莲峰断裂带P波速度结构;再对昭通、莲峰断裂带及周边区域的重力、航磁数据进行三维视密度和视磁化强度反演,得到了壳内不同深度层视密度的横向变化特征和反映壳内磁性物质的分布范围以及结晶基底的视磁化强度异常分布情况,综合分析研究昭通、莲峰断裂带的深部结构特征及孕震动力环境.研究结果表明:川滇交界东部昭通、莲峰断裂带及其周边地区上地壳物质存在显著的横向介质差异,中下地壳深度范围大凉山次级块体西南缘存在低速异常分布,并呈现出近SN向的展布特征,2014年鲁甸M S6.5地震位于该高低速异常的分界线附近略偏向高速体一侧.P波速度结构还揭示了鲁甸M S6.5主震震源体下方中下地壳存在大范围低速异常分布,P波速度异常扰动与重磁异常的展布特征、梯度变化在深度和分区特征上均具有较好的联系和可比性,结合昭通、莲峰断裂带中下地壳范围内存在大范围的低密度弱磁性异常分布,综合表明了该区中下地壳物质相对较为软弱,这种特有的深部物性结构特征有利于应力在脆性的上地壳�The 2014 Ludian M S6.5 earthquake occurred in the Zhaotong and Lianfeng fault zones on the southeastern margin of the Daliangshan secondary block in the eastward-protruding transitional deformation zone of the Chuandian diamond block,part of the north-south seismic belt in the southeastern margin of the Tibetan plateau.Over the past ten years,moderate-sized earthquakes on this fault zone and its surrounding areas have increased notably.Whether the deep structure of this fault zone can generate major earthquakes is an urgent issue to be addressed.This work attempted to answer this question and examines the deep dynamic mechanism of the 2014 Ludian M S6.5 earthquake.We collected data from seismic stations of the regional digital seismic networks of Yunnan and Sichuan and mobile seismic arrays of“Chinese seismic array detection-the southern section of North-South seismic belt(“Himalaya”project phase 1).Then we imaged the three-dimensional velocity structure beneath the Sichuan-Yunnan area using joint inversion of regional and teleseismic data.On this basis,the P-wave velocity structure of the Lianfeng and Zhaotong fault zones was studied exhaustively.And then we performed inversion gravity and aeromagnetic data to obtain apparent density,apparent magnetization intensity in the study area,which permits to reveal the deep dynamic environment of earthquakes.The results show that there are significant lateral medium differences in the upper crust of beneath the Zhaotong and Lianfeng fault zones and adjacent areas.The low velocity anomalies are present in the middle-lower c rust below the southwestern edge of the Daliang Shan secondary block,showing a nearly NS trend.The 2014 M S6.5 earthquake is located near the boundary between the high and low velocity anomalies and slightly tend toward the side of the high-velocity body.The P-wave velocity structure also reveals a large-scale low velocity anomaly distribution in the middle-lower crust below the M S6.5 mainshock source.The distribution of P-wave velocity perturb

关 键 词：昭通、莲峰断裂带 鲁甸M S6.5地震 速度结构 视密度、视磁化强度反演 

分 类 号：P315[天文地球—地震学]