2019年6月17日四川长宁地震重定位及震源机制研究

Relocation and focal mechanism inversion for the Changning,Sichuan,earthquake on 7 June 2019

采用双差重定位和W震相波形反演方法分析"地震编目系统"和中国地震台网中心提供的地震观测报告及区域地震波形数据,对2019年四川长宁地震序列进行了重定位,反演获取了M>4.5地震的震源机制解。地震序列重定位结果显示,长宁地震序列沿NW优势方向呈条带状分布,集中分布于5-10 km深度范围,且发震断层面呈高倾角。震源机制反演结果表明,2019年6月17日四川长宁M_S6.0主震的两个可能发震断层面参数分别为:节面Ⅰ走向12°,倾角50°,滑动角139°;节面Ⅱ走向131°,倾角59°,滑动角48°,最优矩心深度为7.5 km,矩震级M_W5.74。此外几个M>4.5余震的震源机制也基本与主震类似,均为以逆断为主外加少量走滑的地震破裂事件。综合分析长宁地震序列的重定位、震源机制反演结果以及震中和附近区域的地质构造背景信息推断,本次长宁主震的发震破裂面呈NW-SE走向,发震断层为长宁-双河背斜东北翼发育的逆冲断层。

In this study,we apply the double-difference relocation technique and W-phase method to relocate the 2019 Changning,Sichuan,earthquake sequence,and to determine the focal mechanisms of the M>4.5 aftershocks using the seismic data provided by the Earthquake Catalog System and China Earthquake Networks Center. The relocated epicentral locations of Changning earthquake sequence show a NW-striking dominant narrow belt in the predominant epicentral depth range of 5-10 km with a near vertical seismogenic fault plane. The focal parameters for the main shock of 17 June,2019 Sichuan Changning earthquake are:strike 12°,dip50°,strike 139° for the nodal plane Ⅰ,and strike 131°,dip 59°,strike 48° for the nodal planeⅡ,focal depth is 7.5 km and moment magnitude is M_W5.74. Moreover,the M>4.5 aftershocks show a similar focal mechanism to the main shock. Combined analyses of the relocated epicentral location,focal mechanisms and tectonic settings suggest that the seismogenic fault of 17 June 2019 Changning main shock could be related to the thrust fault developed in north-eastern wing of NW-SE-striking Changning-Shuanhe anticline.