松原前郭地震区孕震构造的地震层析成像研究

Seismic tomography of the Songyuan area,Northeast China:constraints on seismogenic structure

本文选取2013年10月到2018年12月期间松原市周边17个地震台记录到的515个地震事件的2926条P波和2665条S波到时数据,采用双差成像方法联合反演松原地震区震源参数和中上地壳(0~25 km)高分辨率三维体波速度和波速比结构,进而利用O′Connell-Budiansky理论估计了该区岩石介质的裂缝密度和饱和度参数.重定位后的震源参数精度有了显著提高.松原震区P波和S波的速度、波速比结构均表现出明显的不均匀特性,主要表现为低P波、低S波、低波速比结构,推测松原地震区发生更大地震的可能性较低.松原震群区浅地表区域(<5 km)整体表现为低P波、低S波和高波速比结构,而岩石介质的裂缝密度和饱和度表现为高值.浅层高波速比、高裂缝密度和高饱和度结构可能与流体有关;从区域构造出发表明松原地震发震构造与东北地区的区域构造应力场密切相关.松原震区的三维精细速度和高精度震源位置信息为深入了解该地区的地壳结构、孕震构造和地震活动性提供重要参考.

In this paper,we selected 2926 P-wave and 2665 S-wave arrival times of 515 seismic events recorded by 17 seismic stations around the Songyuan area,Northeast China from October 2013 to December 2018.We used the double-difference tomography method to determine the hypocentral parameters and the high-resolution 3D body wave velocity,velocity ratio(V_(P)/V_(S))structure of the middle and upper crust(0~20 km)beneath the Songyuan area,and then estimated the parameters of crack density and saturation rate of rock.The accuracy of the source parameters was improved significantly after relocation.The P-and S-wave velocity and V_(P)/V_(S)in this area show obvious non-uniformity,characterized by low P-wave,low S-wave velocity and low V_(P)/V_(S)beneath 5 km depth.Overall,the shallow crust(<5 km)has low P-wave and low S-wave velocity,high V_(P)/V_(S)ratio,and big anomalies of crack density and saturation degree,which may be related to fluids in the crust.In view of the regional tectonics,the seismogenic structure of the Songyuan area is closely related to the regional tectonic stress field in Northeast China.The high-resolution three-dimensional velocity structure and high precision hypocentral location of the Songyuan area presented in this paper provide an important reference for the further understanding of the crustal structure,seismogenic structure and earthquake activity in this region.