2013年松原5级震群序列精定位、震源机制解及发震构造特征

Relocation and Focal Mechanism of the Songyuan Earthquake Swarm Sequence in 2013

东北松辽盆地内2013年10月、11月接连发生5次5级以上强震,该震群对研究东北地区孕震环境具有重要意义。本文采用双差定位算法和CAP方法(Cut and Paste)对松原5级震群序列的发震构造特征进行了详细研究。双差定位结果显示,松原5级震群序列震中分布长轴呈NW—SE向(长轴方位约317°),长度约10km,宽度约5km,与长岭—大山子断裂方位近乎垂直,震源深度主要集中在4～13km。19个M_S≥3.5地震的震源机制解结果显示,松原5级地震震群主要以逆冲、逆冲兼走滑型地震为主,震源机制节面解Ⅰ的优势方位为NW—SE向。综合分析小震精定位与中强地震震源机制解结果,我们认为,2013年松原5级震群序列的发震构造是一条与长岭—大山子断裂几乎垂直的隐伏断裂,震群序列中较大地震的初始破裂深度比质心深度深。松辽5级震源区的背景应力场既受太平洋板块对北东亚板块推挤作用的影响,又受松辽盆地内部断裂带的控制,在东北地区地下俯冲带深部强震活动的影响下,深震活动强化了地幔物质的扰动,进一步促进浅层介质的应力积累,松辽盆地内部断裂带交汇处相对薄弱,当应力积累到一定程度,便发生中强地震。

Double difference location algorithm and the CAP method （Cut and Paste） were used for the precision mapping and inversion of the focal mechanism solution for the Songyuan earthquake swarm above M5 in 2013. The double-difference location results show that the epicenter distribution sequence of the Songyuan M5 earthquake swarm is NW-SE, with a length of about 10 km, width of about 5 km, and a major axis of about 317°. It is almost perpendicular to the Changling-Dashanzi fault, and the focal depth is mainly concentrated at 2～14 km. The results of the focal mechanism solution of 19 Ms≥ 3.5 earthquakes indicate that the Songyuan M5 earthquake swarm is dominated by thrust, thrust and strike-slip earthquakes, and the dominant orientation of the focal plane solution I is NW-SE orientation. The depth of 19 earthquakes are focused on 4～6 km. The orientation of the epicentral distribution after the fine orientation is consistent with the dominant orientation of the focal mechanism solution plane Ⅰ. The seismogenic structure of the Songyuan M5 swarm is an invisible fault that is almost perpendicular to the Changling-- Dashanzi fault. The background stress field in the source area is affected not only by the push of the Pacific plate to the North East Asia plate, but also by the internal secondary fault zone of the Songliao basin, under the influence of deep seismic activity in the underground subduction zone of the Northeast China. The deep seismic activity has strength ened the disturbance of mantle material and further promoted the accumulation of stress in shallow medium. The junction of the secondary fault zone in Songliao basin is relatively weak, and when the stress accumulates to a certain extent, a moderate strong earthquake will occur.