重庆垫江M_S4.4地震:一个可能发生在浅地表的地震

Dianjiang,Chongqing,M_S4.4 earthquake:A possible shallow surface earthquake

为更好地认识2016年8月11日重庆垫江M_S4.4地震的发震成因,本文首先分析了近场地震台站记录到的该地震产生的短周期面波(Rg)强频散现象,该现象表明本次地震具有明显的浅震特征。然后采用CAP方法反演了该地震的震源机制解和震源深度,结果显示本次地震是走向为近EW向的逆冲型地震,矩震级为M_W4.1,最佳震源深度为1—2 km。在此基础上,结合现场震害、烈度等震线长轴方位和地质剖面图等资料,分析认为在区域应力集中加载作用下,震源区沉积盖层内部的软弱地层产生挤压变形,导致地层内斜交的裂隙发生切层失稳滑动,从而诱发了垫江M_S4.4地震,同时排除了震源区NE走向的黄钦垭口地表断层为发震构造的可能。

In order to better explore the causes of the M_S4.4 earthquake occurred on August 112016,in Dianjiang,Chongqing,this paper analyzes the strong dispersion of Rayleigh surface wave,and the phenomenon suggests that this earthquake has obvious shallow-source earthquake characteristics. Then,we obtained the focal mechanism and focal depth of the earthquake with CAP method. The results show that the earthquake is a thrust event with strike of nearly EW-trending,the moment magnitude is M_W4.1 and the estimated focal depth is 1-2 km.Finally,from the comprehensive research on mechanism solution,earthquake field damages,the isoseismal curve major axis direction and the geological section,we conclude that the Dianjiang M_S4.4 earthquake is caused by the slip of oblique fractures in the interlayers resulted from compressive deformations of soft strata in sedimentary covers under the concentrated loading of the regional stress field,excluding the possibility of the NE-trending Huangqinyakou fault as the seismogenic structure of the Dianjiang M_S4.4 earthquake.