四川芦山Mw 6.6级地震发震构造

摘要

2013年4月20日四川芦山Mw6.6级地震发生在龙门山构造带南段,未见典型的同震地表破裂.作者在对震后400余个地震破坏宏观调查点重新厘定的基础上,参考四川数字强震台网的近场峰值加速度(PGA)记录,绘制的本次地震等震线图的极震区地震烈度为Ⅸ度,略呈长轴为NE向的扁椭圆状,不具明显的方向性.进一步综合3 323个早期余震重新定位结果、石油地震勘探剖面和震源机制解等,判定本次地震的主要发震构造为控制蒙山东麓的大邑断裂,系龙门山构造带南段NW-SE向缩短所导致的大邑断裂上冲作用的结果;新开店断裂亦在深部产生了同震破裂,造成了断裂上盘震害明显高于下盘的断层上盘效应现象.%On April 20,2013,the Lushan Mw 6.6 earthquake occurred on the south segment of the Longmenshan fault zone and no significant coseismic ground rupture was observed.In this paper,the authors define the distribution of the intensity of this earthquake after redefining more than 400 macro-seismic damage survey points and referring to the near field ground acceleration (PGA) record of the Sichuan digital strong motion seismic network.The intensity of epicenter region reached Ⅸ degree on Chinese seismic intensity scale,slightly showing flat oval shape with the long axis to NE,without apparent direction.Furthermore,after consolidating the results of relocating 3 323 early aftershocks,petroleum seismic exploration profiles and focal mechanism solutions,the authors think that the Dayi fault controlling the east piedmont of Mengshan is the main causative structure of the Lushan earthquake,resulting from the thrusting of the Dayi fault induced by shortening of the Longmenshan fault zone in NW-SE direction.The Xinkaidian fault also produces coseismic ruptures in the depth,causing the phenomena that the earthquake damage on the hanging wall is significantly higher than that on the footwall.