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2013年4月20日的芦山“4·20”M S7.0地震发生在龙门山断裂带西南段,震中地区分布多条NE向断裂,构造较为复杂。这次地震震源机制解显示为逆冲型地震,破裂面为NE走向,与龙门山断裂带的运动性质和走向一致。地表调查只在大川-双石断裂(前山断裂)和新开店断裂(大邑断裂南段)发现局部分布的NE向地表裂缝、沿地表裂缝分布的喷砂冒水和砂土液化,不规则的边坡开裂等地表变形,以及断裂沿线较严重的滑坡崩塌和房屋破坏。野外调查没有发现明显的地震地表破裂。GPS测量结果显示,此次地震的发震断裂位于芦山县城附近或其以东,而芦山西侧的断裂也可能参与了部分活动。根据野外地质调查、GPS观测、震源机制解、震源深度、余震分布等结果综合判定,芦山7.0级地震的主要发震构造是芦山之下、大川-双石断裂和新开店断裂之间的龙门山前缘滑脱带。此滑脱带在该段的运动导致了这次地震的发生,并可能带动了它上面的大川-双石和新开店等断裂的活动。
The Lushan “4.20 ” M S7.0 earthquake on April 20, 2013 occurred in the southwestern segment of the Longmenshan fault zone, and several NE-trending faults were distributed in the epicenter area. The structure is rather complex. The focal mechanism solution of the earthquake is shown as a thrust type earthquake with the rupture plane being NE-trending, consistent with the nature and direction of the movement of the Longmen Shan fault zone. The surface survey only found NE-directed surface cracks in the Ochuan-Shuangshi fracture (Qianshan fault) and Xinjiandian fault (the southern section of Dayi fault), sandblasting and sand liquefaction along the surface crack distribution, and irregular edges Slope cracking and other surface deformation, as well as the more serious fracture along the landslide collapse and housing damage. No significant earthquake surface rupture was found in the field survey. GPS measurements show that the seismogenic fault of this earthquake is located near or to the east of Lushan County, and faults on the west side of Lushan may also be involved in some activities. Based on the results of field geological survey, GPS observation, focal mechanism solution, focal depth and aftershock distribution, the main seismogenic structure of the Lushan M 7.0 earthquake is under the Lushan Mountain, and the front of the Longmen Piedmont between the Okawa-Shimen fracture and the Xinjiandian fault Edge slip off. The movement of the slip-off belt in this section led to the earthquake and may have led to the rupture of the above activities, such as the Dachuan-Shishi and the newly opened shop.