Determination of the rupture fault by Lushan 7.0 Earthquake from accurate location of aftershocks

Lushan earthquake with magnitude 7.0 occurred in the south section of the Longmenshan Fault Zone on 20 April 2103. At the source region, there are several faults which are the Dayi-minshan Fault, the Shuangshi-dachuan Fault, the Yanjing-wulong Fault and the Genda-longdong Fault, and there are also several editions of the fault structure map of this area. From the field investigation, no obvious surface split in earthquake area is found but some small sites of spurting water and sand along NW extension fractures. So which fault causes the Lushan Earthquake? It causes the wide discusses in China. After Lushan 7.0 Earthquake, 15 mobile seismic stations were set around the source region. During 20 April 2013 to 28 April 2013, 4481 aftershocks were observed and 3381 aftershocks were recorded by 4 stations at least. We relocated the 3381 aftershocks using double-difference location method, and obtained the hypocenters of 3328 aftershocks. The hypocenters indicate that the earthquake fault has the dip of 40-45°and strike of 30-35°, and the distribution of some aftershocks is perpendicular to the fault surface, which explains the appearance of spurting water and sand along NW fractures. Because that the main depth of aftershocks is about 7-22km and the largest slip of the main shock is 1.5m according to the estimate of fracture process, there is no obvious surface split in earthquake area. We extend the fault line at the vertical section of hypocenters' distribution, and the result shows the fracture fault ( thrust fault ) should be the Dayi-minshan Fault and we prefer the Zhang Peizhen's fault structure map.