The spatial distribution pattern of landslides triggered by the 20 April 2013 Lushan earthquake of China and its implication to identification of the seismogenic fault

After the 20 April 2013 Lushan M (S) 6.6 earthquake occurred, investigation and identification of the seismogenic fault for this event have become a focused and debatable issue. This work prepared an initial landslide inventory map related to the Lushan earthquake based on field investigations and visual interpretation of high-resolution aerial photographs and provided evidence for solving the issue aforementioned. The analysis of three landslide-density profiles perpendicular to strike direction of the probable seismogenic fault shows that many landslides occurred on the footwall of the Shuangshi-Dachuan fault (SDF), without sudden change of landslide density near the fault. Very few landslides were detected near the Dayi fault (DF) and also no change of landslide density there. While obvious sudden change of landslide density appeared about 1-2 km from the northwest to the western Shangli fault (WSF), and the landslide density on the hanging wall of the fault is obviously higher than that of on the footwall. Therefore, we infer that the seismogenic fault for the Lushan earthquake is neither the SDF nor the DF, rather probably the WSF located between these two faults, which is an evident linear trace on the earth surface. Meanwhile, the coseismic slip did not propagate upward to the ground, implying the Lushan earthquake was spawned by a blind-thrust-fault beneath the WSF.