The April 20,2013, Ms 7.0 Lushan earthquake occurred along the southwestern part of the Longmen Shan Fault zone. Tectonics around the epicenter area is complicated and several NE- trending faults are developed. Focal mechanisms of the main shock and inversions from finite fault model suggest that the earthquake occurred on a northeast-trending,moderately dipping reverse fault, which is consistent with the strike and slip of the Longmen Shan Fault zone. NE-trending ground fissures and soil liquefaction along the fissures, heavy landslides along the Dachuan-Shuangshi and Xinkaidian Faults were observed during the field investigations. No surface ruptures were found in the field work. GPS data indicate that the fault on which this earthquake occurred is a fault east of or near the Lushan county and the earthquake also triggered slip on the fault west of the Lushan county. Field observations, GPS data, focal fault plane,focal depth, and distribution of the aftershocks suggest, that the seismogenic structure associated with the Ms 7.0 Lushan earthquake is the d6collement beneath the folds of the eastern Longmen Shan. Slip along this decollement generated the earthquake, and also triggered the slip along the Dachuan-Shuangshi and Xinkaidian Faults.