Seismogenic structure of Lushan earthquake and its relationship with Wenchuan earthquake

The Lushan earthquake occurred on the southern segment of the Longmenshan thrust belt between the Bayan Har and south China blocks.Field investigations indicated that there is no any earthquake surface rupture zone generated by this earthquake,only secondary surface breaks,such as extensional ground fissures,landslides,bedrock collapses,and liquefactions were found in the epicentral areas,which were caused by slope instability and earthquake vibration.The relocated aftershocks,focal mechanism solutions and surface structural geology further demonstrate that the seismogenic fault of the Lushan earthquake is a blind reverse fault which strikes 212° and dips toward NW with a dip angle of 38°±2°.The upper tip of this blind reverse fault is still at the depth of about 9 km in the upper crust.The structural deformation from above the tip to the ground surface is in accordance with a fault-propagation-anticline model.Besides,the differences in spatial aftershocks' distribution,rupturing process and seismogenic structure suggest that the Wenchuan and Lushan earthquakes are two independent rupturing events occurred along the middle segment and southern segment of the Longmenshan thrust belt,respectively.