Relocation of the Lushan Ms7. 0 earthquake sequence and its tectonic implication

Using travel time data from the Sichuan Seismic Network and the double difference relocation algorithm, we determined accurate locations of the Lushan M(s)7. 0 earthquake and aftershocks. The aim is to determine seismogenic faults and to place constraints on geometry of the fault plane according to the aftershock distribution, and also to analyze aftershock activities. The results indicate that the epicenter of the Lushan M(s)7. 0 main shock is located at 30. 28 degrees N, 102. 99 degrees E and its focal depth is 16. 33 km. The aftershocks are distributed within a region 32 km long and 15 similar to 20 km wide, with depths ranging 5 similar to 24 km. The seismic rupture extends relatively longer to the southwest of the main shock epicenter than that to the northeast. Magnitudes of the aftershocks decrease rapidly with time. Focal depth distributions show a clear thrust rupture within the crust, which is a hidden fault about 10 km east of the Dachuan-Shuangshi fault zone. We estimate that the fault plane has a strike of 217 degrees and dips to the northwest at 45 degrees angle, almost parallel to the Dachuan-Shuangshi fault zone only with a gentle dipping angle. Both of them belong to the imbricate thrust system of the Longmengshan range-front fault zone. Affected by this fault, the aftershocks also occurred on the Dachuan-Shuangshil fault zone, parts of which extend to the southwestern margin of the Baoxing massif in the northwest. From Baoxing massif zone to the southern end of the Wenchuan M(s)8. 0 earthquake rupture zone is a 50 km long seismic gap, which is considered to have a potential risk of a large earthquake in the future.