The M7.0 Lushan earthquake and the relationship with the M8.0 Wenchuan earthquake in Sichuan,China

On 20 April 2013 an M7.0 Lushan earthquake in the Sichuan of China occurred on the southern segment of the Longmenshan fault.According to the data of the telemeter seismographic network in Sichuan and the current correlative information from internal and overseas,we analyze the basic earthquake parameters,aftershock distribution,sequence attenuation characteristics.Our results show that the focal mechanisms of the Lushan earthquake result from a pure thrust and are consistent with the characteristics of Longmenshan fault structure.The Lushan earthquake is rich in aftershocks.More than 7800 aftershocks are logged since main-quake from 20 April to 5 May,2013.4 aftershocks of magnitude 5 or greater have occurred in the region.The largest aftershock is the M5.4 earthquake on April 21 at 17∶05 of Beijing time between Lushan and Qionglai counties.The long axis of aftershocks distribution ellipsoid is consistent with the Longmenshan fault structural trend.The lengths of the long and short axis of the aftershocks distribution ellipsoid are about 40 km and 20 km respectively.This indicates that the rupture scale of this earthquake is limited.From following aspects such as the focal mechanisms,the rupture process,aftershocks spatial distribution and the surface rupture,we compare the Lushan earthquake with the M8.0 Wenchuan earthquake and find that these two earthquakes are significantly different.The distance between the Lushan earthquake and the Wenchuan earthquake is about 90 km.The distance between two locations of the aftershock-intensive areas is 50 km.The Wenchuan earthquake made the middle-northern segment of the Longmenshan fault to rupture fully.The original location of the Lushan earthquake is in the southern segment of the Longmenshan fault.The rupture scale of the M7.0 event is limited.Although they are connected with each other on same seismogenic structure,they are two relatively independent seismic events.