A brief talk on the 20 April 2013 Lushan M_W6.7 earthquake

An earthquake sequence is a retrospective designation of earthquake phenomena, and it can only be identified without doubt after the earthquake sequence has been completed. In view of the integrity, uniformity and systematicness of the Longmenshan fault zone or seismic belt, there is no denying the fact that the 20 April 2013 M_W6.7 Lushan earthquake which occurred in the southwestern segment of the Longmenshan fault is an event of the Longmenshan fault zone as the 12 May 2008 M_W7.9 Wenchuan earthquake. Taking into account the hypocentral location, focal mechanism, magnitude and ruptured area of the Lushan earthquake, it is preferable that the Lushan earthquake is the largest aftershock up to the present, of the 2008 M_W7.9 Wenchuan mainshock. Due to the fact that the identificaion of an earthquake sequencc is phenomenalogical description with arbitrariness to some extent, whether the Lushan earthquake is a new mainshock or one of the aftershocks of the 2008 Wenchuan earthquake is based on empirical knowledge and remains unsolved till the whole earthquake sequence has been completed, even though at present the arguments of the “one of the aftershocks of the Wenchuan earthquake” are convincing. It is emphasized that prompt solution should be given to some outstanding scientific issues related to the Lushan earthquake as well as prevention and mitigation of earthquake disasters.