SOME THOUGHTS ON THE M_S 8.0 WENCHUAN,SICHUAN EARTHQUAKE

The MS 8.0 Wenchuan earthquake caused tremendous disaster to the country and people,and meanwhile it also gives us many lessons worth thinking about.The severe earthquake disaster tells us the necessity of evaluating and surveying the seismic and geological environment in urban and township construction so as to avoid the unfavorable terrain conditions and keep away from the instable sites prone to landslide,soil liquefaction and mud-rock flow and etc,complying stringently the standards for disaster fortification regulated by the state and the relevant technical code for seismic design of buildings,including the houses in rural area,and intensifying the study on active tectonics to avoid the active faults and possible seismogenic tectonics.Since the historical earthquake record is too short and the recurrence interval of earthquakes is long within the continent,we should be cautious when using the principle of recurrence of historical earthquake in seismic hazard assessment,but promote the study on paleoearthquakes on active tectonics,so as to fully understand the history of earthquake recurrence.Big earthquake may also occur on low-slip-rate active fault,but with longer recurrence interval.So special attention be paid to the elapsed time of the latest event on it.The source rupture of the MS 8.0 Wenchuan earthquake is characterized by a multi-point rupturing process,resulting from the expansion of deep fault from the detachment zone to the front-end ramp,and shown as double-ramp faulting on the surface.In the source rupture propagating process,the nature of the rupture changed.The southwest section is characterized with thrust faulting,and the northeast section turns to be dominated by strike-slipping.The initial thrust-type rupture occurring in the middle of the Longmenshan tectonic belt ran through its northeast section and became a new fault.The 1997 Mani,the 2001 west pass of Kunlun Mountains and the 2008 Wenchuan earthquakes with MS 7～8 are all the products of the movement of the Bayahar block.After the Wenchuan earthquake,a series of earthquakes with magnitude around 6 occurred in the Qinghai-Tibetan Fault block region,which characterizes the new episode of seismic activity of the Qinghai-Tibet Plateau block region.