Abstract In order to understand the feature of seismic activity before Wenchuan earthquake in the source initial rupture area，the regional seismic source location of two larger earthquakes in Dujiangyan prior to Wenchuan earthquake was determined again，and the focal mechanism solution of the earthquakes was calculated.The result shows:1）Before M8.0 earthquake，seismic activity in the source initial rupture area increased and formed a belt.The southeast end of the belt locates Dujiangyan Juyuan Town，then spreads in about 42 angle direction toword westnorth direction and ends at Dujiangyan Longxi Town，with a length of 20 km.2）The focal depth of the earthquakes in the southeast region is relatively shallow with a depth of 10 km.，In the time series,，the seismic activity extended from southeast to northwest，passed Zipingpu reservoir area and ended in the initial rupture area of Wenchuang earthquake where focal depth is about 7 km；deeper than that in the southeast region.3）The sliding angle of focal mechanism solution of the ML3.7 earthquake on February 14 is 93 degree，the NE wall moved vertically downward which is consistant with focal mechanism solution of the earthquakes near the initial rupture point of the Wenchuan earthquake.That means that the initial rupture point of the Wenchuan earthquake had been torn before the earthquake，and the necessary condition of Wenchuang earthquake had been ready.4）The ML3.8 earthquake on February 28 located in the Longmenshan central faults，and the focal mechanism solution is consistent with Wenchuan earthquake.It，belongs to the direct foreshock.
Wei Yaling,Cai Yichuan,Su Jinrong. THE PRECURSORY IMAGE OF SMALL EARTHQUAKE SWARM
TEAR TOWARD THE INITIAL RUPTURE POINT OF THE
WENCHUAN PRINCIPAL EARTHQUAKE[J]. jgg, 2014, 34(5): 17-20.
Wei Yaling,Cai Yichuan,Su Jinrong. THE PRECURSORY IMAGE OF SMALL EARTHQUAKE SWARM
TEAR TOWARD THE INITIAL RUPTURE POINT OF THE
WENCHUAN PRINCIPAL EARTHQUAKE[J]. jgg, 2014, 34(5): 17-20.
