Abstract:

In order to investigate the seismicity possibly triggered by the Wenchuan earthquake, we analyzed the spatiallyscanned variation of the seismicity rates in the  peripheral areas  of the Ordos block prior to and after the Wenchuan earthquake using  the β statistics, and calculated the Coulomb stress changes, using the rupture model of Ji (2008).  The result shows that the seismicity rate increased obviously both on the southeastern segment of the arcuate fault bundle on the southwestern border  and in the Weihe downfaulted basin zone on the south border of the Ordos block, which corresponds  to the calculated Coulomb stress change values of 0005002 MPa and 0001001 MPa respectively, suggesting that the seismicity of the two areas may have been triggered by the Wenchuan earthquake. The Shanxi downfaulted lenovo basin zone in the eastern margin of the Ordos block  is located  in the area of  increasing stress with the change value of 00012 MPa. Four felt earthquakes with magnitudes of ML 4552 have occurred there since the March of 2009,  which were possibly delay triggered  by the Wenchuan earthquake. The results from the temporal variation of the seismicity parameters of b value, from earthquake energy release rate and SCL show that this region  probably tends to accumulate high stress. The future large earthquake may occur in advance than expected. While the stress in the western margin  has been decreasing  since  the Wenchuan earthquake, and the  present seismicity level keeps in a normal state.

Key words:  seismicity, β-statistics, Wenchuan earthquake, stress trigger, peripheral areas of Ordos block