鄂尔多斯块体周缘地区近期地震活动性与汶川地震应力触发作用的关系

Investigation on the possible triggered seismicity in the peripheral areas of the Ordos block by the Wenchuan earthquake.

采用β统计对汶川地震前后鄂尔多斯块体周缘地区的地震活动率进行了空间扫描分析,并采用JiChen的震源破裂模型计算了汶川地震产生的库仑破裂应力变化,以研究鄂尔多斯块体周缘地区近期地震活动性与汶川地震应力触发作用的关系。结果发现,鄂尔多斯块体西南缘弧形断裂束的南东段与南缘渭河盆地的地震活动率在汶川地震后提高显著,其他区域的地震活动率没有明显提高,库仑破裂应力计算得到两个区域的应力变化范围分别为0.005～0.02 MPa和0.001～0.01 MPa,表明汶川地震有可能触发了这两个区域的地震活动。鄂尔多斯块体东缘的山西断陷带处于库仑破裂应力计算的应力增加区,应力变化范围为0～0.012 MPa,2009年3月以来发生的4次ML4.5～5.2级强有感至微破坏地震有可能被汶川地震所延迟触发。b值、地震能量释放率与空间相关距离SCL等地震活动性参数随时间变化扫描结果显示,该区域可能处于不断趋近高应力累积的状态,其未来大震有可能提前发生。西缘地区为应力减小区,其目前的地震活动处于正常水平状态。

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.