2015-04-15阿拉善左旗5.8级地震前后构造应力场研究

Research on the Tectonic Stress Field before and after the April 15,2015 Alxa Left Banner MS5.8 Earthquake

采用振幅比方法计算2000~2018年鄂尔多斯块体西北缘M L2.5~5.0地震的震源机制解,对震源机制解各参数进行归一频度统计发现,应力轴的优势取向与该区构造应力场方向基本一致。利用自助线性反演方法,分3个时段分别反演巴彦浩特盆地和河套地震带的应力场方向,结果发现,2015-04-15阿拉善左旗5.8级地震前5 a巴彦浩特盆地应力场方向发生较大偏转,并与相邻的河套地震带的应力场方向形成一定角度的夹角,反演得到的主压应力场方向与本次地震的P轴方向一致,显示该地震受控于区域应力场;震后,巴彦浩特盆地主压应力场方向呈继承性发展,河套地震带的应力场受到影响,其主压应力场方向发生偏转,并与前者的应力场方向趋于一致。

In this paper,we use the amplitude ratio method to calculate the focal mechanism solution of the 2.5≤M L≤5.0 earthquakes in the northwest margin of the Ordos block,which occurred between the year of 2000 and 2018.Through the normalized frequency statistics of the parameters of focal mechanism solution,we find that the predominant orientation of stress axis is basically consistent with the tectonic stress field in this area.Using linear stress inversion bootstrap(LSIB)method,we retrieve the direction of stress field in Bayanhot basin and Hetao seismic belt in three periods.We find that 5 years before the April 15,2015 Alxa left banner M S5.8 earthquake,the direction of stress field in Bayanhot basin deflects largely,forming an angle with the Hetao seismic belt.The direction of principal compressive stress field of Bayanhot basin obtained by inversion is consistent with the P-axis direction of this earthquake,which shows that the M S5.8 earthquake is controlled by regional stress field.After the earthquake,the direction of principal compressive stress field in Bayanhot basin is inherited,the stress field of Hetao seismic belt is affected,and the direction of the principal compressive stress field deflects and is consistent with that of the former.