基于发震断裂位移的汶川地震区地应力场突变特征反演分析

BACK ANALYSIS ON MUTATION CHARACTERISTICS OF REGIONAL GEOSTRESS BASED ON SEISMOGENIC FAULT DISPLACEMENT OF WENCHUAN EARTHQUAKE

本文采用数值反演分析方法，综合考虑发震断裂位移、地应力实测和区域GPS位移3种基本特征参数，获得了龙门山地区汶川地震前后地应力的突变特征与变化规律。研究表明，汶川地震前龙门山地区构造应力的平均量值为12.6～12.8MPa，最大主应力的方向为NW-NEE向。汶川地震导致龙门山地区的地应力发生复杂变化，具有突变效应、上下盘效应和距离效应。震后发震断层上盘的构造应力平均值为11.30MPa，下盘构造应力的平均值为6.50MPa，最大主应力的方向变化为NWW到NEE向。地震后以发震断裂为界的地应力有明显的突变特征，表现为应力不同程度的释放或局部增高，尤其是下盘地应力释放明显，而上盘既有地应力的释放区也有局部地应力增高区，随着距发震断裂距离的增大，地应力的突变效应逐渐减弱。

Based on the dislocations of earthquake faults, the geostress measurement and GPS regional displacements, this paper aims to explore the variation of geostress in the Longmenshan mountainous area before and after the 2008 Wenchuan earthquake using numerical inversion analysis method. The results of numerical simulation demonstrate that the average tectonic goestress in the Longmenshan mountainous area ranged from 12.6 MPa to 12.8 MPa before the Wenchuan earthquake. The direction of maximum principal stress ranges from NW to NEE.An clear change of geostress had been caused by the Wenchuan earthquake. It behaves mutation effect, hanging wall and footwall effect, and distance effect. The tectonic geostress of the hanging wall of the earthquake faults reached an average of 11.30MPa, whereas the geostress of the footwall at an average of 6.50 MPa. Meanwhile, the direction of maximum principal stress ranged from NWW to NEE.The geostress had clear mutation characteristics, which appeared to be the release or local increase of the geostress. Especially the geostress was released obviously at the foot wall. Different degree of geostress releases or locally rises at the hanging wall. With the increase of distance to the earthquake faults, the mutation effect of the geostress was gradually weakened.