唐山地区主要断裂应力状态

Stress State of Main Faults in Tangshan Area

利用唐山地区断层位置、速度结构和292个震源机制解数据,对断裂段进行应力场反演空间网格划分,采用网格搜索法反演唐山地区整体及主要断裂应力场。研究发现:1)2011年日本东北M_W9.0地震发生前后,唐山地区整体区域构造应力场发生较小的顺时针旋转,且由走滑型应力状态变为正走滑型应力状态,该变化可能主要由震源机制解空间位置变化引起。2)日本东北地震使唐山部分地区σ_(1)轴倾伏角由陡倾斜变为水平,且应力场发生较小的顺时针旋转。3)当前唐山地区整体区域应力场特征为σ_(1)轴NEE-SWW向,σ_(3)轴近NS向,R值为0,与前人研究结果一致。表明唐山地区应力场已调整至1976年唐山M_W7.8地震前的状态,且应力状态偏张性性质。4)当前巍山-丰南、陡河、滦县-乐亭断裂段6~20 km、陡河断裂段11~20 km为走滑型应力状态;陡河断裂段0~10 km为正走滑型应力状态;雷庄、陈官屯和卢龙断裂段6~20 km、巍山-丰南断裂段0~5 km为正断型应力状态。以上断裂σ_(1)轴方向与该区域主应变方向和剪切波分裂的快波偏振方向等结果一致。5)唐山地区整体处于一个相对统一的NNW-SSE向的拉张作用控制,但古冶、滦县地区处于NEE-SWW向的挤压作用控制。

Based on the data of fault location,velocity structure and 292 focal mechanisms in Tangshan area,we carry out the spatial grid division of stress field inversion,and retrieve the whole and major fault stress fields in Tangshan area by using grid search method.The results show that:1)Before and after the 2011 M W9.0 Tohoku earthquake,the overall regional tectonic stress field in Tangshan area rotated slightly clockwise,and the stress state changed from strike-slip to positive strike-slip,which may be mainly caused by the spatial location change of the focal mechanism solution.2)The Tohoku earthquake in Japan made the plunge angle ofσ_(1)-axis in some areas of Tangshan change from steep to horizontal,and the stress field has a small clockwise rotation.3)At present,the overall regional stress field in Tangshan area is characterized byσ_(1)-axis NEE-SWW direction,σ_(3)-axis near NS direction,and R value is 0,which is consistent with previous research results.It shows that the stress field in Tangshan area has been adjusted to the state before the 1976 Tangshan M W7.8 earthquake,and the stress state is partial tensile.4)At present,6-20 km of Weishan-Fengnan,Douhe,Luanxian-Leting fault sections and 11-20 km of Douhe fault section are strike-slip stress states;The stress state of 0-10 km of Douhe fault section is positive strike-slip.6-20 km of Leizhuang,Chenguantun and Lulong fault segments,0-5 km of Weishan-Fengnan fault segments are positive fault type stress states.Theσ_(1)-axis directions of the above faults are consistent with the principal strain direction and the fast wave polarization direction of shear wave splitting in this region.5)The Tangshan area is in a relatively unified NNW-SSE tensile action,but the Guye and Luanxian areas are in NEE-SWW compressive action.