唐山地区主要断裂应力状态OA北大核心CSTPCD

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 Mw9.0 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 of σ1-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 by σ1-axis NEE-SWW direction,σ3-axis near NS direc-tion,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 Mw7.8 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.The σ1-axis direc-tions of the above faults are consistent with the principal strain direction and the fast wave polarization direc-tion 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.