首都圈地区跨断层形变观测与地壳应力场

CROSS-FAULT DEFORMATION OBSERVATION AND CRUSTAL STRESS FIELD IN CAPITAL CIRCLE REGION

通过首都圈地区11个跨断层测点的形变观测资料,将断层两盘作为不变形的刚体来分析断面相对滑动与地表两盘点位相对位移的定量关系,并以唐山地震及其余震为时间界限,将所得的断层滑动矢量分为2大时段,拟合区域2个不同时段的现今地壳上部应力状态,发现首都圈地区依据跨断层形变观测资料反演的地壳上部应力状态在唐山地震前后存在着较为明显的变化特征:1)第1时段(唐山地震及其余震期间),地壳应力状态以NNE-SSW向挤压,NWW-SEE向拉张为主要特征,反映该区构造应力场在NNE-SSW向的构造应力作用是逐渐增强的;在NWW-SEE向,其构造应力作用相对于NNE-SSW向有所减弱,表现为相对松弛状态。2)第2时段,在唐山地震及其余震之后的3个次级时段内,地壳上部应力状态以NNW-SSE向拉张为主要特征,表明在唐山地震及其余震之后,研究区的构造应力作用一直处于近SN向的松弛状态。

Based on the deformation observation data of 11 cross-fault survey points in the capital circle region and taking the two walls of fault as indeformable rigid block,we analyze the quantitative relation between the relative sliding of fault plane and relative displacement of the sites on the two walls on the ground surface,and then taking the Tangshan earthquake and its aftershocks as time-bound,we divide the fault slip complexor into two time-intervals, fit the regional stress state of the two different time-intervals in the upper crust and find that the stress state in the upper crust inverted by the data of crossfault deformation observation has changed obviously after the Tangshan earthquake. 1 ） In the first time interval（during Tangshan earthquake） , the crustal stress state was characterized by NNE-SSW compressional stress and NWW-SSE extensional stress; the tectonic stress action in NNE-SSW direction was gradually enhancing,while in NWW-SEE direction,it was weakening and characterized by stress relaxation. 2） In the second time interval,that is,in the 3 sub-time intervals after the Tangshan earthquake and its after-shocks,the upper crustal stress state was characterized by NNW-SSE extensional stress,indicating that in this time interval from the Tangshan earthquake and its after-shocks till now, the tectonic stress action of the region is all along in a relaxation state of NS direction.