1976年唐山M_S7.8地震同震及现今形变特征

Coseismic and contemporary deformation features of the M_S7.8 Tangshan earthquake in 1976

基于1976年唐山M_S7.8地震的同震位移和现今GPS速度结果,本文分析了该地震的同震破裂参数、同震应变释放分布及其现今应变积累特征.对唐山同震位移二维位错解析公式的拟合结果显示,唐山地震前的断层闭锁深度约为18—23km,断层倾角可能介于74°—90°之间,同震位错量约为3.1—3.4m.在同震过程中沿发震断层表现出显著的右旋错动特征,在发震断层两侧沿NE向表现出左旋应变释放特征.在本文现有的GPS测站密度和精度情况下,尚无法识别出现今阶段沿唐山断裂的明显蠕滑特征.唐山同震应变释放和现今GPS应变率积累结果均显示,唐山断裂SE侧的剪切形变(速率)量值大于其NW侧,同震与现今阶段的形变量值相差约1 000倍.

This paper analyzed the coseismic rupture parameters,distribution of coseismic strain release and contemporary strain accumulation features based on coseismic displacements and GPS velocities in source area of the M_S7.8 Tangshan earthquake in 1976.The fitting results for the dislocation formula in twodimensional model of coseismic displacements show that the locking depth of seismic fault is about 18—23km before Tangshan earthquake,its dip angle is about 74°—90°,and the coseismic dislocation is about 3.1—3.4m.During the coseismic process,right-lateral rupture occurred in the Tangshan fault zone,and the left-lateral strain released in NE direction at the bilateral sides of the coseismic fault.On the condition of the density and accuracy of GPS surveying presented in this paper,the creep signal cannot be distinguished at present.The coseismic strain release and contemporary GPS strain rate accumulation results illustrate that the shearing deformation（rate）magnitude in the SE side of the Tangshan fault zone is larger than that in the NW side,and the deformation values between the coseismic process and contemporary period differs 1 000 times.