唐山、汶川地震地壳形变特征综合研究

Characteristic of crustal deformation related to Tangshan and Wenchuan eathquakes

通过对比分析1976年唐山7.8级和2008年汶川8.0级地震前后的区域水平和垂直形变场及跨断层形变的时空特征,归纳总结了与大地震孕育物理过程相关联的地壳形变共性特征.主要认识如下:(1)在中国大陆复杂的构造孕震环境下区域地壳形变场充分表现出非稳定态的起伏消长和复杂变化,在强震前孕震区地壳形变经历先增强后弱化的动态特征,剧烈形变局部化可能出现在震源区边缘附近;(2)震源区在震前数年主要表现为弱变形状态,可能是孕震晚期发震断层强闭锁、断层近场应力应变积累趋于极限的表现;(3)两次大地震前发震断层区域形变均显著偏离长期构造应变积累的变形方式,反映在大陆内部小尺度多块体的复杂构造孕震环境下局部应力应变场更容易出现扰动,且小块体边界临近发震的断层响应更为显著;(4)震源区边缘或外围可能出现显著的断层形变异常,而震源区内部由于发震断层处于强闭锁状态而不易观测到断层形变异常.

The identical characteristics of crustal deformation related to geophysical pregnant process of big earthquakes are summarized by comparing the regional horizontal and vertical crustal deformation and fault deformation pre and post Tangshan earthquake occurred in 1976 with that of Wenchuan earthquake occurred in 2008. The main achievements obtained in this paper are as follows：（1） Under the complex tectonic seismic pregnant environment of China mainland the regional crustal deformation behaves non-stable rising and falling with complex variation. Before strong earthquakes the crustal deformation in the seismogenic region experiences dynamic variation from strengthen to weaken with the localization of strong deformation appears in edge of the seismogenic region.（2）The weaken deformation state in the seismogenic region before years of earthquakes may be caused by the strong locked state of causative fault and the stress and strain accumulation tending to limitation in near-field during the later period of earthquake preparation.（3）The deformation in the area of causative fault before this two big earthquakes noticeably deviate from the tectonic strain accumulation mode in long term,which reflect the easily perturbation of stress and strain field under the complex tectonic seismic pregnant environment in China mainland with multi small blocks,and the more significant response in the edge of small blocks nearing the causative fault.（4） Anomalous fault deformation may appear in marginal and peripheral regions of seismogenic region,but it is not easily observed inner the seismogenic region as the causative fault is strongly locked.