邢台地震前地壳形变异常的可能性物理机制

A POSSIBLE MECHANISM OF CRUSTAL DEFORMATION BEFORE LARGE EARTHQUAKE OF XINGTAI IN 1966

将地壳介质视为麦克斯威尔体 ,运用差分法和三维有限元方法 ,探讨了邢台分层地壳结构模型 (含高速体和低速体及深大断裂 )中深部断裂加速蠕滑时 ,平均应力、水平最大剪应力和地表面垂直位移随时间演化的特征 ,计算结果表明 :(1 )在地壳中上部 1 1km处 ,深部断裂的加速蠕滑急剧加速了水平最大剪应力的增加速率 ,可达数百倍 ,深部断裂的加速蠕滑是邢台强地震成核过程的开始 ,可实现地壳下部的能量向地壳中上部快速转移 ;(2 )深部断裂的加速蠕滑引起的地面垂直位移变化与邢台地震震前的地表面垂直位移变化非常一致 .说明邢台地震震前地壳表面垂直方向的位移不仅与岩石的膨胀有关 ,而且可能与地壳内深部断裂的加速蠕滑密切相关 .

Medium of the Crust is treated as maxwell medium, and the model includes hard and soft inclusion, as well as deep level faults. By using three dimensional finite element method and differential method. The time changes of the average disturbed stress and maximum disturbed shear stress and the crustal deformation on the surface of the model are calculated. The results show that (1) At 11km depth in the crust the change of maximum disturbed shear stress caused by the faster creep of the deep level fault is accelerated for hundreds of times. The beginning of the fault instability is the beginning of forming the “core” of Xingtai large earthquake in 1966. This character is very favorable to faster transferring of shear strain energy from the lower crust to the upper and middle crust. (2) The character of deformation on the model surface is very similar to that in Xingtai area before large earthquake in 1966. We can conclude that the precursor is connected not only with the dilatation of rock but also with the creep instability along the deep level fault before large earthquake. [