地震破裂过程的研究

研究震源力学模型的一个新方向是用动态扩展的剪切裂纹模拟地震破裂过程。本文利用裂端有塑性区薄层且断层面上有摩擦力的平面剪切裂纹错动模式来表示地震破裂过程,对运动方程和边界条件进行拉氏变换和傅氏变换,利用维纳-霍普（Wiener-Hopf）方法和卡格尼阿（Cagniard）方法得到了断层面上的位移和应力表达式。根据裂端附近的能量平衡条件,计算了地震破裂的平均速度和塑性区尺度,还讨论了断层面上的位错分布函数,并对某些前震地震波高频成分增多的现象提出了解释。在本文假定的参数条件下,地震破裂的平均速度c=0.72β,β是介质的剪切波速。塑性区尺度约为地震新断层总长度（包括塑性区）的12％。按本文的结果,由于破裂速度的增加,前震的震波初动半周期减小的异常幅度不会超过39％。

A STUDY OF THE EARTHQUAKE FAULTING PROCESS

A recent trend in research of the mechanical modeling of an earthquake source is to look upon the source as a dynamically extending shear crack. In this paper, the authors have proposed a plane shear faulting model to simulate the rupture pro-cess of faulting during an earthquake. In this model, the friction force on the fault plane and the plastic region near the fault tip are considerd. By applying the Wiener-Hopf technique and the Cagniard-de Hoop method, the expressions for the displacement and stress are obtained. With the help of the energy balance condi-tion in the small region around the fault tip, the average velocity C of the earthquake faulting and the scale of the plastic region are calculated. The dislocation distribu-tion function on the fault is discussed and the phenomenon that the high frequency components of certain foreshocks increase before great shocks is also explained. Here, according to the assumed conditions and parameters, the average velocity of the ear-thquake faulting c = 0.72 β, where β is the velocity of the S-wave, the scale of the plastic region is about 12% of the total length of the new fault. As to the seismie wave of such foreshocks, the decrease of half period of the first P arrivals due to the increase of rupture velocity will not exceed 39%.