走滑型地震前断面位错加速运动和一种可能的短期前兆机制

本文初步讨论了半无限分层弹性空间中离散螺型位错群不均匀运动过程的二维问题,以及岩石层中浅源走滑型地震的孕育过程。研究表明,在区域构造应力和象力作用下,岩石层中部断面上高摩擦阻抗闭锁被克服之后,断面位错将逐渐加速运动,在花岗岩层上界面附近,位错速度接近横波速度（等价于发生地震）;该运动过程的持续时间约为几天至几个月;当岩石层中、上部的物质常数n=3和闭锁深度η₁=60km时,期望在大地震之前位错加速运动的持续时间内,观测到总应变量为10^-7.所以,上述过程可能是大地震前短期前兆异常变化的机制之一。

ACCELERATED MOTION OF DISLOCATIONS OF THE FAULT BEFORE A STRIKE-SLIP EARTHQUAKE AND A POSSIBLE MECHANISM OF SHORT-TERM PRECURSORS

In this paper, a two-dimensional problem about the non-uniform motion of dis-crete screw dislocation group in the eiastic and layered half space was discussed, and theresults are applied to describe the preparation process of great shallow strike-slip earth-quake. It is shown that when the high friction on the locked fault in the middle partof the lithosphere was overcome under regional tectonic stress and image force, disloca-tions on the fault begin to move, and are accelerated gradully, and its velocity reachesthat of shear waves finally at the upper boundary surface of the granitic layer. In ac-cordance with our calculation, the duration of the process of accelerating dislocationmotion is about a few days to a few months, the total strain on the surface might reachto 10^-7 during the time before a great earthquake if the material constant is n=3 in theupper and middle parts of the lithosphere and the locked depth is η₁=60 km. It is ourpreliminary conclusion that the above process might be a possible mechanism of short-term precusory changes prior to a great shock.