鲜水河断裂带大震复发机制和时空分布原因

RECURRENCE MECHANISM AND TIME-SPACE DISTRIBUTION CAUSE OF LARGE EARTHQUAKES IN XIANSHUIHE FAULT ZONE

岩石接触面在高温高围压下经过几天便烧结起来而有很高但低于原岩的剪切强度。烧结面与主压应力方向夹角大于55—65°时,便不再断裂而沿其它方向剪断。实验最低温压相当地壳10km深,这应是地壳大断裂的上部裂面与下部烧结层的界限深度,受力后便向下延裂,在下部形成震源。这可能是鲜水河断裂带震源在10—25km深重复发生的原因。由带内大震机制解P轴方向与地球自转速率变化趋势的关系、区域残余应力场水平主压应力分布方向与断裂带走向的关系,讨论了带内大震活动时段的原因。由带内裂面烧结条件、残余和现今应力高值区、岩体低强度区及储存弹性应变能高值区的分布,研究了带内大震空间分布原因。

Two contacted rock surfaces are sintered at 350-900℃ temperature and 100-400 MPa confining pressure for 1-35 days, then they have larger shear strength, but smaller than the original one. Under the condition that the angle between (he sintered surface and principal compressional stress is larger than 55°. the sintered surface does not fractured but the shear surface is occurred along the other orientation. The lowest experimental temperature and confining pressure correspond to 10km depth in the crust. Such a depth should be the dividing boundary between the fracture in the upper part and the sintered layer in the lower part of the large fault. After loading, the large fault extends down and forms the earthquake source in the lower part. This is likely the cause of the major earthquake source in Xianshuihe fault zone repeatedly occurred at 10-25km depth in the crust. This treatise has discussed the cause of active time of large earthquakes along this fault zone in accordance with the relation between the direction of P axis of focal mechanism solution of large earthquakes along this fault zone and the change tendency of the Earth's rotation speed as well as the relation between the distributive directions of horizontal principal compressional stress lines of areal -residual stress field and the strike of this fault zone, and has researched into the spatial distributive cause of large earthquakes along this fault zone in accordance with the sintered condition of the fault zone and the distributive areas of higher residual stress, higher present stress, lower strength of rock mass and higher elastic strain energy stored in rock mass.