昆仑8.1级地震同震形变特征及其对响应地震活动的制约机制

Coseismic Deformation features of the Kunlun Ms S. 1 earthquake and Its constraint Mechanism to Response Aftershocks

本文定义"响应地震"的概念统一表述昆仑山口西8.1级地震所引发的主破裂两侧临近构造及部分块体边界上的显著地震活动.其主体活动区域集中在昆仑地震主破裂的西南侧和东北侧及祁连山断裂.同时,地壳运动在主破裂北侧的甘青块体中西部出现与背景运动场反向的特征性变化,祁连山断裂出现应变弱化.弹性位移-应力阶跃模型模拟结果显示,昆仑地震造成其东北侧甘青块体中西部地壳运动的反向运动(相对背景场).并形成东北部和西南部两个体应变张性区域,绝大部分响应地震都发生在应变张性区中和块体张性边界上.这种强烈挤压剪切背景中出现的相对松弛状态与昆仑地震后青藏块体地震弱活动背景中出现的显著活跃的响应地震活动的正相关性可能反映了断层约束状态的相对减弱对滑动的触发作用.说明在考虑地震发生条件时,不能只着眼于应力场是否增强,断层摩擦强度,或更广义地说,构造约束条件的变化也是一个不容忽视的重要因素.

The Kunlun M,8. 1 earthquake placed a premium on distinct response earthquakes along raptures near the main fracture and boundary of the block. The main regions are located in northeast and westsouth side of the Kunlun fault and Qilianshan fault. Meanwhile, there is a relative reverse motion of crust relative to background crust movement,and is reJaxe change of compression on the Qilian rupture. The simulation result of elastic displacementstress jump model shows that there is reverse movement of crust relative to background in the mid-west area of the Ganqing block which sits at northeast side of Kunlun rupture by the Kunlun event,where two regions of dilation were produced. Most of response earthquakes occurred in the dilation inner-area of block and dilation boundary of block. One side is this positive pertinence, between relative relaxation change of strain in strong compression-shear background and active regional reponse earthquakes happened in whole weakening seismicity of Tibet plateau,which may suggests the triggering action due to weakening restriction on faults. It suggests that, when considering the reasons of crack＇s happening, not only the stress level, but also the friction state, or restriction condiction on the fault is an important factor,too.