研究中强地震前中小地震震源机制变化的一种方法  

Analyzing Changes of Focal Mechanism of Small-moderate Earthquakes before a Moderate-strong Earthquake

作　　者：荣代潞[1] 

机构地区：[1]中国地震局兰州地震研究所,甘肃兰州730000

出　　处：《地震工程学报》2014年第2期286-291,共6页China Earthquake Engineering Journal

基　　金：中国地震局老专家科研基金(201329)

摘　　要：定义了“P轴分布集中度”用以研究中强地震前中小地震震源机制变化。利用祁连山中东段地区布设的中法微震数字监测台网多年的监测资料和甘肃数字监测台网的资料，使用P波和S波初动和振幅比联合反演方法反演了两次中等地震前震源区附近地区中小地震震源机制解和发震应力场；利用“P轴分布集中度”这一参数分析研究了这两次中等地震前中小地震震源机制和发震应力场的时间变化。结果表明，震前1～2年中小地震震源机制解P轴开始集中，在震前集中到大约与主震震源机制的发震应力场一致。In this paper a parameter called ＂concentration ratio of distribution of P axis＂ was de- fined to analyze the variation of focal mechanisms of small earthquakes before a moderate-strong earthquake. This parameter shows the dynamic change of the direction of the P axis in the seismogenic process. In this paper, we use two moderate-strong earthquake examples, namely the Jingtai earthquake of on Jun. 6,2000 and the Sunan earthquake of on March 30,2008. We invert the focal mechanism solutions and the seismogenic stress field using the joint inversion method of first motion and amplitude ratio of P and S wave for small events before the two moderate-strong earthquake examples. The data used are from the networks set by China and France and the Gan- su digital monitoring network. We study time-varying characteristics （prior to the two earthquake examples）using the parameter ＂concentration ratio of distribution of P axis＂. The results show that the P axis of the focal mechanisms for events begin to concentrate one or two years before the main earthquakes and in accordance with the main earthquakes＇ source mechanism just prior to the main earthquake. The concentration ratio of distribution of P axis prior to the Jingtai earth- quake varies regularly;moreover,the parameter prior to the Sunan earthquake began to show con- centration from the beginning of 2006, whereas the concentration ratio decreases from the begin- ning of 2007 and increases a greater degree by the end of 2007 until the main shock occurred. This could potentially be due to the singularity of the seismogenic fault structure of the Jingtai earthquake,the location stress field would be regionally adjusted during the concentration process and followed by strengthening of the local stress field, which makes the source mechanisms of medium and small earthquakes uniform.

关 键 词：P轴分布集中度 震源机制解 祁连山中东段地区 发震应力场变化 

分 类 号：P315.75[天文地球—地震学]