强震前断裂亚失稳阶段及失稳部位的特征研究--以新疆南天山西段为例

Study on meta-instability stage and instable section of the fault before strong earthquake: Taking western section of Southern Tianshan as an example

我们把处于亚失稳阶段的断裂简称为亚失稳断裂,亚失稳阶段是断层临近失稳的最后阶段,识别这个阶段并判断出地震最终的发生位置是一个关键的科学问题.参考实验室关于断层亚失稳应力状态的研究结果,以6.8级以上地震为研究的目标地震,提出判定具备发生6.8级以上地震的亚失稳断裂研究方法:(1)构造区Benioff应变积累支持6.8级以上地震发生;(2)从高应变积累构造区中找出高应变积累且应变开始缓慢释放的断裂;(3)区分断裂的积累段和释放段,根据断裂释放段的协同化程度判定其是否处于亚失稳阶段,寻找失稳部位;(4)断裂Benioff应变是否符合加速释放模型,分析亚失稳断裂发震的紧迫性.本文以南天山西段为研究区,使用亚失稳断裂判定方法对2008年10月5日乌恰6.8级地震进行回溯性研究,结果显示卡兹克阿尔特断裂在主震前具备上述4个条件,预测取得较好的效果;进而使用该方法对研究区现今应力状态进行探索性预测研究,发现目前柯坪断裂符合亚失稳状态条件的前三条,需关注该断裂的地震活动.

We have referred to the fault in meta-instability stage as the meta-instability fault. Meta-instability stage is the last stage of instability. The important scientific problem is to identify this stage and determine the location of earthquake. Based on the characteristics of metainstability stage which is observed in laboratory experiments, we propose a method for determining the recta-instability fault with Ms≥6.8 earthquake：（1） The accumulation of Benioff strain in tectonic zone supports the occurrence of Ms≥6.8 earthquake. （2） Find the fault with high strain accumulation where the strain began to release, and the fault is divided into accumulation and release segment. （3） We judge whe.ther the fault in the Meta-instability stage according to the degree of collaborative activity. （4） Whether the Benioff strain is consistent with the accelerating seismic patterns. In this paper, we take the Western section of Southern Tianshan as the study area, use meta-instability fault method for the retrospective research on Wuqia Ms6.8 Earthquake on October 5,2008. The results show that the Kazkeaerte fault had these 4 conditions before the mainshock, the prediction has achieved good results. We use this method to study the predictability in the study area, found that the Kalpin fault satisfies the first three conditions. We should pay attention to the seismic activity of Kalpin fault.