用ETAS模型分析自贡矿井注水触发地震

Water injection triggered earthquakes in the Zigong mineral wells in ETAS model

为研究自贡地区矿井注水与地震活动性之间的关系,按地震活动规律将注水区ML1.2以上历史地震活动划分为3个阶段,采用POWELL法反演了各阶段ETAS模型参数。结果表明,不存在注水的第1、2阶段背景地震比例约40%～50%,单个地震序列中余震较少。而在注水的第3阶段,由地震自激产生的余震比例较高(93.1%),而背景地震仅占6.9%,比第1、2阶段都要少,这一结果与已有的认识相矛盾。为此,提出单位时间背景地震的发生率,即ETAS模型参数中的μ值,作为判断注水触发地震的依据。计算结果表明,与前两个阶段相比,第3阶段的确拥有最大的μ值,说明注水对该区地震触发有明显影响。

In order to reveal the relationship between the water injection in mine wells and the seismicity in Zigong,we divide the ML≥1. 2 historical earthquakes into 3 phases according to the seismicity behaviors,and then the ETAS model parameters are inversed by the POWELL method. The results show that Phases 1 and 2 with no water injection have the moderate-to-low ratio of background earthquakes （ 40% ～ 50% ）,and aftershocks are relatively fewer for a single earthquake sequence. In Phase 3 with water injection,the aftershocks triggered by foreshocks dominate this phase （93. 1% ）,while the number of background earthquakes only 6. 9% ,less than Phases 1 and 2,which conflicts with the known conclusion. To resolve this problem,we propose that the occurrence ratio of background in unit time,i. e. the μ value in ETAS model,should be used to an indicator of water injection triggered earthquakes. Compared with the first two phases,Phase 3 has the largest μ value,which illustrates the water injection has an obvious effect in the earthquake triggering.