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In order to reveal the relationship between water injection in mine wells in the Zigong area and seismicity,we divide the historical earthquakes of ML≥1. 2 into 3 phases according to seismicity behavior,and the ETAS model parameters are then inversed by the POWELL method. The results show that phase 1 and 2,in which there is no water injection,have moderate-to-low ratio of background earthquakes ( 40% ～ 50%),and aftershocks are relatively less for a single earthquake sequence. In phase 3,where there is water injection, the aftershocks triggered by foreshocks dominate (93. 1%),and background earthquakes amount only to 6. 9%,less than those of phase 1 and 2. The results conflict with the existing cognition. To resolve this problem,we propose that the occurrence ratio of background earthquakes in unit time,that is,the μ value in ETAS model is used as an indicator of water injection triggered earthquakes. Compared to the first two phases,phase 3 has the largest μ value,which illustrates that the water injection has an obvious triggering effect on earthquakes of this region.
In order to reveal the relationship between water injection in mine wells in the Zigong area and seismicity, we divide the historical earthquakes of ML ≧ 1. 2 into 3 phases according to seismicity behavior, and the ETAS model parameters are then inversed by the POWELL method . The results show that phase 1 and 2, where there is no water injection, have moderate-to-low ratio of background earthquakes (40% ~ 50%), and aftershocks are relatively less for a single earthquake sequence. , where there is water injection, the aftershocks triggered by foreshocks dominate (93.1%), and background earthquakes amount only to 6.9%, less than those of phase 1 and 2. The results conflict with the existing cognition. To resolve this problem, we propose that the occurrence ratio of background earthquakes in unit time, that is is, the μ value in ET indicator is water injection triggered earthquakes. Compared to the first two phases, phase 3 has the largest μ value , which illustra tes that the water injection has an obvious triggering effect on earthquakes of this region.