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.
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