四川长宁盐矿井注水诱发地震研究

Research of the Earthquakes Induced by Water Injections in Salt Mines in Changning, Sichuan

根据现场调查资料、矿区地质构造资料和数字地震记录,研究了四川长宁盐矿井注水诱发的地震活动。研究发现,2006年4月前矿井注水与出水量相当,地震活动平稳;之后注水量远超过出水量,在注水量和出水量相差较大时,浅层中小地震频次急剧增加。长时间的大量注水可能渗入先存的长宁背斜内的小断裂及微裂缝带,加速附近区域微构造地层的破裂,引发了小震群活动。利用数字地震波形资料计算的Q值显示该地区地下介质较不均匀;小震精定位结果显示震源深度较浅,主要分布在2-3km;震源机制解表明,浅层地震呈正倾滑特征。这些都表现出矿井注水诱发地震活动的某些特征。

This paper studies the earthquake activities induced by water injections in the salt mines in Shuanghe, Changning, Sichuan with the help of the data of on-the-spot investigation, tectonics of salt mining area and digital seismic records. The study finds that, the amount of water injection and drawl in Shuanghe salt mining region were balanced before April 2006 and the earthquake activity was stable. However, shallow small and moderate earthquake numbers increased sharply after the water injection amount was much larger than the water drawl amount. Large injection for a long time may have caused water permeation in the existing small fractures and micro cracks in Changning anticlinal, and accelerated the rupture of micro tectonic formation in near regions, which led to the small earthquake swarm activities. Q value calculated by using digital earthquake records indicates that the medium is relatively inhomogeneous in this area. The result of small earthquake location accurately shows that sources are relatively shallow and concentrate at 2km to 3km depth. Focal mechanism solutions reveal normal dip-slip characteristics of shallow earthquakes. All of these are some characteristics of the activity of induced earthquakes by water injection.