流体触发2013年广西平果震群活动机理研究

Research on Mechanism of Fluid Triggering 2013 Pingguo Earthquake Swarm in Guangxi

2013年广西平果地区发生浅源震群活动,目前对于该震群活动的触发机制还存在争议。通过研究区构造裂隙渗透性调查,发现NW向和近EW向断层或节理是深浅流体交换的主要通道,浅表流体沿通道下渗形成深部地下流体带,震前排泥库附近30 m高的壅水使地下流体的温压条件发生变化,从而加速流体向右江断层带NW向次级断层和近EW向断层内部渗透。结合地震波形初动记录、ETAS模型μ值检验、震源机制解等,推断平果震群是构造因素以及流体参与并触发断层浅部活动的结果,其中震源深度大于3 km的地震主要是由于右江断裂带上盘构造背景应力较高且应力集中等原因引起,而小于3 km的浅部震群活动则主要是由以下2个因素共同作用所触发:(1)深部流体渗透作用改变了断层结构面上的原有应力状态,降低了断层面的有效正应力和断层的有效强度,增强了断层深部流体压力,加速了浅部断层局部解锁滑动;(2)浅表流体与深部承压流体的水力联系、沟通和交换,改变了断层内部的温压条件和应力环境。

In 2013,an earthquake swarm with shallow depth occurred in Guangxi Pingguo,and its triggering mechanism is still discussed.According to the survey on the permeability of structural fissures in the study area,we found that the faults or joints in NW and EW were the main paths for exchanging between the deep and the shallow fluids,and the shallow fluid infiltrated along the paths to forming the underground fluid zone.The 30 m high tailing pond retained water around sludge drainage before the earthquake changed the temperature and press of original underground fluid,which hastening the fluid flow to the secondary fault in NW of Youjiang fault zone and faults in EW.Combined with initial motions of seismic wave,μ-value test of the ETAS model and focal-mechanism solutions,we induced that the 2013 Pingguo earthquake swarm was caused by tectonic factor and the fluid participated in and triggered shallow faults.The earthquakes whose focal depth is above 3 km were caused by the high stress and stress concentration on the hanging wall of the Youjiang fracture zone.The other earthquakes whose focal depth is under 3 km triggered by following factors:①The osmosis of deep fluid changed the original stress system and reduced the available normal stress and effective strengthened of faults surface.Also it improved the press of deep fluid in the fault zone and hastened the local unlocking and slipping of shallow faults.②The hydraulic contact,communication and exchanging between the shallow and deep fluids changed the temperature,press and stress environment.