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在前期严重干旱的背景下,2010年6月27～30日广西西北部出现大暴雨过程,大范围积水成涝.降雨量最大的凌云、凤山交界于6月28日17时开始出现密集的微震活动,形成显著的震群事件.自6月28日至7月15日共记录地震2739次,其中2～2.9级(M_L,下同)41次,3级以上地震3次,最大为7月1日10时27分3.2级地震.凌云—凤山震群微震活动与暴雨过程具有明显的时空相关特性,在时间上略有滞后.震中附近大范围内碳酸盐岩类岩溶等浅层构造非常发育,震中位于Nw和NE向断裂交汇区域,断层破碎带的存在,成为流体下渗的优先通道.震群空间分布集中、震源深度浅,63%地震的空间范围(半径)或震源深度小于1.6 km、88%的小于2.5 km,98%的小于3.4 km.较大地震震相特征显示,震群活动有流体参与并显示岩溶塌陷特征.由于流体沿断层面的快速下渗,微震似有沿断裂带展布的特征,但较大地震震源机制结果不支持震群活动缘于断层构造运动的猜想.位于震中区流动台记录的大多数地震的垂直向初动向下,且较小地震初动向下的比例更高,意味着大多数微震活动可能缘于岩溶塌陷或裂隙闭合.基于传染型余震序列模型(Epidemic Type Aftershock Sequence model,简称ETAS模型)的定量检测结果显示,流体对凌云—风山震群的触发作用非常强烈,同时震群地震自激发亦较强.基于孔压的一维扩散方程,模拟了流体渗透导致不同深度孔压随时间的变化,结果显示,流体渗透导致的孔压增加是凌云—风山震群发生的主要力学动因.在上述研究的基础上,初步提出凌云风山震群可能的发震机理.
In the context of severe drought in the previous period, a heavy rainstorm occurred in northwestern Guangxi Province from June 27 to June 30, 2010, causing floods and waterlogging in a large area. At the junction of Lingyun and Fengshan, with the heaviest rainfall, began to appear densely at 17:00 on June 28 A total of 2739 earthquakes were recorded from June 28 to July 15, of which 2 to 2.9 (M_L, the same below), 41 earthquakes of magnitude 3 and above, with a maximum of 7 On January 1, at 10:27:27, the magnitude earthquake of Lingyun-Fengshan earthquake swarm has obvious spatiotemporal correlation characteristics and slightly lags behind in time, and the carbonate rock karst and other shallow layers The structure is very well developed and the epicenter is located at the junction of Nw and NE fractures, and the fault fracture zone is the priority channel for fluid seepage.The spatial distribution of the swarm is concentrated, the focal depth is shallow, the spatial range (radius) of 63% of the earthquakes, Less than 1.6 km, 88% less than 2.5 km and 98% less than 3.4 km. The characteristics of larger seismic facies show that fluid swarm activities are involved in fluids and show karst collapse characteristics. Due to the rapid infiltration of fluid along the fault plane, There are features distributed along the fault zone, but the result of a larger earthquake focal mechanism does not The earthquake-holding group activity is due to the conjecture of fault tectonic movement.Most earthquakes recorded by the mobile stations located in the epicenter area have a lower initial vertical motion and a lower proportion of the initial earthquakes, indicating that most microseismic activity may be due to Karst collapse or fracture closure.The quantitative detection results based on the Epidemic Type Aftershock Sequence model (ETAS model) show that the fluid has a very strong triggering effect on the Lingyun-Fengshan earthquake swarm, The results show that the increase of pore pressure caused by fluid infiltration is the main mechanical reason for the occurrence of Lingyun-Fengshan earthquake swarm. Based on the one-dimensional diffusion equation of pore pressure, the variation of pore water pressure at different depths with time is simulated. Based on the above studies, the possible seismogenic mechanism of Lingyun wind-shakes swarm was proposed.