水库诱发地震与构造地震震源参数特征差异性研究——以龙滩水库为例

首先讨论龙滩库区水库蓄水与地震活动之间的关系,发现龙滩水库诱发地震特征十分明显,地震共分5丛呈丛集分布.利用库区架设的24个固定和流动台站记录的数字记录资料,在研究得到龙滩库区非弹性衰减和台站场地响应的基础上,精确测定得到了该地区总共1616个ML≥0.1级地震的震源参数,比较了水库诱发地震与构造地震震源参数特征的差异,得到了以下主要结论:1)龙滩水库地震活动与水库蓄水关系密切,不同蓄水阶段5丛的地震活动状态不同,局部断裂构造发育以及岩石透水性能影响着地震活动对蓄水过程的响应.2)龙滩水库诱发地震的地震矩M0随震级ML的增大而增大,两者之间存在较好的线性关系,统计关系为LogM0=1.07 ML+10.17.应力降与地震大小之间的关系和Nuttli的板内地震为增加应力降(ISD)模型的结果比较吻合,统计关系为LogΔσ=0.71 ML-2.89.3)龙滩水库地区地震辐射能量和地震视应力均随震级的增大而增大,后者意味着大地震是比小地震更高效率的地震能量辐射体.4)总体上不同丛地震应力降水平存在差异.地震应力降空间分布上与库水深度有较好的一致性,即库水深的区域应力降水平高.5)与同震级的构造地震相比,水库诱发地震的应力降值比前者明显偏低,大约小10倍.这可能是由于水库蓄水造成地下介质孔隙压力增大或者水的润滑作用,从而导致在一个比较低的构造应力情况下发生水库诱发地震.

Differences existing in characteristics of source parameters between reservoir induced seismicity and tectonic earthquake——a case study of Longtan reservoir

In this text,we firstly discussed the relationship between the water filling and seismicity in Longtan reservoir and found that the characteristic of reservoir induced seismicity was very apparent in Longtan reservoir and these epicenters mainly distributed in 5 clusters.Digital seismic data recorded by 24 fixed and temporary stations located around the reservoir were used to study the characteristics of anelastic attenuation in this region and to obtain the site responses.After that,source parameters of 1616 earthquakes with magnitude bigger than 0.1 were calculated and the differences existing in characteristics of source parameters between reservoir induced seismicity and tectonic earthquake were discussed.Our results show that(1) Seismicity in Longtan reservoir has strong relationship with the water filling of reservoir and the activity status of seismicity for these five clusters are various in different water filling period.The response of seismicity to the water filling process is affected by the development of local faulted structure and the water permeability of the rock.(2) Seismic moment M0increases with increasing magnitude ML in Longtan reservoir and their statistical relationship is LogM0=1.07ML+10.17.Relationship between stress drop and magnitude is consistent with the result gained by Nuttli that intraplate earthquake follows the ISD model,with a statistical relationship LogΔσ=0.71ML-2.89.(3) Radiated seismic energy and apparent stress in Longtan reservoir all increase with increasing magnitude,indicating that the big earthquake is a radiator of seismic energy with more efficient rather than small earthquake.(4) In general,there are some differences in stress drop for different cluster.The distribution of stress drops has a good consistence with the water depth of reservoir,with high value of stress drop in deeper water depth.(5) Stress drops of reservoir induced seismicity are smaller than that of tectonic earthquake with same magnitude apparently,about 10 times.These results maybe indicate that the reservoir induced seismicity can occur with a lower tectonic stress due to the high hole pressure of the underground medium and the effect of the water lubrication.