2014秭归4.5、4.7级地震前小震活动特征研究

2014-03-27、30湖北秭归4.5、4.7级地震前,震中区附近发生过多次微小地震活动。双差精定位显示,这些小震集中分布在仙女山断裂北段西边次级小断裂附近(区域一)和北端端部(区域二)。结合近场地震波谱分析和区域地质构造特征认为,区域一的微小震主要为浅表塌陷事件,区域二的多数为构造地震事件。将区域二15次ML1.2以上事件震源机制解参数统计结果与该地区3次4级以上主震震源机制比较显示,两者的节面走向均为NNW和NE,力轴(P轴和T轴)的方位与倾角也基本一致,总体上均与区域应力场方向基本一致,反映了两者受力方式具有一致性,但两者的破裂滑动方式有差异,可能与仙女山断裂受库水作用活化的影响有关。

Study of Small Earthquakes Activity Characteristics before the Zigui 4.5, 4.7 Earthquake in 2014

Many micro-small earthquakes occurred near the epicenter before the Zigui 4.5 and 4.7 earthquakes on Mar 27, 30 in 2014. The D-D location results showed these earthquakes distributed near the sub-fault of the west of the Xiannüshan fault (area one) and the north end of this fault (area two). According to spectral analysis of the near-field seismic wave and characteristics of the regional geology and tectonics, we believe that small earthquakes in the area one were mainly shallow collapse events and earthquakes in the area two were tectonics seismic events. Comparing the statistical results of the focal mechanisms parameters of 15 small earthquakes in the area two to focal mechanisms of the 3 main shocks in this area, it shows that both plane strikes are NNW and NE, and that the azimuth and dip of force axes (P and T axes) are also basically the same, i.e., wholly consistent with the orientation of the regional stress field. These results reflect that the two force patterns have some consistency, but that there were differences on the rapture mode, which may be related to the re-activity of Xiannüshan fault by the effects of the water in the Three Gorges reservoir.