Abstract：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.
WU Haibo,SHEN Xuelin,DU Chengchen et al. Study of Small Earthquakes Activity Characteristics before
the Zigui 4.5, 4.7 Earthquake in 2014[J]. jgg, 2015, 35(5): 751-757.
