三峡库区巴东地震(Ms5.1)成因机制及次声波信号

2013年12月16日三峡库区巴东发生M_s5.1地震.根据eigen-6c2模型研究了巴东地区的8-638阶卫星重力异常, 结果表明: 该地区场源深度为10 km的地壳为局部重力低异常, 反映了该处物质密度较周围偏低, 形成低密度层.同时, 研究了该地区速度结构剖面, 结果表明: 巴东地区地壳5~9 km及10~15 km深处存在上下两个低速层, 上部低速层与水库渗水有关, 下部低速层与地幔热流体的上涌有关.低密度层和低速层的确定为韧性流变层的存在提供了证据.巴东地震是地壳深部能量的长期集聚与突发释放, 属构造地震.然而, 库水下渗引起的上部低速异常降低了断层活动的阈值, 震前库水载荷的变化对此次巴东地震的发生起到了触发作用.通过对比次声波和地震波, 我们得出次声波仪记录到的异常信号为本地次声波. 

Seismogenesis of Badong Earthquake (M s 5.1)in Three Gorges Reservoir Area and Infrasound Anomaly

On 16 December, 2013, an earthquake of M_s5.1 occurred in the Badong County, the Three Gorges reservoir area, China. Using the EIGEN-6C2 model, the satellite 8-638 order gravity anomalies in this area were studied. The results show that there is a regional low gravity anomaly beneath Badong area at 10 km, which may imply that rock density this area of is lower than its surroundings. Meanwhile, the profiles of crustal velocity structure of this area indicate the existence of two low-velocity layers at depth of 5-9 km and 10-15 km respectively. We believe that the upper layer is closely related to the reservoir seepage and the lower layer may result from the upwelling of the mantle hydrothermal fluid. The low-density layer and the two low-velocity layers provide an evidence for the existence of a possible ductile layer. The occurrence of Badong earthquake is due to the long-term energy accumulation and abrupt release at the deep crust, thus it is a tectonic earthquake. The low-velocity anomaly in the upper crust caused by reservoir seepage decreased the threshold value of fault activities and the change of water load of this reservoir might trigger the Badong earthquake. By comparing the infrasound with seismic waves, we conclude that the infrasound anomalies recorded by the infrasound monitor array are local infrasound.