Abstract:Using P/S amplitude ratio and P-wave first motion data obtained by the digital telemetered seismic network of induced earthquake monitoring system in the Three Gorges area, we analyze the focal mechanisms of earthquakes occurring in the key monitoring area of the Three Gorges reservoir. The main features are near vertical P axes and pure normal faulting. Water loading and its fluctuation in the reservoir, together with the chemical effects of water, might cause the unstable planes to lose balance, resulting in small earthquakes. This is supported by the focal mechanisms of the induced earthquakes that show oblique P axes, which are different from the regional stress fields and focal mechanisms of the earthquakes that occurred before the first impoundment.
SONG Chen,WANG Dun. Possible Mechanisms of the Earthquakes that Occurred in the Key Monitoring Area of the Three Gorges Reservoir after the First Impoundment[J]. jgg, 2016, 36(7): 625-629.