关键词: 龙滩水库地震, 震源机制解, 应力场, 水库诱发地震机理

Abstract: The FOCMEC method was adopted to resolve focal mechanisms for earthquakes occurring from Sep.2006 to the end of 2008 in the range of Longtan reservoir by using the first P polarization and SH/P amplitude ratio from earthquake waveforms recorded by the Longtan reservoir seismic network. Then,the stress field of the reservoir area was inversed.According to the results,most of the M_L≥2.0 earthquakes are of thrust faulting since the impoundment in Oct.2006.The stress fields in both the cluster A and B are oriented in NWW-SEE direction and almost horizontal,indicating that the horizontal compressive stress is still the dominant stress after the impoundment,and the dip angle of the maximum principal compressive stress is more horizontal than that before impoundment.However,the middle and minimum stress axes are somewhat inconsistent in the two clusters,which indicates the local disturbance of stress field.The genesis of reservoir induced earthquake is supposed as the coupling of pore pressure action with the fluid lubricating and weakening action under the loading,whereas the increase of shear stress due to water loading is not the causation of reservoir induced earthquake.

Key words: Longtan reservoir induced earthquake, focal mechanism, stress field, mechanism of reservoir induced earthquake