Statistical parameters of seismicity induced by the impoundment of the Three Gorges Reservoir, Central China

Induced seismicity has been observed in the Three Gorges Reservoir (TGR) area, central China, since its impoundment in May, 2003. Data from a local seismic network in the TGR area and a temporal network allow us to obtain a detailed picture of the spatio-temporal distribution of earthquakes in the Badong area, in which earthquakes are clustered. Statistical parameters, namely the seismic b-value, spatial correlation length, and fractal dimension of the hypocentre distribution, as an integrated set, are investigated and taken as indicators to divide the seismicity in the study area into typical stages. Epidemic-type aftershock sequence modelling, which is useful for extracting possible fluid signals from earthquake occurrences, is applied to the data set. The temporal variations in the parameters indicate a long-term increasing and diffusing stress until the present. Thus, much more attention should be given to seismic activity in the TGR area. The largest earthquake (M5.1), which was followed by aftershocks, a large fraction of which were Omori-type, primarily resulted from a triggered fault movement. In the M4.3 earthquake sequence, both Omori-type seismic triggering and reservoir triggering are statistically important. After the Omori-type aftershocks (which accounted for a small fraction (<20% in total) of earthquakes) are removed, the forced seismic rate is correlated with the water level of the reservoir, indicating that most of the small earthquakes were induced by the reservoir.