Reservoir-induced seismicity in the Danjiangkou Reservoir: a quantitative analysis

Reservoir-induced seismicity (RIS) was observed, following the impoundment in 1967 of the Danjiangkou Reservoir in Henan and Hubei provinces in central China. Starting with low-level seismicity, the magnitude increased with increasing lake levels, thereafter culminating in a damaging M 4.7 earthquake in 1973 November. Although the lake levels increased, the seismicity decreased. The spatial and temporal patterns of the RIS show that it was associated with through-going, deep crustal faults, especially in the vicinity of surface exposures of karsts and limestone rocks. There was a systematic increase with time of the calculated hydraulic diffusivity (and hence the permeability) of the fractures associated with pore pressure diffusion. Increases in lake levels over the previous highest levels were directly correlatable with increasing magnitudes of the earthquakes that followed—providing evidence of stress memory in the rocks. The seismicity was associated with increases in diffused pore pressures at hypocentral locations which ranged from < ∼100 to ∼400 kPa for M 1+ to M 4+ events.