Seismicity pattern for earthquakes near Bhatsa Reservoir, India

Abstract

Abstract The three earthquakes ( ML > 4.0) and aftershocks near Khardi village, Thane District, Maharashtra State, India which occurred close to the Bhatsa Dam after May 1983 have been relocated by choosing the best of seven trial crustal velocity models and discussed in relation to their source mechanisms. The earthquakes in the region are attributed to the northwesterly oriented shallow dipping thrust fault and northeasterly lineaments. Well marked “seismic quiescence” was observed before the largest aftershock of January 1984. The statistical criteria, to distinguish reservoir-associated seismicity from normal tectonic earthquakes are discussed in comparison to the Koyna and other dams. It has been found that the temporal variation of microearthquakes in the Koyna region from 1967 to 1987 shows the slowest rate of decay in Omori's law of aftershocks as t−0.15, which distinguishes it as a unique case of reservoir-associated seismicity. Using this and the seismicity pattern during the last 20 years, a schematic model has been proposed for the trend of seismic activity near the Koyna region. According to this model, the magnitude of the largest future earthquake near the reservoir may not exceed that of the largest aftershock namely magnitude 5.0, which would eventually be gradually decreasing with time at progressively larger intervals. Extension of this model to the Bhatsa region suggests that the magnitude of the largest earthquake in that region would not exceed 4.0 in the near future.