Seismicity around Dhamni Dam, Maharashtra, India

Abstract.

—Dhamni Dam (height 59 m, capacity 285 Mm³) was constructed about 100 km north of Mumbai (Bombay), India over the Deccan flood basalt and across the Surya River. The filling of the reservoir started in 1983. Construction of the dam was completed in 1990. However for want of environmental clearance, the maximum water column height in the reservoir since 1988 has been 45 m (8 m short of the maximum possible, 53 m) with the volume of water in the reservoir being 175 Mm³. The first phase of seismicity started in August 1984, soon after the reservoir reached a 22.5 m depth over the river bed level, and the increased level of seismicity continued for two years, when 605 shocks of M≥ -1.7 to 2.5 were recorded. During 1987–93, there were only a few shocks. Seismicity rejuvenated in 1994 when over 2000 shocks of M≥ -1.7 to 3.8 occurred, including 20 shocks of M≥ 3.0 which occurred during the months of January–February and August–September. Seismicity has continued at a low level during 1995 and 1996. The hypocenters are located in a volume of 10×10×10 km³ situated just south of the reservoir along the NW trending Kalu-Surya fault. Correlation of a space-time pattern of seismicity with reservoir filling and the seismic characteristics like b value, foreshock-aftershock pattern and decay rate of aftershocks indicate that the seismicity is reservoir induced.