Annual Periodicity in the Seismicity and Water Levels of the Koyna and Warna Reservoirs, Western India: A Singular Spectrum Analysis

Association of earthquakes with dams and reservoirs has been reported in several cases worldwide. The Koyna region in western India is one such famous example where earthquakes continue to occur even after 50 years of reservoir impoundment and after the 1967 Koyna earthquake (M 6.3), the largest reported earthquake associated with a reservoir. We analyzed the seismicity data from January 2005 to June 2012 in the Koyna-Warna region as recorded by a local seismic network. We performed a singular spectrum analysis, which shows that water level series has dominance of variance for annual periodicity. For the earthquake time series, a particular zone of earthquakes located close to the Warna reservoir shows predominance of annual frequency, suggesting a compelling relation between seismicity of this zone and reservoir water level changes. The lower-order periodicities in the earthquake time series suggest that additional processes (other than reservoir water level changes, which are not well understood and hence need further investigations) also contribute to earthquake activity throughout the year.