Conundrum of Sustained Seismicity and Low Deformation in the Koyna–Warna Region, India

ABSTRACT Low-magnitude seismicity observed in the Koyna–Warna region, India, during the past five decades is considered to be triggered by the reservoir impoundment. The area is located in the stable continental region of the Indian plate. However, the causative mechanism of the earthquakes is not known. Here, we present the results of a decade-long continuous Global Positioning System measurements from the region, which imply a tectonic deformation rate of 0.2–0.3 ± 0.04 mm/yr in the region. This is intriguing that such a low rate of deformation, which is significantly less than the average intraplate deformation of the India plate (1–2 mm/yr), is responsible for the seemingly high seismicity in the Koyna–Warna region. Assuming the deformation to be elastic, we estimate a corresponding slip rate of ∼2 mm/yr on the seismologically inferred faults in the region. Interestingly, the annual seismic moment release in the Koyna–Warna region is consistent with the geodetically estimated strain rate, which implies that the current seismicity in the region may be driven by the shallow slip on the faults where the earthquakes are clustered.