Seismicity Impact in Patan Taluka, District Satara, Maharashtra

The continued seismicity in the Koyna region has had the maximum impact in the Patan Taluka of the Satara District in Maharashtra within 30 km radius from the epicentral region of earthquakes. The Government of Maharashtra has undertaken rehabilitation of the villages which have suffered the damage and are threatened also by the collapsing edges of the overhanging lateritic cliffs. On the M.M. intensity scale the damages suffered by the settlements and lateritic plateau would indicate an intensity between VII and VIII. A high acceleration, maximum of 0.1 g (100 cm/sec 2 ), is inferred for the soil profiles and alluvial tracts, loose gravel colluvium, river terraces material and weathered basalts on which the settlements are located. The continued seismicity around Koyna reservoir is often referred to as "reservoir induced", but such a mechanism is considered valid only for earthquakes originating from very shallow depths. For earthquakes whose hypocenters lie far below in the basement rocks (depth >3 km), the magnitude frequency relationship (26 years period) is similar to that observed in any tectonically active regions. It seems that the seismicity is related more to the reactivation of basement faults, reflected also in the overall geomorphological features of the region.