PREDICTION OF RESERVOIR INDUCED SEISMICITY

Abstract

In the present study the probability of occurrence of the Reservoir Induced Seismicity (RIS) has been estimated for four dams located in Himalayan region and Peninsular India, namely, Tehri dam, Ram Ganga dam, Indira Sagar dam and Sardar Sarovar dam. A prediction model based on discriminant analysis developed by Beacher and Keeney (1982) has been adopted for the purpose of estimating the occurrence probabilities of RIS. The model considers five attributes viz., depth, volume, stress state, fault activity and geology of reservoir sites and allows estimating occurrence probability of RIS adopting independency and dependency between the attributes. Probability of occurrence of RIS at Tehri dam located in the Garhwal Lesser Himalaya is estimated as 0.49 assuming independency of attributes and 0.53 assuming dependency between the volume and geology at the reservoir site. These values are high because Tehri reservoir is a very deep reservoir: The risk of occurrence of reservoir induced earthquake as a random event is high in Tehri region. The Ram Ganga dam, located in the Kumaon Lesser Himalaya, indicates an occurrence probability of 0.31 considering independency between the attributes and 0.44 assuming dependency between the depth and geology at the reservoir site. The Indira Sagar and Sardar Sarovar dams located in Peninsular India exhibit occurrence probability as 0.25 and 0.16 considering independency between the attributes. The estimated maximum magnitudes of induced earthquakes for Tehri dam, Ram Ganga dam and Sardar Sarovar dam are 6.3, 5.86 and 3.06. The risk of occurrence of induced earthquakes both in terms of occurrence probability and size of the earthquake is more for dams falling in the Himalayan region as compared to dams located in the Peninsular India.