Seismicity of region around dams in North West India

The collision of Indian and Eurasian continents caused large scale deformation and high seismicityof vast areas of both continents in the geological history. The North-West portion of the Himalayan arc which is lyingunder the rupture zones of Kangra earthquake of 1905, Uttarkashi earthquake of 1991 and Chamoli earthquake in 1999,has experienced many earthquakes of magnitude 6 and above. The region of North-West India between 30.0º - 35.0ºNorth and 73.0º - 79.0º East is, therefore, under intense investigations by various scientists since the origin of theHimalayas. India Meteorological Department had opened thirteen seismic observatories in early sixties for monitoringof earthquake activities in and around Bhakra, Pong, Pandoh dams in Punjab / Himachal Pradesh and Salal dam inJ&K on specific demand of the dam authorities. These observatories have recorded the earthquakes occurred in thisregion having magnitude even less than 2. The data collected for the last two decades is very useful for the scientiststo investigate seismicity and tectonics of the Himalayas. The present study could locate the regions which areseismically most active and also the region of seismic gap. Thus present study confirms association of seismic activityin the region with two major fault systems called Main Boundary Thrust (MBT) and Main Central Thrust (MCT).Comparative seismic activity within 100 km from each dam, reveal that most active region was around Pong followed byPandoh, Bhakra and Salal dams. The temporal variation of b-values for the whole period also shows that low b-valueanomalies are usually followed by large earthquakes of M > 5.5. No definite conclusions could be drawn with regard tothe relationship between the observed seismic activity around the dam sites with the corresponding water levelfluctuations in the reservoirs.