Seismicity of region around dams in North West India

Abstract

The collision of Indian and Eurasian continents caused large scale deformation and high seismicity
of vast areas of both continents in the geological history. The North-West portion of the Himalayan arc which is lying
under 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 - 35.0º
North and 73.0º - 79.0º East is, therefore, under intense investigations by various scientists since the origin of the
Himalayas. India Meteorological Department had opened thirteen seismic observatories in early sixties for monitoring
of earthquake activities in and around Bhakra, Pong, Pandoh dams in Punjab / Himachal Pradesh and Salal dam in
J&K on specific demand of the dam authorities. These observatories have recorded the earthquakes occurred in this
region having magnitude even less than 2. The data collected for the last two decades is very useful for the scientists
to investigate seismicity and tectonics of the Himalayas. The present study could locate the regions which are
seismically most active and also the region of seismic gap. Thus present study confirms association of seismic activity
in 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 by
Pandoh, Bhakra and Salal dams. The temporal variation of b-values for the whole period also shows that low b-value
anomalies are usually followed by large earthquakes of M > 5.5. No definite conclusions could be drawn with regard to
the relationship between the observed seismic activity around the dam sites with the corresponding water level
fluctuations in the reservoirs.