KOLKATA: The recent earthquakes in different parts of India, albeit of small magnitudes, have occurred due to foreshocks and swarms, a top official of the Geological Survey of India (GSI) said, warning that frequent tremors were a matter of concern in the subcontinent, where several areas are prone to major seismic activities.
Dr Sandip Som, the deputy director general of GSI, also said that foreshocks — mild tremor preceding earthquakes — or swarm activities — series of earthquakes — indicate release of tectonic stress and strain during the continuous deformation process, and a detailed study of these jolts could help predict if a significant seismic event is in store.
“These minor earthquakes are mainly clustered in the north-eastern and north-western Himalayan region, around the Delhi-National Capital Territory (NCT), western Gujarat and Western Maharashtra areas which have been demarcated as seismic zones IV and V,” the geologist told PTI on Sunday.
In the past, too, low-magnitude earthquakes have been recorded in these regions, he said.
According to the GSI scientist, earthquakes in the north-eastern and north-western Himalayas occur along the plate convergence zones — between India and Eurasia.
“In the Delhi-NCT region, the spatial distribution of seismicity shows seismic activity-concentration mainly in three places — west of Delhi (near Sonipat), along the Mahendragarh-Dehradun subsurface fault and Delhi Subsurface Ridge,” he said.
“Similarly, in Western Gujarat, the seismic concentration is located near the intersection between Rajkot-Lathi lineament and neo-tectonic Kutch mainland fault. There is an east-west flexure of Indian lithosphere in the Western Ghat Escarpment,” Dr Som said.
Explaining the reason behind the frequent tremors, the geologist said any earthquake depends on the strain and stress build-up of an area.
“Main strain and stress build-up areas have been noted along the convergence zone between Indian and Eurasian plates. Due to continuous plate movement, stresses build up in this area. Moreover, there are around 30 water reservoirs along the WGE. Enhanced water load in the reservoirs increases pore pressure and stress, triggering earthquakes,” he said.
Incidentally, the GSI has deployed 30 permanent GPS stations across the country to monitor tectonic plate movements and develop a strain map to identify potential hazardous zones.
“Work is under progress and likely to be completed its first phase very soon. We will also carry out seismic microzonation (process of sub division of region) and active fault studies to evaluate potential geological vulnerable seismic sites,” he said.



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