Garhwal-Kumaon segment most vulnerable to quakes

Bengaluru, November 9 

The Garhwal-Kumaon segment of the north-west (NW) Himalayas is seismically the “most vulnerable section” of the region with a potential to generate great earthquakes, warns a new study by researchers from multiple institutions in the country.

Their findings, reported in the journal “Earth and Planetary Science Letters”, is based on the analysis of five years (2013-2018) of continuous GPS measurements from 28 stations located in the Garhwal-Kumaon Himalayas and the adjoining Indo-Gangetic plains.

Lifted by the subduction of the Indian tectonic plate under the Eurasian Plate, the Himalayan mountain range runs in an arc, about 2,400-km long, separating the plains of the Indian subcontinent from the Tibetan Plateau.

Partly in India and partly in western Nepal, the NW Himalayas had not experienced a great earthquake since at least 1505, Vineet Gahalaut, director of the National Centre for Seismology, New Delhi, and corresponding author of the paper, said.

An analysis of GPS measurements of crustal deformation suggested “strong seismic coupling” underneath the Garhwal-Kumaon region, he said. Strong inter-plate coupling means the fault below Garhwal-Kumaon segment is “locked” and capable of accumulating stress. The width of the coupled region, according to the report, is estimated to be about 85 km.

This strongly-coupled region must have accumulated a “slip” of more than 7 metre since the last earthquake in 1505 “which is enough to produce a great earthquake in the region”, the researchers claim. Slip is the relative displacement of formerly adjacent points on opposite sides of a fault.

According to their report, GPS measurements found the convergence rate in this part of the Himalayas is about 18 mm per year which has continued for more than 500 years — making this slice of the geological fault “one of the most earthquake-vulnerable segments of the Himalayan arc.” 

The network of GPS sites in the Garhwal Himalayas, the densest anywhere along the Himalayan arc, “provides the most reliable estimate of spatial variations of site velocities in the Himalayas,” the authors say. – IANS