GSI project to document earthquake-induced landslides in India, understand process triggering such incidents

Vijay Mohan

Chandigarh, June 14

The Geological Survey of India (GSI) has initiated a pioneering project to compile an inventory for earthquake-induced landslides and understand the underlying factors causing such landslides.

An atlas of earthquake-induced landslide susceptibility will also be published.

Large parts of the country are seismically vulnerable and prone to earthquakes, which have triggered landslides in many places. Such events have taken a heavy toll on life and property as well as caused environmental damage.

Under a two-year project, an area of about 1,000 square kilometres around Nako in north-eastern Himachal Pradesh will be surveyed, according to GSI sources. The area falls under Zone 5 of the seismic zonation map of India, which is the most vulnerable.

According to GSI officials, predicting the place and conditions under which earthquakes are likely to trigger landslides are key elements in regional seismic hazard assessment. Susceptibility assessment is critical for prevention and reduction of such incidents as well as for disaster management and reconstruction in affected areas.

An earthquake magnitude of greater than 4 and intensity of VI is required for generation of an earthquake-induced landslide. The mechanism of triggering such landslides is complex and is an active ongoing research subject.

When an earthquake occurs, the transmission of seismic waves can cause shaking and vibration of the ground surface, which can trigger the collapse of unstable or geologically weak slopes, causing a landslide.

Several factors affect the scale of landslides, such as the nature of earthquakes and geographical, hydrological and meteorological conditions of the area. Earthquake-induced landslides are huge in size, distributed widely and can be detected even after hundreds of years after their occurrence, according to geologists.

The 1994 earthquake in California is the first case for which a rigorous regional analysis of seismic slope instability was conducted, but in India no such attempt to study disastrous earthquakes has been made so far, according to GSI officials.

About 15 per cent of India’s landmass is vulnerable to landslides of varying degrees. According to the Landslide Atlas of India released by Indian Space Research Organisation (ISRO) earlier this year, the Northwest Himalayas contribute 66.5 per cent of landslides in India, with the Northeast Himalayas and the Western Ghats accounting for 18.8 per cent and 14.7 percent, respectively.