Contrary to the general perception that the entire North East region faced high seismic hazard, a new finding based on GPS measurements has shown that the risk of a major earthquake was low in that area, particularly in Manipur, Nagaland and Mizoram.
“It is a new discovery. We have sort of lowered the risk,” observed Dr.Vineet Gahalaut, who is heading the team of GPS group at National Geophysical Research Institute (NGRI), which is studying seismic activity across different regions in the country. Using GPS measurements, the seismologists found that in North East India the relative plate motion between Indian and Sunda plates occurred along a fault named as Churachandpur Mao Fault.
However, it was not experiencing strain build-up due to slippage on a continuous basis. As a result, the possibility of occurrence of a major or great earthquake in the Indo-Burmese arc was very low, he said.
The contrast In the Kashmir Himalayan region, the strain build-up was high and the release of the accumulated stress could result in a major or great earthquake in the future. While the rate of strain accumulation in Nepal was two cm/ year, it was 1.4 cm/ year in Kashmir.
Dr. Gahalaut said that another fault known as Karakoram fault in Ladakh accommodated some of the relative plate motion and hence the strain build up rate in Kashmir was not as high as that in Nepal region. “Although, it was felt earlier that there was no connection between Karakoram fault and tectonic movement in the Himalayas, we find there is a link and part of the stress caused by the plate motion is accumulated there,” he said.
Right from Kashmir to Nepal, there was a risk for major earthquake because of the strain accumulation.
Another interesting finding related to infrequent occurrence of earthquakes in peninsular India. The seismologists found a distinct difference in the earthquake occurrence and deformation processes in plate interior regions as compared to plate boundary regions.
Migrating with time
According to Dr. Gahalaut, the deformation or seismic activity in interior areas was quite localised and occurred in small pockets. However, the deformation keeps migrating with time over tens of hundreds of years. For instance, Bhadrachalam in Andhra Pradesh, which experienced a moderate earthquake in 1969 does not show any deformation now.
He said the deformation had shifted elsewhere along the Godavari Basin (Godavari failed rift region) which might witness an earthquake in future. “But the deformation is very localised and this is a major breakthrough in our understanding.” He, however, warned that even a moderate earthquake in peninsular India could kill more people than a big temblor in the Himalayas because of high population density.
