NCR’s low-intensity tremors worrisome

Sushil Manav

Tribune News Service

Chandigarh, June 19

A series of low-magnitude tremors witnessed in the NCR indicate that the fault line in the region has become unstable. However, low-magnitude tremors rocking the NCR twice in two days with Rohtak as the epicentre may not be enough to conclude that a bigger earthquake is in the offing in the near future.

A low-intensity earthquake measuring 2.3 on the Richter scale hit an area 15 km east-southeast of Rohtak on Friday morning, according to the National Centre for Seismology.

‘FAULT LINE UNSTABLE’

A number of tremors during the past few weeks indicate that the fault line in the NCR has become unstable. Although the Aravalli ridge, which covers quite a large area of the NCR in the south, is considered relatively stable, the increasing frequency of tremors is a cause of concern as it may be an indicator of moderate-intensity earthquakes in the future. —Dr Mahabir Jaglan, Professor, Kurukshetra University

This was the second consecutive earthquake near Rohtak. An earthquake measuring 2.1 on the Richter scale occurred at 4.18 am on Thursday.

Several low-intensity earthquakes have been hitting the Capital and surrounding region since April. On May 29, an earthquake measuring 4.6 on the Richter scale, with a depth of 3.3 km, had its epicentre 16 km east-southeast of Rohtak.

Seismologists say a bigger earthquake is generally preceded by multiple earthquakes of lower magnitude. Prof Dinesh Kumar, noted seismologist and head of geophysics department at Kurukshetra University, said there were two theories the world over in this regard.

He said according to one theory, major earthquakes were preceded by multiple tremors of low intensity. He said according to the other, there could be a quiet period, with no seismic activity for a considerable time, before a major earthquake.

Professor Kumar had worked on earthquakes in the NCR and was credited with the study “Evaluating the seismic hazard to the National Capital (Delhi) Region, India, from moderate earthquakes using simulated accelerograms”.

“The NCR lies in the geographical realm of peninsular India (PI) and is about 200 km from the Indian plate boundary (Himalayas). Traditionally, PI has been considered seismically stable. However, recent occurrences of several hazardous events within the PI, such as the 1967 Koyna, 1993 Killari, 1997 Jabalpur and 2001 Bhuj earthquakes, have prompted scientists and planners to reconsider the unrealistic assessment of seismic hazard and risk to the region,” he said.

He said the NCR was exposed to earthquake hazards and risks in two scenarios — a great earthquake in the central seismic gap of the Himalayas or a moderate earthquake within the NCR.

Dr Mahabir Jaglan, professor in geography at Kurukshetra University, said the NCR lied in Seismic Zone 4 and hence, was vulnerable to low to moderate earthquakes.

“A number of tremors during the past few weeks indicate that the fault line in the NCR has become unstable. Although the Aravalli ridge, which covers quite a large area of the NCR in the south, is considered relatively stable, the increasing frequency of tremors is a cause of concern as it may be an indicator of moderate-intensity earthquakes in the future,” he said.

He said the mushrooming of high-rise buildings in Noida, Gurugram and Delhi and construction of skyscrapers in violation of the building code and Bureau of Indian Standards norms had increased the vulnerability of the NCR to earthquakes.