The Telegraph
Since 1st March, 1999
Email This Page
Quake cell cocks ears for big one

New Delhi, Oct. 15: Along the 2,400-km stretch of the Himalayas, geophysicist Harsh Gupta hopes to once again attempt a feat in earthquake forecasting that he had achieved in India’s Northeast two decades ago.

Gupta, a scientist at the National Geophysical Research Institute (NGRI), Hyderabad, heads a panel of experts now pencilling a plan to intensify the search for early warning signals, or precursors, for earthquakes.

The discovery of reliable precursors is expected to help governments and people become better prepared for the “big one” that scientists believe is yet to strike somewhere in the Himalayas.

The search for precursors, backed by the department of science and technology (DST), comes at a time when scientists are sharply split over whether earthquakes are predictable. Some geophysicists argue that the underground processes that lead to catastrophic lurches in the earth’s crust are too complex for forecasts.

“But earthquake prediction is still a young science ' just about 30 years old. We need time,” says Gupta. It was only in the 1960s that geophysicists connected earthquakes to the shifting of continental plates and developed a credible earthquake science.

Gupta says a technique that uses seismic signatures called “swarms and quiescences” had led him to a successful medium-term forecast in the Northeast.

Swarms are a large number of relatively weak earthquakes that occur in quick succession in a small region ' sometimes between 15 to 20 in a year. Quiescences are quiet periods ' perhaps less than five earthquakes a year.

The concept of using swarms as precursors emerged from scientists at the University of Wellington in New Zealand during the 1970s.

In 1986, Gupta, who was then NGRI director, studied swarms and quiescences associated with 12 earthquakes in the Northeast over the previous several decades. He forecast that an earthquake between magnitude 7.5 and 8.5 would occur somewhere in an area of 300 km by 450 km, stretching across parts of Assam, Manipur and Mizoram, before the end of 1990.

A 7.5-magnitude earthquake did occur within the earmarked zone on August 6, 1988. Some scientists argue that the prediction was not a genuinely “helpful forecast” for it covered too wide an area and too long a forecast period ' four years.

But Gupta says that once such broad zones of likely earthquakes are identified along the entire Himalayas, scientists will use other precursors, such as changes in the ground characteristics, to shrink the area of uncertainty. “There could be changes in magnetism or gas emissions from the ground or even temperature changes.”

“I think doors should be open for all lines of research,” says Dr C.P. Rajendran, a senior scientist at the Centre for Earth Science Studies in Thiruvananthapuram. “Prediction to study ground motion would also help forecast the impact on structures.”

“If the swarm-and-quiescence technique worked in the Northeast, it’s worth pursuing along the rest of the Himalayan belt, too,” says Kamal, the head of geophysics at the Wadia Institute of Himalayan Geology, Dehra Dun.

Under a DST initiative, several institutions are installing seismic instruments along the Himalayas to improve the data-gathering network.

“We’ll need years of data to recognise swarms and quiescences,” Kamal said.

Four years ago, a research paper by University of Colorado’s Roger Bilham and Indian geophysicist Vinod Gaur had warned that the Himalayas appear ready for a powerful earthquake, a bigger killer than all earthquakes in India over the past 200 years.

Gupta says efforts to protect vulnerable buildings should begin now and not wait for the discovery of precursors.

A few weeks ago, Gupta was advising authorities in Uttaranchal on techniques to protect houses in the hills.

Email This Page