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The science of predicting an earthquake

The science of predicting an earthquake
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First Published: Mon, Nov 16 2009. 01 15 AM IST

Precursor watch: Researcher Naresh Kumar adjusting a gravimeter. Ramesh Pathania / Mint
Precursor watch: Researcher Naresh Kumar adjusting a gravimeter. Ramesh Pathania / Mint
Updated: Sun, Aug 08 2010. 01 34 PM IST
Ghuttu, Uttarakhand: Perched at an altitude of 6,000ft, among the scenic peaks of the Lower Himalayas and the verdant Bhilganga Valley, a group of mild-mannered scientists are pottering around their instruments, eagerly awaiting the next big earthquake.
Precursor watch: Researcher Naresh Kumar adjusting a gravimeter. Ramesh Pathania / Mint
“At least a 6 (in magnitude) and within a 200km radius,” says Naresh Kumar, a researcher in his mid-30s, with the Wadia Institute of Himalayan Geology (WIHG) in Dehradun. Since 2007, Kumar has been shuttling between his workstation in Dehradun and Ghuttu, a charming hamlet 200 rubbled-and-winding kilometres away.
Unknown to even most of its local population, Ghuttu hosts India’s first coordinated attempt at studying earthquake precursors—or warning signals to a coming earthquake. The laboratory, called the Multiparametric Geophysical Observatory, atop an isolated hill, is much more than the six white rooms spread across an area slightly more than half a hockey field.
Each of these cramped quarters hosts instruments such as gravimeters, essentially ultrasensitive weighing machines, and specialized magnetometers that measure minute changes in the gravitational force, the ups and downs of the magnetic field surrounding the rocks within a 50km radius, as well as continuously survey the radioactivity of the water table in the vicinity.
There are the workhorse seismometers, too, which have long helped scientists pinpoint the intensity and location of an earthquake. But these other instruments, which continuously stream data via a VSAT satellite connection to Dehradun, are helping these scientists create an electromagnetic profile of the rock structure in these parts.
“In another decade, we should be able to quantify whether we can record earthquake precursors of earthquakes of magnitude 5 and above,” says Baldev Arora, former director, WIHG, and credited with setting up the laboratory.
Since the 1970s, scientists internationally have been mapping prominent earthquake-prone zones such as the San Andreas Fault, which runs across California, for unusual electromagnetic signals, or structural fissures and strains in the rock patterns. Such signals are a sign that pressure, or vast reserves of heat and radiation, are bubbling up over time between tectonic plates that are continually moving and at various times may collide, diverge or slide against one another.
These energy vents begin to disturb the rocks that lie on these plates and leave a variety of signatures that are picked up by magnetometers or gravimeters.
Current theories say that the Indian land mass, which rests on a plate called the Indo-Australian Plate, is sliding along another massive structure called the Asian Plate, which includes China and Japan.
The ensuing energy release from this friction not only created the Himalayas, but also spread along a line called the Main Central Thrust (MCT), a 2,500km long zone that stretches from Bhutan to well beyond India’s western border. This line hosts several tectonic rocks, ones that are perched along one another and by virtue of their unsteady nature are subject to changing gravitational pulls and pressure, that are most likely to trigger earthquakes.
Even though India doesn’t see as many significant earthquakes as parts of the US or Japan, it has lost several thousand lives to earthquakes in the 20th century.
Though the most vivid earthquakes in India’s memory may be the Bhuj earthquake of January 2001 in Gujarat and the Latur earthquake of September 1993 in Maharashtra, experts say that historically quakes are far more frequent in northern and north-eastern India. The government’s latest seismic zoning maps list Uttarakhand, Sikkim, Himachal Pradesh, Bihar and parts of Delhi as category 4 and 5—making them the most earthquake-prone regions in the country.
“In putting up a centre over here, we’ve made a balanced, well-thought-out gamble,” says Arora. That’s because India’s biggest earthquakes in the last century, such as the Kangra quake (7.5 magnitude) in 1905, and the Bihar quakes in 1934 (8.6 magnitude) and 1950, were all along different points in MCT. Given the volatility of MCT, a big earthquake—of at least 6.5 magnitude—within a 50km radius of Ghuttu is imminent. “This region has not seen a big one in 200 years. So it’s only a matter of time,” Arora emphasized, without specifying a time frame.
Apart from Ghuttu’s coordinates—it is a mere 5km off the MCT fault line—what worked in its favour was the abundance of so-called hard rock, which makes it easier to record shifts in gravity and the magnetic fields, as well as its relative isolation from human settlements.
“In Srinagar, when we were testing some of these instruments, most of the readings on the instruments were from people kick-starting their scooters,” says Arora.
Recent significant earthquakes such as the 1991 Uttarkashi and 1999 Chamoli earthquakes are located around MCT, but were of less than 7 magnitude.
The vagaries of gravity and magnetic fields apart, scientists here are also looking at the concentration of radon gas—a by-product of uranium decay—in the water table as an earthquake precursor. The metric has gained importance ever since Chinese scientists included such data to accurately predict the 1975 earthquake in Haicheng, China.
However, the scientists at Ghuttu are yet to sense success. The researchers add that a “small” earthquake, 60km away, that touched 5 on the Richter scale didn’t generate any unusual early warning signals on the gravimeter that weighs about a tonne and boasts an ultrasensitive niobium sensor bathed in super-cooled liquid helium, and that is even sensitive to footsteps.
Still, “there were changes during the earthquake, but the magnetic fields and the radon did show some unusual readings a few days before”, says B.I. Khandelwal, another scientist who does 20-day stints atop the lonely hillock, “at least once in two months”.
The researcher, who is responsible for everything from taking readings twice a day on the magnetometers to ensuring a steady power supply for the gravimeter, says he is used to the solitude and the silences.
“It does get boring, because the newspapers don’t come here. But now it’s much better,” he says. The comfort comes from power cuts lasting a “mere” 6 hours compared with outages lasting as long as 7-15 days at a time earlier. Also, the newly installed Airtel tower nearby means he can have uninterrupted conversations with his family instead of climbing the nearby water tank and banking on stray, ephemeral signal.
But the occasional leopard is still a worry. “I never leave this place without a bat,” Khandelwal says of his occasional nightly trips to the village for provisions and newspapers.
Despite several instruments and rigorous monitoring, most earthquake precursors are still iffy.
“In 1976, the very next year (after the Haicheng quake), the Chinese completely missed a huge quake, and the radon levels were normal. Similarly, the San Andreas Fault was to throw a major quake in the early 1990s, but all that we got was a 5 magnitude one—that too 11 years later. So, nature always surprises us,” says Arora.
jacob.k@livemint.com
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First Published: Mon, Nov 16 2009. 01 15 AM IST