India's Himalayan Region is highly vulnerable to earthquakes and according to an estimate by the World Bank, in a year, about 1000 small and big earthquakes strike the country.
The National Disaster Management Authority (NDMA) in an assessment found that almost 59 per cent of India is "vulnerable to moderate or severe seismic hazard".
Startlingly it also found that most buildings in sub-urban areas are "non-engineered and built without adhering to earthquake resistant construction principles… Traditional houses are being replaced with modern reinforced cement concrete (RCC) buildings, often without compliance to building codes and bye-laws".
The NDMA reports that between 1990 and 2006 India has experienced six major earthquakes that have resulted in deaths of over 23,000 people and caused enormous loss to infrastructure.
The NDMA echoes an ominous warning that "very severe earthquakes are likely to occur anytime in the Himalayan region, which could adversely affect the lives of several million people". But a complacent government and civil society do not seem to care much about these forewarnings.
"A time bomb is ticking. It is not a question (of) if, but when the big great earthquake of over 8 magnitude will strike northern India," asserted C P Rajendran, a paleo-seismologist at the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Bengaluru.
His concerns were echoed by Harsh Gupta, a hugely respected seismologist and former secretary of the Ministry of Earth Sciences, who says "in a way yes there is a ticking bomb because a great earthquake in Himalayan region is overdue it could occur anytime."
Since predicting earthquakes is nearly impossible, scientists try to study the past records to try decipher some clues for future forecasting.
According to a recent report by the JNCASR, the central part of the Himalaya is noted for its frequent earthquakes. It becomes crucial to study past earthquakes to understand the pattern of recurrence—how frequently the earthquakes occur, under what conditions. The area also contains many natural limestone caves, which act as sites that preserve imprints of major earthquake events in the area.
"The caves the scientists studied are located close to these faults will also be disturbed because of the ground movements," Rajendran explains.
"We chose some caves because they were located between two major Himalayan thrusts [faults]: Main Central Thrust (MCT) and Main Boundary Thrust (MBT). So any major ground shaking associated with earthquake activities linked to these structures will possibly be recorded within the cave in the form of growth anomalies," Rajendran adds.
The central Indian Himalayas have many natural limestone caves, where water from the roof causes two types of formations to occur.
Stalactites are pillars of calcium salts that hang from the roof, and stalagmites, again made of calcium, grow up from the floor of the caves, says the report.
"The caves get tilted due to earthquakes, and cave formations like stalagmites have to readjust their growth trajectories. These changes can be understood from the tilt angles preserved in the body of stalagmites. Another kind of damage expected is related to collapse of cave roofs due to earthquake shaking," explains Rajendran.
The width and length of the stalagmite depend on the drip water, the size of the droplet and the distance from the ceiling. Each layer preserved within the stalagmite often acts as a repository of its growth history—something like tree bands that allow us insight into the past.
Each growth band can be dated precisely, explains Rajendran. "Moreover, as many are long lived, for thousands of years, it can give a long-term history of their growth. Both climatic and tectonic signals can be ideally deciphered from them. Deviations from the systematic growth is expected to reflect the ground tilting due to big earthquakes," he says.
The study of stalagmites gives a tool to go back much deeper into past and in conjunction with geological and geophysical data help us expand databases on earthquake hazard of the Himalayan region reports Rajendran.
Another reason why temblors of high magnitude are expected in northern India is because of the rather unique and peculiar geological history of India. According to the well accepted theory of plate tectonics which explains the movement over eons of the continental plates all floating on an ocean of molten magma in the core of the Earth.
As a consequence, some 71 million years ago the Indian sub-continent actually started drifting away from Africa moving northwards later it came and collided with the huge Asian landmass. Since then the Indian plate is constantly being pushed under the Asian plate at the rate of about 5 cm every year.
This jostling builds up a huge strain deep within the earth starting in a large, almost 2400 kilometre swath stretching from Afghanistan to Arunachal Pradesh. When this inherent but latent pressure built due to the tectonic wrestling is released, we sense it as earthquakes.
The young and restless Himalayas that are still rising annually by about 5 millimetres epitomize and literally showcase the danger that is hidden and building up deep within the womb of Earth.
Gupta says "there is a definite possibility of the great earthquake, of magnitude 8 in the Himalayan region, there is no doubt about it…When it will happen, no one can guess, where it will happen, is also a big question mark."
Each of these earthquakes results from what seismologists call a big rupture that occurs in the crust of the earth, literally a deep shearing of the plates as they rub against each other on the fault line and the pent up stress is released in the form of energy that causes the jolts.
According to an estimate published in American journal Science by leading Indian seismologist Vinod K Gaur at the Indian Institute of Astrophysics, such great earthquakes have a revisit time of almost 500 years.
Roger Bilham, a top seismologist from the Department of Geological Sciences, University of Colorado in Boulder, USA, says "more important today, is that less than half of the Himalayas has ruptured" which essentially means the strain is building every day which will be released at some point soon causing a massive temblor.
According to Bilham, one region where the stress has not been relieved for the last almost 600 years is the Himalayan fault almost north of Delhi, the last big earthquake to have been recorded from this hot spot was way back in 1505.
Extrapolating based on past fatalities caused due to historical earthquakes like the 8 magnitude earthquake that struck Kangra in 1905 and then factoring in for on the increased population densities, Bilham estimates "200,000 predictable fatalities" if a big one strikes now.
The World Bank has recently embarked on a month long 10,000-kilometre road journey along India's coast called 'Road to Resilience' which will end in Bhuj, the city that was devastated by a 7.7 magnitude earthquake 15 years ago on the morning of the R-Day in 2001 which killed over 12,000 people.
Saurabh Dani, senior disaster management specialist at the World Bank, Washington DC, USA says "India can do a lot more towards reducing the risk due to earthquakes."
The 'big one' is really waiting to happen just that we don't know where and when. Experts say the only way to diffuse the time bomb is to build safe. So the message is that, if the past is the key to the present, a real big one is expected in the central Himalaya segment. Therefore get prepared," warns Rajendran. The old learning holds true "earthquakes don't kill it is really unsafe buildings that kill".