Rocking the Himalayas

14/01/1995
Down To Earth

Rocking the Himalayas MASSIVE quake to hit northern India, screamed a headline in a national daily on December 20, 1994. After being stumped by the Latur quake of 1993, Indian geophysicists are back to their obsession with the mysteries that the 3,000-km long Himalayan belt holds under its awesome heights. The latest shockwave has its epicentre in the predictions of an imminent earthquake levelled by Roger Bilham of the University of Colorado, Boulder, USA.

Recovering from the initial tremor, Indian scientists have professed doubts about the very methodology of the predictions, which is the soft underbelly of earth sciences. The "warning", however, has led to the clearance of plans by the government for carbon dating geostrata in northern India to study any seismic activity that might have occurred in the area over aeons. Although doubts have been raised over the authenticity of the prediction, the Union ministry of agriculture (MOA) is taking no chances and is busy formulating a contingency plan in collaboration with other agencies.

At a meeting of the American Geophysical Union in San Francisco on December 9 last year, Bilham presented seismic data indicating an imminent earthquake in the central Himalayas. He combined historical data catalogued by Richard Dixon Oldham, director of the Geological Survey of India (GSI) from 1850-76, and the latest satellite technology. And then he punched the alarm button.

Sticking to his "doomsday prophecy", Bilham told Down To Earth, "Its like a sword of Damocles hanging over northern India. A massive earthquake could hit the central Himalayan region of India anytime. The quake could be of the magnitude of 8-9 on the Richter scale and could devastate a region inhabited by 200 million people."

Bilham has found a supporter in Vinod Gaur, former director general of the National Geophysical Research Institute (NGRI). According to Gaur, now based at the Centre for Mathematical Modelling and Computer Simulation at Bangalore, "The prediction is result of the first ever direct measurement of the Indian plate's movements in relation to Asia. The Himalayas were raised when the north-moving Indian sub-continent rammed into the Asian mainland about 40 to 50 million years ago. It continues to move northwards at a speed of 2 centimetre per year, about the same velocity as the notorious San Andreas plates."

A playground for quakes This movement has made the Himalayas a playground for earthquakes. Bilham, using the Global Positioning System (GPS), a network of satellites and ground stations, to chart the progress of set of points on the Indian tectonic plate between 1991 and 1994, claims to have found the exact measurements. According to Bilham the GPS data indicates that, along the Indo-Nepal border, the margins of the 2 major plates have got stuck and instead of sliding smoothly, they are "flexing". "The flexing is leading to the storing of immense amounts of energy. An earthquake could result when the plate margins finally slip to release the energy. The intensity of the quake will depend on how much stress has been accumulated along the plate boundary," he maintains.

Bilham warns that the stress might be reaching a critical point in Northern India if the historical data is accepted as evidence. Says he, "If the Indian plate has been moving at a speed of 2 cm a year, about 6 to 13 metres of slip has accumulated over the past 700 years. It cannot exceed 13 metres because that exceeds the rupture strength of materials."

Leading Indian seismologists, however, do not entirely agree with Bilham. V P Kamble, additional director general (seismology), the Indian Meteorological Department (IMD), says, "Seismology is a complex subject involving activity 15-20 km below the earth's surface. The per day accumulation of strain cannot be charted; nor can creek movements be carried out with any precision. Thus, predictions cannot be made the way it has been done." However, K S Valdiya, an expert on neotectonics (the study of current plate movements), says, "The Himalayas are an extremely restless mountain range. Threat of major tectonic upheavals is real as the range is under immense tectonic stress."
Historical data unreliable The use of historical data by Bilham has also been challenged. Says Kamble, "Past data is insufficient and unreliable. Meticulous documentation of seismic data started only in 1950s." Adds A S Arya, professor emeritus at the Roorkee Earthquake Engineering Department, "Historical data is not foolproof. For instance, in 1803, the Kumaoun in the Himalayas and Calcutta were hit by quakes within a span of 2 days. Historical records might show them as the result of same upheaval, which might be incorrect. What happened in the Gangetic plain might not be true for the mountains."

Tectonic upheavals have split the 3,000 km span of the Himalayas into 3 segments, creating space gaps. The western fringe (north of Delhi) broke in 1905 during the Kangra earthquake. Two earthquakes in Bihar and Assam in 1934 and 1950 broke the eastern fringe. The unbroken central segment is now locked between the 2 fringes. But Kamble argues, "Although there has been considerable tectonic activity in the region, whether they are precursors to a major earthquake is something nobody can clearly predict. Foreshocks or increase in frequency can provide an early warning, but only if we are lucky."

The Indian earth scientists seem to be partially agreeing with the arguments and results floated by Bilham. Ramesh Chandra says, "The data collected by the IMD and the GSI and preliminary calculations based on ground elevation changes suggest that permanent deformation as well as earthquake generating stress has been accumulating in the region. But when an earthquake will strike cannot be predicted with certainty."

There are other objections to Bilham's study. Argues Arya, "Even if the stress building up along the Indo-Nepal border results in a quake, it cannot be stated with emphasis that the dams or such and such area will be affected. This is dependent on where the earthquake occurs. The damage will be vastly different if the epicentre is under a dam or 300 km away from it." Adds Ramesh Chandra, "The acceleration due to quakes have a tendency to die down by 50 per cent after travelling some 50 odd kilometres. Thus, summary claims of a quake affecting 200 million people are exaggerated." A senior NGRI geophysicist contends, "The Himalayan region is replete with fault lines. The energy released during a quake is not concentrated to a particular area and its spread is difficult to ascertain."

Arya, one of the foremost structural engineers of the country, however, warns that if an earthquake occurs, the damage might be extensive within a radius of 70 to 80 km, creating another Uttarakashi. "The problem is not with the dams but the stone and mud structures that dot the hills and the poorly constructed houses in the foothills. None of the basic elements of earthquake resistance is incorporated in their construction," he maintains.

The warnings from Colorado have generated significant response as eyes remain riveted on the central Himalayas. Meanwhile, the MOA has created an elaborate contingency programme in case of a quake. What is bothering many is that the warning came from as far as Colorado. Its being argued that if seismic activity is so intense in the region, why weren't steps being initiated to cushion the impact.

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