Geological factors

WHEN Dr. P.P. Patel, Professor and Head of the Department of Geology at M.S. University, Baroda, felt the tremors on the morning of January 26, his professional instincts told him that an earthquake with Bhuj, Bhavnagar or the Narmada Valley as the epice ntre had occurred.

An engineering-, environmental- and hydro-geologist who has intimate knowledge of the Kutch region, Patel emphasised the fact that the earthquake could have been foreseen. "On December 27 there was an indication of heightened seismic activity. A minor e arthquake measuring around 4 on the Richter scale occurred in Bhuj. It was ignored - it appeared as a small report in a Gujarati newspaper." Fearing renewed seismic activity, Patel organised a field workshop at the Bhuj Observatory in collaboration with the local administration and the Department of Science and Technology.

Patel believes that the government should step up geological and structural mapping of the area. He says: "We have the base maps of the region done about a century ago by the Geological Survey of India. They provide excellent data. We need to superimpose the new data and identify possible problem areas." Patel believes that such monitoring could have assisted in making a prediction to a high degree of accuracy.

The surface of the earth consists of seven major moving tectonic plates. The plates directly relevant to India are the African, Arabian, Eurasian and Indian plates. The Bhuj earthquake was an intraplate earthquake caused by the slow-motion collision of m oving plates.

Although in geological terms Kutch is young, being only 200 million years old, it is only a little older than the Himalayan region. As in the case of the Himalayas, the geological stresses of the region are still unstable. Patel explains: "The blocks of rock under the earth's crust are always under great stress. There is continuous pulling and pushing and magma activity. Sometimes, when this goes beyond the stress capability of the crust, the stored energy shoots out and the ensuing vibrations cause an earthquake."

Between 1845 and 1956 Kutch experienced 66 moderate earthquakes in which no loss of life was reported, five severe earthquakes and one very severe quake on June 19, 1845 in which the northern town of Lakhpat was ruined. In that instance, 66 shocks were c ounted over a week.

The really big one for the region was that of June 6, 1819 that shaped Kutch's future. The region's desert-like conditions owe their origin to that earthquake, which killed 2,000 people and threw up a 100 km ridge and created what is known as the Allah B und, now in Sind. The bund effectively diverted the course of the Sindhu river, which till then used to flow into Kutch. The magnitude of the 1819 quake was an estimated 7.7 on the Richter scale.

Kutch district occupies 50,000 square km. The tectonic distribution and structural geology of the region is such that it forms one geological unit called the Kutch basin. There are, however, connecting faults that link the regions. A 200-km long and 100- km wide trench with an east-west orientation runs from Bhuj to Ahmedabad. Another trench, a more gigantic one, called the Cambay Grabon, is 500 km long and 100 km wide and cuts in a north-south direction through central Gujarat running through the region s of Ahmedabad, Mehsana and Baroda. These subterranean trenches intersect near the towns of Viramgam, Santhalpur and Radhanpur, all steadily growing commercial centres.

Adding to the potential volatility of the region is the presence of numerous hot water aquifers. Located a mere 500 m below the surface, these are heated by magma. These aquifers are tapped by hundreds of tubewells, and the water that gushes to the surfa ce flows under artesian force and is boiling hot.

Fears that human activity could be aggravating seismic activity are put to rest in the case of this earthquake, though Patel agrees that the heavy extraction of groundwater and oil and the construction of big dams would definitely tend to aggravate tecto nic activity.