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Journalism of Courage
HYDERABAD, JAN 28: The Bhuj earthquake unleashed energy equivalent to a 5.3 mega tonne Hydrogen bomb and the aftershocks of this violent force will last for months, director of the National Geophysical Research Institute (NGRI) has said.
Harsh Gupta told PTI that his laboratory recorded at 6.34 am today an aftershock measuring about 5.9 on Richter scale, the largest since the main earthquake devastated the Kutch town last Friday.
NGRI has so far recorded seven aftershocks above the magnitude of 5 but, Gupta said, there is no way of telling when the region will become quiet again. “Considering that the main quake measured about 7 on the Richter scale, it can take months,” he said. Aftershocks arise not from the original fault but from segments in the neighbourhood.
NGRI, one of the institutes under the Council of Scientific and Industrial Research (CSIR), has made extensive studies of all major earthquakes that had rocked the country.
Gupta has advised residents of earthquake-affected towns to stay away from their homes, especially if the houses had developed cracks. He added that CSIR is proposing to send building research experts to Gujarat for inspection of structures that are still standing and suggesting remedial action.
According to Gupta, the only way to prevent deaths from earthquakes is to make it mandatory for builders to abide by the building codes provided by the Indian Bureau of Standards for structures in the five different seismic zones of India. These codes are revised every five years, “but the trouble is that contractors are not aware of these,” he added.
Gupta said that in rural India, where people live in non-engineered structures, all that may be required is to place two cross-strips of steel on each wall and reduce weight on housetops.
Gupta added that a global map is already available, showing the earthquake hazard potential of every place on earth. “What we now have to do is to convert the hazards potential into risk potential by taking into account the local factors.”
He said NGRI is doing this for Jabalpur, with support from the Department of Science and Technology (DST), and it will start similar work in 12 more quake-prone cities once the DST approves the proposal.
On the controversy over the magnitude of the Bhuj quake, he said the value depended on whether one used the body wave (which penetrates the earth) or the surface wave (that travels on the surface) analysis.
The American geological survey value of 7.9 was based on surface wave calculation of global data from 86 stations while Indian meteorologists used body wave analysis of data from 10 stations, giving the value of 6.9.
Gupta pointed out that the magnitude of a quake is not the same as its intensity. The latter depends on local geology, meaning that a quake of a given magnitude can cause more damage in one place and less in another place.
