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Scientist finds similarities in Ahmedabad, Mexico City quakes

There are several similarities between the Republic Day earthquake in Ahmedabad and the killer earthquake that hit Mexico in 1985, a scientist has said.

As in the case of the Mexico quake, soft soil fillings may be one of the causes for the massive devastation that resulted from last week's earthquake in Ahmedabad, said Professor Vinay Kumar Gupta of the Indian Institute of Technology, Kanpur.

Prof Gupta said reports from the commercial capital of quake-ravaged Gujarat indicated certain similarities in the pattern of damages and reasons for the earthquake.

He said it was surprising that places like Ahmedabad, which were about 300km away from the epicentre of the quake, had suffered so much devastation.

Gupta said he was told that earlier Ahmedabad and its surrounding areas had a number of ponds and waterholes, which were buried under soft soil fillings in course of time. Several new colonies had come up on these lands. This phenomenon coupled with the 'poor quality' of construction work and suspected violation of the seismic code might be the cause of the massive loss of life and property witnessed last week, he said.

Mexico City is also founded on soft fillings of volcanic deposits. It too was located about 400km from the epicentre of the deadly earthquake that hit Mexico in 1985, yet buildings with 10 or more storeys and other structures had suffered maximum damage.

He said friends in Ahmedabad had told him that three- to four-storeyed buildings in various new colonies of the city had suffered maximum damage while localities in Old Ahmedabad witnessed less devastation.

Elaborating, Prof Gupta said soft soil fillings facilitate amplification of the motion of seismic waves. In a situation where the natural period of the soft filling and the structures on it is equal, the devastation is maximum.

The scientist said the veracity of his observations could be ascertained if the seismic motion is monitored at various locations in Ahmedabad. This can be done even now as aftershocks are occurring.

He said variation in the motion at different locations would be a confirmation of his observation. Accordingly, the practice of sub-seismic zoning and micro-seismic mapping and enforcement of seismic code could minimise the extent of devastation in situations like those in Mexico and Ahmedabad, he added.

UNI

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