40 micro quakes shook Dahanu in 24 hours; tectonic, not artificial: Experts

Written by Srinath Rao , Gargi Verma

Mumbai | February 5, 2019 03:29 AM IST

4 min read

40 micro quakes shook Dahanu in 24 hours; tectonic, not artificial: Experts

According to the experts, who briefed officials of the State Disaster Management Authority, the tremors, known as “swarm earthquakes” because of their frequency and concentration in a small area, were caused by the movement of tectonic plates which is normal in the Indian peninsula.

FORTY MICRO earthquakes shook Dahanu taluka in 24 hours between February 1 and 2, seismologists studying a series of tremors in the area since the last three months have found. The tremors were recorded in an area of 18 square kilometres and picked up by seismographs installed in five locations in Maharashtra’s Palghar district, in which Dahanu is located, since November 2018.

“We studied 40 micro earthquakes between February 1 and 2 and found that they are tectonic in nature. They are not artificially created as there are no major reservoirs in the area. Most of these earthquakes were so minor that it is unlikely that people felt them, but they were picked up by our machines,” said Dr Srinagesh D, who heads the Seismological Observatory at the National Geophysical Research Institute, Hyderabad.

With more than 10,000 panicked residents of 40 villages in Dhundalwadi grampanchayat having fled their homes and camped outdoors since the tremors began on November 11, 2018, the state government had asked the NGRI to present its findings on Monday. According to the experts, who briefed officials of the State Disaster Management Authority, the tremors, known as “swarm earthquakes” because of their frequency and concentration in a small area, were caused by the movement of tectonic plates which is normal in the Indian peninsula.

Both the NGRI and the National Centre for Seismology, Delhi, have set up five stations in the district equipped with seismographs to measure velocity, and accelerometers to study the quakes and intensity with which the ground shakes. “We have isolated the source to an area 10 square kilometres in length and 5 square kilometres in breadth. Over the next one month, we will be trying to find the exact source,” he said.

He also informed the State Disaster Management Authority on Monday that no new tremors were reported in the last 24 hours by locals in Dhundalwadi, where homes have developed cracks and walls have collapsed. The sense of panic has also been exacerbated by the death last week of a two-year-old girl who fell while fleeing her home with her family.

Prashant Narnavare, Palghar district Collector, said that families have been encouraged to evacuate their homes.

Dr Srinagesh conceded, however, that a lot more data needs to be collected, adding that it was too early to tell whether the earthquakes were migrating. Over the last three months, the scientists had also investigated whether the quakes were being caused due to hydro-seismicity – the percolation of rainwater post-monsoon – or magmatic activity.

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Swarm earthquakes are also known to have lasted much longer, with tremors shaking Vellore in Tamil Nadu for 287 consecutive days in 2016-17. “The locals were afraid but did not panic as they remembered that the ground had shaken much more during Latur 1993,” he said.

On the basis of the 48-hour observation, Dr Srinagesh said the data points to the earthquakes being tectonic, like 99 per cent earthquakes in peninsular India. The experts are yet to conclude whether the tremors are foreshocks of a larger disaster or a phenomenon that will eventually subside.

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