This quake went a lot deeper within

The low-magnitude earthquake that shook parts of Hyderabad last week was the deepest to have occurred in the city in the last 30 years, seismic experts have learnt.

To understand why the recent earthquake, measuring only 1.8 on Richter scale, was felt 26 kilometres away from the epicentre area when earthquakes of larger magnitude in the past were largely felt locally, scientists at the city-based National Geophysical Research Institute (NGRI) precisely located the earthquake’s epicentre.

However, as there were no stations in the north-western parts of the city, triangulating the location was not easy. Help came from the International Institute of Information Technology (IIIT), located at Gachibowli, where structural engineers studying buildings had equipped a building with seismic sensors. These sensors had incidentally picked up the earthquake.

With enough information available, researchers learnt that the earthquake had its epicentre in the vicinity of Umda Sagar Lake, close to Pahadishareef. The location of the quake was pinpointed on the intersection of two small but seismically-active fault lines.

They also worked out that the earthquake had occurred at a depth of seven to nine kilometres.

Earthquakes in the past, including those having their epicentres at Vanasthalipuram (2010) and Jubilee Hills (1998) were relatively shallow.

“Earthquakes in the recent past occurred within two km below surface. As the recent earthquake was relatively deep, its effect had a greater spread.

Also, the granite in the crust underneath the city facilitated energy dispersion from the epicentre,” said D. Srinagesh, chief of the seismic observatory at NGRI.

Given the earthquake’s small magnitude, no damage was reported.

Though considered safe in seismic terms, experts do not rule out a moderate magnitude earthquake, measuring up to 5, like the Medchal earthquake of 1983, in the city.

Head of the Earthquake Engineer Research Center at IIIT-H, Pradeep Kumar Ramancharla, who assisted the NGRI by providing information about the recent earthquake, expressed concern over medium-sized buildings in the city.

“Medium-sized buildings with up to six floors are a concern as these are constructed without skilled assistance and often, in violation of earthquake norms,” he said.

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Printable version | Oct 27, 2021 7:59:31 PM | https://www.thehindu.com/news/cities/Hyderabad/this-quake-went-a-lot-deeper-within/article6846977.ece

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