Spurt in small quakes, but Nagpur in safe zone

Nagpur: There has been a spurt in swarm activity (earthquakes with small magnitude) in the region with six quakes recorded between February and March. Two earthquakes having magnitude 2.6 were recorded near Umred on Saturday too. Interestingly, they took place without anyone feeling them, because of small magnitude, less than 3 on Richter scale.No major earthquake has hit the district in recent history, with Nagpur only feeling aftershocks or mild tremors following tragedies such as Latur or Jabalpur quakes in the 1990s.

The current quake activity follows similar spurt in swarms and larger quakes (more than magnitude 3) in Seoni, around 120km from here. The spurt in Nagpur and Seoni is believed to be taking place because of renewed activity or crustal adjustments below the earth’s surface in Central India. Officially, the Geological Survey of India is yet to establish the cause.Nagpur lies close to the Gavilgarh Shear Zone while Seoni is close to the Central Indian Shear. Having a seismically silent history, Seoni began witnessing swarm or micro earthquakes from 2020 and recorded 17 events in next 13 months. By 2023, the swarm activity started occurring in Nagpur district too, as small quakes of magnitude 2 with a depth of 5-10km were recorded. This year, Seoni too has recorded three earthquakes in March.Nagpur is not included in the list of cities for Sesmic Hazard Risk Microzonation (SHRM) by the National Institute of Disaster management (NIDM), as it falls in sesmic zone II, a relatively safe area.The spurt in swarms in Seoni led to the installation of a permanent seismic station by National Centre for Seismology (NCS) at Chhindwara in July 2021. The seismic activity is also covered by 11 seismic stations at Nagpur, Jabalpur, Bhopal, Indore, Guna, Narmadanagar, Akola, Hingoli, Raipur and Kanker, spread over around 300km area. These stations are capable of locating earthquake of magnitude 2.5 and above in Seoni region.According to a report on ‘Seismic History and Recent Earthquakes in Seoni district’ by NCS, the swarm type of activity may be attributed to local crustal adjustment. “As per tectonic map, the Seoni region overlaps with seismicity since 1987… These events were found located in vicinity of Gavilgarh Shear Zone. Earthquake in MP region was found mainly associated to various tectonics,” the report states.VNIT professor Yashwant Katpatal, who is dean (research and consultancy), said shear zones are related to one another. “Ultimately, they are somewhere attached to global tectonic system. Shear zones have a repeat or readjustment period. Depending on the type of rock, stress keeps accumulating at some spots over the years. This could be an area of 50km or more. Volume and type of rock as well as length of the fault will decide the time taken for crustal adjustment. It may take 60 years or 100 years, which could be happening now,” he said.Prof Katpatal ruled out any major risk from such crustal adjustment.
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