Study links north Karnataka tremors to hydro-seismicity

The NGRI, Hyderabad, was asked to take up field inventory and earthquake related studies in and around the affected regions in Vijayapura & Kalaburagi.
The NGRI is sending a team of scientists to north Karnataka in the next two days to study and ascertain the field conditions. (REUTERS)
The NGRI is sending a team of scientists to north Karnataka in the next two days to study and ascertain the field conditions. (REUTERS)
Published on Oct 16, 2021 12:14 AM IST
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BySharan Poovanna, Bengaluru

The Karnataka government on Friday said a recent study has shown that the tremors recorded in the northern part of the state normally occur post monsoon and are related to a phenomenon called hydro-seismicity.

The Karnataka State Disaster Management Authority (KSDMA) had commissioned the National Geophysical Research Institute (NGRI) to take up a detailed analysis of the recent recordings of earthquakes in Karnataka’s Bidar, Kalaburagi and Vijayapura districts among other places after these regions witnessed tremors that were of a magnitude as high as 4.0 on the Richter scale.

“In their preliminary observations, they have indicated that the micro tremors of this nature normally occur during the post monsoon period, after a heavy rainfall, is related to a phenomenon called hydro-seismicity,” Manoj Rajan, the commissioner of the KSDMA, said in a statement on Friday.

The findings of the study come at a time when these regions witnessed around 15 instances of earthquakes and tremors, some that were felt 50-60 km away, adding to the panic of the population in these parts of the state.

“Within crustal volumes having fracture permeability, a natural increase in hydraulic head caused by transient increases in stress due to the elevation of the water table in recharge areas of groundwater basins, can be transmitted down to depths of 10-20 km, thereby triggering micro tremors and sounds are also accompanied by some of these tremors. These are due to shallow earthquakes that generate high-frequency surface waves. This type of seismic activity is very common and nothing to worry about, since it may not cascade into a large devastating earthquake,” Rajan said.

The NGRI is sending a team of scientists to these regions in the next two days to study and ascertain the field conditions.

The NGRI, Hyderabad, was asked to take up field inventory and earthquake related studies in and around the affected regions in Vijayapura & Kalaburagi.

JL Gautam, the head of operations at National Centre for Seismology (NCS), had earlier said these were minor events and they (earthquakes and tremors felt this time) were local adjustments or intra-plate activity or activity within plates, Hindustan Times reported on October 13.

The first two tremors on October 1 and 5 were recorded near Basavakalyan in neighbouring Bidar district that borders Maharashtra.

Authorities have reached out to the mines and geology department to understand the phenomena and also raise awareness among the people who have been living in constant fear over the recent events.

Rajan said that the phenomenon related to the occurrence of micro tremors originating from shallow depths associated with subterranean sounds was experienced in the past during 2006-

2009 at Hasargundgi, Yelakapalli, Yempalli, Chimanchod of Chincholi Taluk, Kalaburgi District.

“During 2010-14, 25 micro tremors in Vijayapura of magnitude 1.2 to 3.1 have been reported by the Permanent Seismic Monitoring Stations Network established by KSNDMC along with subterranean sounds. In Kalaburgi during 2016, two micro tremors of magnitude 1.5 & 1.6 respectively has been reported and in Bidar during 2017, 3 micro tremors of magnitude 2.0 to 2.2 have been reported by the KSNDMC Network,” Rajan said on Tuesday.

People of the region had spent several nights in large open areas after a series of earthquakes and tremors in the last two months. Their fears are not unfounded as Vijayapura has recorded an earthquake with a magnitude of 6.4 in 1993 with significant damage done not just in this district but also Bidar and Kalaburagi.

“Vijayapura is situated in the geological provinces of Dharwar Craton, which is an Archaean continental fragment of the Peninsular India. As per the Seismic Zonation map of Karnataka, Vijayapura District falls in Seismic Zone II & III (Figure 1c), II being Earthquake free zone and III being Moderate Earthquake Zone, the part of area where the Survey has been carried out and reports of sound heard falls in Zone II, making the less chance of occurrence of Earthquakes. The documented very first Earthquake in Vijayapura is during 1653-1654 and the details of Epicentre along with date & time are unknown. The next known Earthquake was on 15.11.1973 with a Magnitude of 4.0, epicentred at Almel-Sindgi, Vijayapura,” according to the KSDMA.

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Wednesday, December 08, 2021