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April 18, 2017

Mild tremor felt in parts of Bengaluru, did quarrying activity cause it?


None of the observatories recorded the tremor

Tuesday, April 18, 2017

 Mild tremors that lasted a few seconds were felt by people living in Rajarajeshwari nagar, Jayanagar, Banshankari and Basaveshwaranagar in Bengaluru at about 8 am on Tuesday.  Residents of the area took to social media stating that they experienced tremors in the morning.

However, officials at Karnataka State Natural Disaster Monitoring Centre (KSNDMC) told TNM that none of the observatories recorded the tremor, possibly because it was less than one Richter scale.

The tremor was suspected to have been caused by some local quarry blasts as it was too local and the observatories could not record it.

Jagdish, a scientist at the KSNDMC said that quarrying in Ramanagara might have caused the tremor and that it was highly unlikely that the effect would be felt across Bengaluru.

“The nearest station is in Magadi Road, but it did not record any tremors possibly because the energy of the quarry blast was felt only in a very short distance.  Another possibility is local crustal re-adjustments, and in such cases, the signal is bound to decay within short distance before they reach the observatories. Only if they travel to larger distances can we calculate the epicentre," Jagdish said.

Speaking to Deccan Herald, Srinivas Reddy of the Disaster Management Centre said, “Our centres did not showing any such tremor. It happens when the magnitude of earthquake is less than one in Richter scale."

"My aunt saw the fridge door move and the wardrobe door close. So they ran out, they also saw some other neighbours also out of the house," Shifa Kouser, a resident of RT Nagar, told The News Minute.

Mild tremors felt in parts of Mandya and Ramanagaram

Several villages in Mandya and Ramanagaram districts experienced mild tremors lasting a few seconds on Tuesday morning. No causality or damage to property was reported from any part of the districts, senior police and revenue officials told The Hindu.

Many people residing in Vivekananda Nagar, Pete Beedhi in Channapatna, Kanakapura, Yalachi Palya, Doddagangavadi and some other areas of Ramanagaram district said they experienced tremors at 7.40 a.m.

According to reports, mild tremors were also experienced between 7.40 a.m. and 7.45 a.m. in Besagarahalli, Valagerahalli and Koppa near Maddur, JPM Layout near Halagur in Malavalli, Alakere near Mandya and some areas near Halagur and Kala Muddana Doddi.

In panic, residents of these areas came out of their houses to the streets, grounds and open spaces for safety.

The tremors and the relatively-widespread area of impact have left the Karnataka State Natural Disaster Monitoring Centre (KSNDMC) flummoxed as Mandya and the outskirts of Bengaluru are not known to have an active shear or fault line.

“We have five earthquake monitoring stations in the area, the nearest being at T.G. Halli and KRS Dam. These instruments have not recorded any activity. We even cross-checked our instruments [which have in the past measured tremor intensities of as low as 1.6 on the Richter Scale] and they are working fine,” said S. Jagadish, scientist, KSNDMC.

He said either a quarry blast or reactivating of dormant faultlines could be the reason for the tremor. “This needs deeper study and we can only speculate now. There is a fault line along Arkavathy and Vrishabhavathy rivers, and these could be re-activated slightly,” he said.

At the start of the month, the movement of a lineament (a small fault in the geological landscape) at Chitradurga-Tumakuru district border had caused a minor earthquake measuring 2 on the Richter Scale.


Two agencies, one state-run, and the other Central, vastly differ on yesterday’s earthquake intensity, casting doubts over their readings’ accuracy

Tuesday’s early morning 3-second tremor, felt in Southern Karnataka districts, has turned into a bone of contention between state-run Karnataka State Natural Disaster Monitoring Centre (KSNDMC) and Centre’s Indian Meteorological Department (IMD).

While KSNDMC said the tremor was ‘so mild’ that even their advanced equipment could not record it, the IMD recorded an earthquake of 3.4 magnitude on the Richter scale its epicentre at 30 Km depth below Ramanagara, just 50 Km southwest of Bengaluru.

The separate seismic measurements by both have raised doubts over their accuracy.

At around 7.35 am on Tuesday residents of Rajarajeshwarinagar, Kengeri, Bengaluru South and East felt the tremor, and some even ran out of their houses in panic.

As panic spread thanks to social media, KSNDMC felt there was no reason to fear, reporting it as only a ‘micro tremor’ that went unnoticed on the Richter scale.

But the IMD recorded an earthquake of 3.4 magnitude with its epicentre at Ramanagara (12.6N, 77.4E), at a depth of 33 km.

Rajarajeshwarinagar resident Joseph Hoover, said, “I felt the tremor when the window glasses began to rattle. I had experienced it in the past and knew it was a quake.

My wife thought it was due to a heavy truck passing by. When I posted the experience on social media, many others joined in with their experiences.” When people
called KSNDMC control room for more information, the centre issued an advisory note, saying, “A micro tremor has been felt in the areas of Channapattana,
Ramanagara, Kanakapura. The strength of the micro tremor as reported may be of a very low magnitude (less than 1.0) due to which the tremor was not recorded by our network.”

But KSNDMC was shocked when IMD website said an earthquake of 3.4 magnitude with epicentre at Ramanagara was recorded.

“I don’t understand how they could arrive at such a huge magnitude when nothing was recorded on our instruments. Our seismic measurement instrument network are installed at 12 locations and five places in Southern Karnataka—TG Halli, KRS, Hemavathi Dam, Harangi Dam and Gundal Dam – are so advanced that none of them have recorded any such tremors,” Dr GS Srinivasa Reddy, director, KSNDMC, told Bangalore Mirror.

A duty officer at IMD observatory on Palace Road in Bengaluru, confirmed recording an earthquake of magnitude of 3.4 at Channapattana in Ramangara district near to Bengaluru.

KSNDMC director Reddy said, “The USA-based United States Geological Survey (USGS) is the pioneer in the world to record tremors of any level and they update such events on every second basis. The Hyderabad-based Indian National Centre for Ocean Information Services (INCOIS) is the second most scientific body and known for its forecast in entire Asia. Neither recorded any tremors; nor did our system. I wonder how IMD could record such a huge magnitude when none of us recorded anything at the same time.”

The KSNDMC uses VSAT-enabled permanent seismic monitoring stations network along with broadband seismic stations—supposedly the advanced instruments to record seismic activities currently. Yet, the panels did not record any tremor.

KSNDMC in its advisory to the government said: “These low magnitude micro tremors, which are less than 1.0, do not cause any damage to life or property although there may be light shaking and cracks formed depending on the mode of local construction and the perception of the local community. As the micro tremors are of low magnitude, there is no need to panic.”

Jagadeesh, scientist with KSNDMC, explained that Karnataka lies between seismic zones 2 and 3 – the safest in seismic safety. “There is no immediate danger or threat following the earthquake because of the seismic zones that the state comes under.”

Updated: Apr 19, 2017, 12.53 AM IST