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BANGALORE: Mild tremors, measuring 0.22 g (where g refers to vertical acceleration due to gravity), from Wednesday night caused panic among residents of the Kolar Gold Fields.
Director of the National Institute of Rock Mechanics R.N. Gupta said four tremors were recorded. The first one lasting 32 seconds was reported at 11.50 p.m. It was followed by tremors at 1.45 a.m., 5.50 a.m. and 6.30 a.m. on Thursday. The impact of the tremors was felt even at far-off places such as Malur, Kolar and Bangarpet in Kolar district.
"We measure earthquakes in the area but we do not monitor the tremors that occur in the gold fields," said Mr. Gupta. The instrument at the institute measures the acceleration of the tremors. "We have no way of converting these measures into the Richter scale," he said.
Mr. Gupta noted that recently when the earthquake devastated Jammu and Kashmir and also Pakistan, there were tremors in KGF too.
The occurrence of tremors in the gold fields is not a new phenomenon. It has been happening since the mines were opened in the 1880s, according to V.S. Prakash, Director of the Karnataka State National Disaster Monitoring Cell.
He said that when the mines were very active in the 1970s and 1980s, the tremors used to be a weekly occurrence. "People working in the mines used to flee the place. They had to stop work for many days in a week because of the tremors," he said.
The only difference now, Mr. Prakash said, was that since the State-run Bharat Gold Mines Ltd. closed the fields in 2000, no one was keeping a close watch on the occurrence of these tremors. "They continue to happen in the closed mines with regularity but no one focuses on it too much these days."
Seismologists say these tremors are not related to a natural earthquake, which occurs due to movement of fault lines, but because of rock bursts in the mines. They say very often rocks get loose and fall in the shaft. The energy released from the fall causes the tremors. "These tremors are not earthquakes," said Mr. Gupta.
V.R. Gaur of the CSIR Centre for Mathematical Modelling And Computer Simulation, Bangalore, said the frequency of the tremors increases with the onset of rain. "During the rain the friction that holds together rocks diminishes and the rocks fall to the ground," he said.
The intensity of the tremors depends on the depth to which these rocks fall, say seismologists. Since the Kolar Gold Fields have very deep mines, the Champion Reef, which has been recognised as one of the deepest in the world-3.2 km below the surface, the tremors are around 02 to 04 g. "If the mines had been less deep, the tremors would have been less intensive," Mr. Gupta said.
Seismologists say that these tremors will continue.
R.N. Iyengar of the Indian Institute of Science said it was better that the gold fields get repeated small tremors than a large one. "When small rocks keep falling down, the energy they release is far smaller than all of them snowballing together," he said.
Prof. Iyengar said that there was no danger from these tremors. "I do not think that their intensity will become very big and cause a major disaster," he said.
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