Representative image of a limestone mine.
Credit: PTI Photo
Kalaburagi: Frequent moderate tremors have created panic among people of districts in Kalyana Karnataka.
Scientists have attributed this to heavy rainfall in limestone areas as one of the main reasons, increasing the pore fluid pressure in underground fissures and fault lines.
This pressure acts like a hydraulic jack, pushing rocks apart and allowing critically stressed faults to slip, causing moderate magnitude earthquakes.
Kalaburagi and Bidar districts have witnessed four moderate tremors in the last two weeks.
The region is known for its hot and arid conditions due to extensive limestone deposits. Districts like Kalaburagi, Bidar and Yadgir have major repositories of high-grade limestone.
Scientists at the Karnataka State Natural Disaster Monitoring Centre (KSNDMC) said these districts witnessed heavy rainfall and floods this year leading, to large and rapid increase in the amount of water stored underground, significantly raising the water table and hydraulic head within rocks.
The pressure provides the push to trigger a rupture and earthquake, they said.
Increase of water storage in major reservoirs like Almatti, Narayanapura across Krishna river and several barrages across Bhima river, due to excess rainfall, resulted in groundwater recharge.
So, the water pressure beneath the earth causes mild earthquakes up to a magnitude of 3 on Richter scale. The tremors are accompanied by a loud, rumbling sound.
Stone quarrying activities in Sindagi and other parts of the region are another reason, scientists said. They said several districts of Kalyana Karnataka had witnessed similar tremors in 2016, when heavy rainfall devastated the region.
KSNDMC director M S Diwakar said the exact reason for the tremors cannot be correlated with any factors at this juncture and directions will be given to scientists of the centre to conduct thorough study.
“I will get a report from scientists after the study,” he said.
Seismic zone II
Two mild earthquakes, epicentered 4.5 km west of Mudnal village in Humnabad taluk of Bidar district and 2.5 km north-west of Hallikhed (K) in Humnabad taluk, were reported in the morning hours of October 30 and 31.
KSNDMC scientists said people need not panic as the region falls under seismic zone II, wherein the possibility of damage due to earthquake is very less. Also, the epicenter is void of structural discontinuities as per tectonic map. There is the highest risk of earthquake and destruction only in seismic zone-5 areas, they said.
Mines and deology department deputy director Somashekhar M said he had written to the district administration to form an expert team to conduct a study.
‘No need to panic’
“Limestone is primarily composed of calcium carbonate and there will be a reaction if these deposits encounter with water, resulting in heavy sound due to tremors. People need not panic as intensity is low and not destructive. However, people should avoid living in old and dilapidated homes, schools as there are chances of building collapse,” he said.