Lucknow less prone to quakes due to Ganga

Lucknow is less prone to earthquake damages as it lies in the Ganga Plain that act as a shock absorber to reduce the impact of tremors.

However, experts said, the activeness of Himalayan Frontal Fault, which separates Himalayas from the Ganga Plain, has become more active in the past three decades, resulting in the increase of the frequency of earthquakes in this region.

Dhruvsen Singh, a professor of Geology in Lucknow University, who has done extensive research on this subject, explained that as the Indian sub-continent plate is moving towards Eurasian plate in the north direction, this at times, results in tectonic activity, which causes earthquakes in the Himalayas.

There are five major seismic or earthquake zones in India classified based on risk of damages. Each zone indicates the effects of an earthquake at a place based on the observations of the affected areas.

Zone 1 has no or the least risk, while zone 5 has the highest.

“Lucknow is at moderate risk because it is located on the Ganga plains that comes under seismic zone 3. The Ganga plain is made up of loose unconsolidated sand, silt and clay known as alluvium. The loose alluvium acts as a shock absorber that reduces the intensity of the earthquakes. The surface manifestations of all those tectonic features — ridge and fault lines which cause earthquakes — are absent in Ganga plain,” he explained.

He also said that due to the activeness of Himalayan Frontal Fault, the rate of earthquakes in Himalayan belt has increased in the past three decades.

However, most of the earthquakes have been of smaller magnitudes.

“Occurrence of smaller earthquakes is safer because they release energy generated due to movement of tectonic plates from time to time, thus preventing a major earthquake, which can cause more damage,” he added.

Hydrogeologist R.S. Sinha pointed out another area of concern.

“Our preliminary studies show that the shocks felt in Lucknow following moderate earthquakes in the past few years have been more in comparison to similar situations about 20 years ago,” he said.

“A reason behind this could be the relentless extraction of groundwater. The groundwater naturally binds the soil layers beneath the earth surface and creates high elasticity, which in turn acts as a shock absorber. This elasticity has declined significantly because about 100 metres strata below the ground in Lucknow have dried up. We found the same thing in the 2014 earthquake and informed authorities.”

Other geologists said that rapid groundwater depletion is a matter of concern and immediate preventive steps should be taken, but more studies are required to substantiate whether groundwater can check intensity of earthquake shocks.

20221110-145002

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