Assam quake tremor and vulnerability of North East India

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  Assam quake tremor and vulnerability of North East India

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• The shock: The North East was a highly fragile and earthquake-prone zone and needed to have an integrative disaster plan to tackle high-intensity earthquakes, according to scientists. But disaster mitigation policy makers in the region were yet to tap adequately into the scientific data available on earthquakes. There is a considerable knowledge and policy gap regarding earthquakes. Scientific research findings on the Kopili fault earthquake zone have hardly made it into disaster reduction policies. Bridging this gap is key to formulating any meaningful earthquake damage mitigation plans.
• Latest quake: The quake in April, measuring 6.4 on the Richter Scale, occurred near Dhekiajuli in the Sonitpur district of Assam at about 7:51 am April 28, 2021, 80 kilometres northeast of Guwahati.

1. Its epicentre was at 26.690 N and 92.360 E, according to the National Centre for Seismology (NCS). It had a depth of 17 km and lasted for nearly 30 seconds. Multiple aftershocks ranging from 4.7-3.6 on the Richter scale were also recorded within the next hour.
2. The jolts were the most severe among the ones many had witnessed in their entire lives. It kept jolting for a couple minutes and it felt like everything around me will crumble down.
3. Damages to buildings and structures have been reported within 100 km from the epicentre in the areas of Sonitpur, Nagaon, Guwahati and Udalguri, according to the Central Seismological Observatory, NCS, Shillong and Regional Meteorological Centre of the India Meteorological Department, Guwahati.

• The Kopili fault: The tremors have been attributed by the NCS to the Kopili fault zone closer to Himalayan Frontal Thrust. This is a seismically active area falling in the highest Seismic Hazard Zone V. It is associated with collisional tectonics because of the Indian Plate subducting beneath the Eurasian Plate. Subduction is a geological process in which one crustal plate is forced below the edge of another.

1. The Kopili fault zone is a 300 km long and 50 km wide lineament (linear feature) extending from the western part of Manipur up to the tri-junction of Bhutan, Arunachal Pradesh and Assam. The fault itself is a transpressional fracture that generates lower crustal dextral strike-slip earthquakes.
2. The Kopili fault is currently the most active seismic zone in North East India. Squeezed between the subduction and collision zones of the Himalayan belt and Sumatran belt, the North East is highly prone to earthquake occurrences.
3. Geodesy is an earth science of accurately measuring and understanding the Earth's geometric shape, orientation in space and gravitational field.

• More details: A tectonic depression filled up by the alluvium of the Kopilli river and its tributaries, the Kopili fault zone has witnessed many seismic activities in the past including the 1869 earthquake (7.8  magnitude) and the 1943 earthquake (7.3 magnitude). A study attributed the January 4, 2016 earthquake in the Imphal Valley to the Kopili fracture although later research contradicted this conclusion.

1. There was a gap of 74 years between the two major earthquakes of 1869 and 1943. Multiple studies predicted a major earthquake event around 2017.
2. Recent seismicity discovered along the Kopili fault led to speculations that this fault is one of the most seismically active faults of the region and a major earthquake could be expected in the future, which has somehow been validated by recent event.
3. A considerable portion of the Kopili fault zone and its neighbouring areas are characterised by alluvial soils that have a higher potential of trapping seismic waves, making the region the most earthquake prone zone in North East India.

Read more on - Polity | Economy | Schemes | S&T | Environment

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