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Unfamiliar lineament among Assam earthquake factors

A man shows the cracks on a wall at an apartment building in Guwahati on April 28, 2021, after a strong earthquake hit Assam in northeastern India, damaging buildings, but there were no immediate reports of casualties.   | Photo Credit: AFP

An unfamiliar lineament is among four factors behind frequent earthquakes in northern Assam’s Sonitpur area.

A lineament is a linear feature in a landscape dictated by an underlying geological structure such as a fault.

According to the Geological Survey of India (GSI), Sonitpur district lies within a tectonically complex triangular area bounded by the east-west trending Atherkhet Fault, the northwest-southeast trending Kopili Fault and a north-south trending lineament.

The two faults and the lineament, along with the oblique convergence of the Indian plate, have caused frequent earthquakes. The National Centre of Seismology recorded 29 earthquakes of magnitude varying from 2.6 to 4.7 in Sonitpur after the 6.4 tremblor on April 28 that damaged several buildings, bridges and a river embankment.

The last of these 29 earthquakes with Sonitpur as the epicentre was recorded early Wednesday morning. Five more of magnitudes 2.6-3.2 were also recorded in neighbouring districts during this period.

“Sonitpur was the epicentre of this huge 6.4 earthquake after 33 years because of the tectonic complexity. The Atherkhet and Kopili faults, the north-south lineament and the oblique convergence of the Indian plate is causing repetitive earthquakes,” GSI’s Deputy Director-General Sandip Kumar Som said.

“Both the Atherkhet and Kopilli are active but we do not know about the nature of the lineament involved.”

Atherkhet and Kopili are not the only faults that impact the Sonitpur region. The Siang Fracture, Yemla Fault, Namula Thrust and Canyon Thrust are spread across the northeast and are active along with Main Himalayan Thrust, Main Boundary Thrust, Main Central Thrust and several subsidiary faults.

“The northeast is demarcated as Seismic Zone V, which indicates a zone with high vulnerability. The Indian plate is moving northeast toward the Eurasian plate in the Himalayan region, their oblique collision and release of stress and strain accumulated in the local tectonic or fault environments lead to earthquakes,” Dr. Som said.

He also explained why water was oozing out of the fault in Sonitpur and adjoining affected areas after the April 28 earthquake. “This was a result of severe liquefaction [the process of making something liquid] from the unconsolidated substratum [underlying layer of soil/rock],” he said.

The GSI specialist advised people not to heed earthquake predictions.

“Unlike a landslip, a surficial process that can be constrained, an earthquake is a process deep inside the earth. But scientists worldwide are trying for a breakthrough. The work to understand the strain localisation of future earthquakes is under progress,” Dr. Som said.


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Printable version | Jun 13, 2021 10:34:59 PM | https://www.thehindu.com/news/national/other-states/unfamiliar-lineament-among-assam-earthquake-factors/article34491054.ece

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