On 28th April 2021, a moderately severe earthquake hit Assam and parts of north-east India. The 6.4 magnitude Earthquake had epicentre at Dhekiajuli in Sonitpur district of Assam, and the focal point was 17 metres below ground level. The epicentre is located just 80 km northeast of Guwahati, the largest city in north-east India. The area falls under Seismic hazard zone V, which most prone to massive Earthquakes.
The Himalayan Frontal Thrust, or the Main Frontal Thrust, is a major geological fault along the Indian and Eurasian tectonic plate boundaries. Many parts of Assam, including Sonitpur, falls near the area of Himalayan Frontal Thrust and is thus prone to significant Earthquakes. The 8.6 magnitude Assam earthquake of 1950 severely damaged the whole state and the neighbouring states of Arunachal Pradesh, Nagaland, Manipur, Mizoram and Meghalaya. This time, as the earthquake’s magnitude was not that severe, many areas, including Guwahati, felt tremors but were not severely damaged.
The earthquake occurred specifically at Kopili fault, a 300 km long part of Himalayan Frontal Thrust stretching from Bhutan to Mayanmar following the foothills of the Himalayas. The Kopili fault is one of the most seismically unstable faults that have produced earthquakes since prehistoric times. The Kopili fault has been quiet for some time, some time and the earthquake released much of the stress building up in the crust. That is the reason for the severity of the quake. The last major earthquake in the region was of 6.0 magnitude on 29th July 1960.
According to the latest reports, two died of shock and at least 10 others sustained injuries in the earthquake. Several buildings and roads in the western part of Assam are damaged. The nearby Arunachal Pradesh districts also felt the tremors where two people are injured after their house collapsed. There was also a report of a minor landslide in West Kameng district induced by the quake, that blocked a vital road in the area.
The earthquake’s timing and duration were the primary cause that it averted any significant damage. The earthquake occurred early in the morning and for a short duration of fewer than 30 seconds. Had the tremor occurred midday, there might have been damages to workers working in high rise buildings and offices. Also, an earthquake persisting for more than 30 seconds will bring more damage to the facilities. However, there were six aftershocks ranging between 3.2 to 4.7 magnitude, which has not caused any significant destruction. Let us hope that no more damaging aftershocks occur amid the pandemic situation in India.
Written by – Himadri Paul