“The historical and instrumentally recorded earthquake data reveals that the region is affected by moderate to large earthquakes and the most prominent events among those are the 29th July, 1960 Assam earthquake of M 6.0,” said the NCS in its report to the ministry of earth sciences (MoES).
The nearby region, beyond Assam, had, however, felt two more high intensity earthquakes in the recent past with one (M 7.1) being recorded in Manipur on January 3, 2016 and another (M 6.4) in Bhutan in September, 2009.
The epicentre of the earthquake on Wednesday was located at about 80 km north-east of Guwahati; 132 km north of Shillong and 180 km west of Jorhat. It struck Assam at 7.51 am at a depth of 17 km from the surface.
Sharing its findings with the ministry of earth sciences (MoES), the NCS said damages to buildings were reported within 100 km from epicentre in the areas of Sonitpur, Nagaon and Guwahati.
“Six aftershocks of magnitude range of 3.2 to 4.7 were reported within 2.30 hours from the time of occurrence of main shock of 6.4, signifying the release of stress in the vicinity of the source zone in and around Sonitpur, Assam,” it said in its report.
The NCS said, “The preliminary analysis shows that the events are located near to Kopili Fault closer to Himalayan Frontal Thrust (HFT). The area is seismically very active falling in the highest Seismic Hazard Zone-V associated with collisional tectonics where Indian plate subducts beneath the Eurasian Plate”.
The earthquake was felt in the entire north-east region of India and some parts of Bihar, West Bengal and Bangladesh. “More than 70 felt reports due to this earthquake, have been received from Assam, Bihar, West Bengal and Bangladesh through NCS website and Mobile App having intensity ranging from I to V on Modified Mercalli Intensity (MMI) Scale,” said the report.