Explained: In Assam earthquake, reminder of seismic hazard along HFT faultline Abhishek Saha Several houses and buildings were damaged after an earthquake of magnitude 6.4 on the Richter scale hit Assam around 8 am on Wednesday. Six aftershocks, of magnitude ranging from 3.2 to 4.7, occurred in the two-and-a-half hours following the main tremor. Senior Minister Himanta Biswa Sarma posted on Twitter that the epicentre was in Dhekiajuli town in the state's Sonitpur district. Prime Minister Narendra Modi spoke to Chief Minister Sarbananda Sonowal and assured all help from the Centre. On a fault line... The primary earthquake had its epicentre at latitude 26.690 N and longitude 92.360 E, about 80 km northeast of Guwahati, and a focal depth of 17 km, the National Centre for Seismology (NCS) said.