Seismically very active
With the Himalayan region being one of the most seismically active places in the world, the recent earthquake, however did not come as a surprise. Most other major earthquakes above magnitude (M) 8.0 in Shillong (1987), Kangra (1905), Bihar-Nepal border (1934), Arunachal Pradesh (1950) and many others between M 6 and 7 were caused by faults formed by the under-thrusting of Indian plate below the Eurasian plate. The Sikkim region experienced relatively moderate seismicity over the past 35 years with temblors of M 5 or greater occurring within 100 km of the epicentre of the September 18 event.
Large area impact
Dr. Chadha said another interesting feature of the recent earthquake was that it was felt over a large area, including Delhi and other major cities such as Lucknow, Patna and Ranchi along the Indo-Gangetic plains. With most of the region lying in the soft sediments in the Indo-Gangetic plains and the Brahmaputra Valley, the earthquake was felt strongly as the seismic waves get amplified in soft sediments when compared to hard rock regions. As experienced earlier, such temblors would cause damage in faraway regions too due the amplification process. The amplification phenomenon again showed that major cities located in the Indo-Gangetic plains face greater earthquake hazard than other regions.