Sikkim Earthquake of 2011

November 30, 2011

The September 18, 2011 India-Nepal border region earthquake of magnitude 6.9 occurred near the boundary between the India and Eurasia plates, in the mountainous region of northeast India near the Nepalese boarder.

Initial analyses suggest the earthquake was complex, likely a result of two events occurring close together in time at depths of approximately 20 km beneath the Earth’s surface.

At the latitude of the September 18 earthquake, the India plate converges with Eurasia at a rate of approximately 46 mm/yr towards the north-northeast. The broad convergence between these two plates has resulted in the uplift of the Himalayas. The preliminary focal mechanism of the earthquake suggests strike slip faulting, and thus an intraplate source within the upper Eurasian plate or the underlying India plate, rather than occurring on the thrust interface plate boundary between the two.

Background:

This region has experienced relatively moderate Seismicity in the past, with 18 earthquakes of M5 or greater over the past 35 years within 100 km of the epicenter of the September 18 event. The largest of these was a M 6.1 earthquake in November of 1980, 75 km to the southeast.

Facts & Notes:

Magnitude : 6.9
Epicenter: Kanchenjunga Conservation Area
Hypocenter: 19.6 Kms below earth’s surface
The earthquake was felt across northeastern India, Nepal, Bhutan, Bangladesh and southern Tibet. 111 people were confirmed killed by the effects of the earthquake, and hundreds of others sustained injuries. As the earthquake occurred in the monsoon season, heavy rain and landslides rendered rescue work more difficult.
Recent Himalayan earthquake is an urgent wake-up call for all concerned – the government, policymakers and law enforcers.
The scale of devastation in its trail has raised critical concerns about India’s preparedness to deal with quakes of much greater intensity. The Japan experienced earthquakes this year measuring 8.9 on the Richter scale – releasing energy a thousand times greater than the current Himalayan quake – should serve as a sober reminder.
Given that over 58.6% of land in India is vulnerable to tremors, the National Disaster Management Authority (NDMA) has identified quakes as a major issue of concern. As many as 38 of India’s cities, including Delhi, Kolkata, Mumbai, Chennai, Pune and Ahmedabad, fall within moderate-to-high risk seismic zones.
An earthquake on the scale that Japan experienced would lay waste whole cities in India.
Quakes do not kill people, buildings do, so safety essentially lies in ensuring quake-resistant construction of buildings.
The NDMA has mandated all new constructions to be earthquake-resistant, especially in seismic zone cities. Earthquake engineering codes and quake-safe construction guidelines have been laid down by government bodies. But the real worry is about their enforcement.