Earthquake

Earthquake is amongst the most terrifying of all natural phenomenons. Striking without warning, and seemingly coming out of nowhere, these challenge our inherent assumptions about the stability of the very planet we live upon. Any shaking of the earth, whether lasting for minutes or only for seconds, seems eternal to those who experience it. Amild quake may inspire no more than passing interest, but a powerful one can wreck awesome devastation.

The Earthquake Risk in India

India's increasing population and extensive unscientific constructions mushrooming all over, including multistoried luxury apartments, huge factory buildings, gigantic malls, supermarkets as well as warehouses and masonry buildings keep - India at high risk. During the last 15 years, the country has experienced 10 major earthquakes that have resulted in over 20,000 deaths. As per the current seismic zone map of the country (IS 1893: 2002), over 59 per cent of India’s land area is under threat of moderate to severe seismic hazard-; that means it is prone to shaking of MSK Intensity VII and above (BMTPC, 2006). In fact, the entire Himalayan belt is considered prone to great earthquakes of magnitude exceeding 8.0-; and in a relatively short span of about 50 years, four such earthquakes have occurred: 1897 Shillong (M8.7); 1905 Kangra (M8.0); 1934 Bihar-Nepal (M8.3); and 1950 Assam-Tibet (M8.6). Scientific publications have warned of the likelihood of the occurrence of very severe earthquakes in the Himalayan region, which could adversely affect the lives of several million people in India.

Earthquake threat in the Himalayas and Uttarakhand

Earthquake hazard potential is assessed to be particularly high in the entire Himalayan terrain and in the past the region has been jolted by four great earthquakes, apart from Kumaun Earthquake of 1720 and Garhwal Earthquake of 1803. The peak ground acceleration ( PGA ) in Shillong Earthquake of 1897 is estimated to have exceeded 1g (Oldham, 1899), while around 18,000 persons were reportedly killed in 1905 Kangara Earthquake (Middlemiss, 1910). Entire Himalayan terrain falls in Zone V and Zone IV of Earthquake Zoning Map of India (IS 1893 (Part 1), 2002) that divides the Indian landmass into four distinct risk zones; Zone II to Zone V. Earthquake intensity can reach VIII on MSK Scale in Zone IV, while in Zone V it can reach IX or even more. In the recent past (1991 and 1 9 9 9 ) the State of Uttarakhand has witnessed the devastation caused by two earthquakes (Uttarkashi and Chamoli) and being traversed by major Himalayan tectonic discontinuities (Himalayan Frontal Fault; HFF, Main Boundary Thrust; MBT and Main Central Thrust; MCT) the State is often shaken by earthquakes of lesser magnitude. The State of Uttarakhand has however not experienced a great earthquake (Mw ≥ 8.0) for more than previous 200 years and constantly accumulating strain thus remains due for release in this sector. The region is thus shown as falling in the seismic gap of 1934 and 1905 great earthquakes (Yeats and Thakur, 1998). Since smaller earthquakes do not occur sufficiently frequently to accommodate the observed convergence of Indian and Eurasian plates, there is progressive strain built up in what are recognized as seismic gaps (Bilham et al., 1998). Falling in seismic gap entire State of Uttarakhand is interpreted to have accumulated potential slip for generating future great earthquakes (Khattri, 1987). Having been identified as a potential region for a future catastrophic earthquake is a cause of concern for one and all, particularly those living in this region.


Cached at 21/10/2018 03:35:01