Earthquake Vulnerability of India
India has a very high frequency of great earthquakes. The reasons of high magnitude earthquakes in India are hidden in the tectonic setting of India. India is currently penetrating into Asia at a rate of approximately 45 mm/year and rotating slowly anticlockwise. This rotation and translation results in left-lateral transform slip in Baluchistan at approximately 42 mm/year and right-lateral slip relative to Asia in the Indo-Burma ranges at 55 mm/year. At the same time, deformation within Asia reduces India’s convergence with Tibet to approximately 18 mm/year. Since Tibet is extending east-west, there is a convergence across the Himalaya that results in the development of potential slip available to drive large thrust earthquakes beneath the Himalaya at roughly 1.8 m/century.
Seismic Zoning of India
Indian subcontinent has a long history of devastating earthquakes, partially due to the fact that India is driving into Asia. More than 50% area of Indian Subcontinent is vulnerable to earthquakes. According to the IS 1893:2002 (It is the latest code of Bureau of Indian Standards (BIS) which lays down the criteria of for earthquake resistant design of structures), India has been divided into four seismic zones viz. Zone-II, -III, -IV and -V unlike its previous version which consisted of five zones for the country. After some revisions in the previous zoning, Zone I was altogether removed.
This zoning has been done on the basis of MSK-64 scale and a IS code Zone factor has been assigned by the BIS to each of them. The zone factor of 0.36 is indicative of effective (zero period) peak horizontal ground acceleration of 0.36 g (36% of gravity) that may be generated during MCE level earthquake in this zone. They are presented in the following table with IS code.
|MSK-64||Seismic Zone||Zone Factor|
|VI. Strong||Zone II|
This region is liable to MSK VI or less and is classified as the Low Damage Risk Zone
|VII. Very Strong||Zone III|
The Andaman and Nicobar Islands, parts of Kashmir, Western Himalayas fall under this lone.
This zone is classified as Moderate Damage Risk Zone which is liable to MSK VII.
|VIII. Damaging||Zone IV|
This zone is called High Damage Risk Zone and covers Indogangetic Basin, Delhi, Jammu and Bihar
|IX. Destructive||Zone V|
Zone 5 covers areas with the highest risk zone that suffers earthquakes with intensity of IX and greater. It includes Kashmir, Punjab, Western and central Himalayas, North East India and Rann of Katch
Earthquake Vulnerability of India
As per the latest seismic zone map, around 59 per cent of India’s land area is vulnerable to moderate or severe seismic hazard, implying that it is prone to shaking of MSK intensity VII and above. In the recent past, most Indian cities have witnessed the phenomenal growth of multi-storied buildings, super malls, luxury apartments and social infrastructure as a part of the process of development. The rapid expansion of the built environment in moderate or high-risk cities makes it imperative to incorporate seismic risk reduction strategies in various aspects of urban planning and construction of new structures.
Vulnerability of Himalayan Zone
The entire Himalayan Region is considered to be vulnerable to high intensity earthquakes of a magnitude exceeding 8.0 on the Richter Scale, and in a relatively short span of about 50 years, four such earthquakes have occurred viz. Shillong, 1897 (M 8.7); Kangra, 1905 (M.8.0); Bihar–Nepal, 1934 (M 8.3); and Assam–Tibet, 1950 (M 8.6). Scientific publications have warned that very severe earthquakes are likely to occur anytime in the Himalayan Region, which could adversely affect the lives of several million people in India.
Earthquake Vulnerability and Traditional Housing Construction in Rural Areas
There are several indigenous earthquake-resistant house constructing processes in India, for example:
- bhongas in the Kutch Region of Gujarat
- dhajji diwari buildings in Jammu & Kashmir
- brick-nogged wood frame constructions in Himachal Pradesh
- ekra constructions made of bamboo in Assam.
These traditional methods are increasingly being replaced with modern Reinforced Cement Concrete (RCC) buildings, often without incorporating earthquake resistant features and without compliance to building codes and bye-laws.
It is thus necessary to empower communities to ensure the seismic safety of the built environment by encouraging the use of simple, easy and affordable technical solutions and institutional arrangements. These make use of indigenous technical knowledge and locally available materials in the construction of earthquake-resistant buildings in suburban and rural areas.
Critical Areas of Concern for The Management Of Earthquakes In India
Today, majority of the buildings constructed in India, especially in suburban and rural areas, are non-engineered and built without adhering to earthquake-resistant construction principles. Most contractors and masons engaged in the construction of these buildings are also not familiar with the earthquake-resistant features specified in the building codes. The critical areas of concern for the management of earthquakes in India include the:
- Lack of awareness among various stakeholders about the seismic risk;
- Inadequate attention to structural mitigation measures in the engineering education syllabus;
- Inadequate monitoring and enforcement of earthquake-resistant building codes and town planning, bye-laws;
- Absence of systems of licensing of engineers and masons;
- Absence of earthquake-resistant features in non-engineered construction in suburban and rural areas;
- Lack of formal training among professionals in earthquake-resistant construction practices; and
- Lack of adequate preparedness and response capacity among various stakeholder groups