SEISMIC ACTIVITY IN INDIA
According to Indian Bureau of standard (BIS Code, 1983), Indian region has been divded into four seismic zones. On the basis of magnitude of damage risk India is divided into FOUR damage risk zone
| ZONE II OF LOW DAMAGE RISK: Parts of Punjab and Harayana, Parts of U.P, eastern Rajasthan, Tamilnadu, Parts of W. Bengal, Kerala.
ZONE III OF MODERATE DAMAGE RISK: Southern and south eastern Rajasthan, most of Madhya Pradesh, Maharashtra, Karnataka and South of Bihar. ZONE IV OF HIGH DAMAGE RISK: Himachal Pradesh, Jammu and Kashmir, Dehra Dun, Roorkee, Nainital, Punjab, Harayana, Bihar, Sikkim. ZONE V OF VERY HIGH DAMAGE RISK: Jammu and Kashmir, some parts of Himachal Pradesh, Uttrakhand, Kutch area of Gujarat. |
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Earthquake in India commonly occurs in narrow belts. However, 50 to 60% of the landmass of the Indian subcontinent is vulnerable to the hazards of earthquakes. However, the Himalayan arc is repeatedly shaken by moderate to Great earthquake during last one century.
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| The distribution of epicenters in the Indian subcontinent |
The northeastern region is particularly prone to high seismicity. The Kachchh-Saurashtra-Konkan belt along the West Coast is the second high-seismicity belt. There are large areas of moderate and small earthquakes in the Central Sahyadri (western Karnataka), Southern Sahyadri (central Kerala), Biligirirangan-Mahadeswaramali Ranges (southeastern Karnataka) and the Godavari basin (Andhra Pradesh). Yet another long belt of frequent earthquakes embrace the entire Narmada-Tapi valleys in Madhya Pradesh and adjoining Maharashtra. The occurrence of earthquakes implies that these are the zones where the strain generated in the Indian crustal plate is being periodically relaxed through movements on active faults. The question is: why at all do these zones have accumulated strain that is being relaxed off and on.
| Earthquake Region | Number of earthquakes of Magnitude M | Average Period of Recurrence of | |||
| 5.0-5.9 | 6.0-6.9 | 7.0-7.9 | 8.0+ | M 5.0 | |
| Northwestern and Western Himalaya | 25 | 7 | 2 | 1 | 2½ to 3 year |
| Central Himalaya | 68 | 28 | 4 | 1 | 1 year |
| Eastern Himalaya and Northeastern India | 200 | 128 | 15 | 4 | Less than Year |
| Indo Gangetic Plains and Rajasthan | 14 | 6 | 0 | 0 | 5 years |
| Khambhat-Rann of Kachchh in Gujarat | 4 | 4 | 1 | 1 | 2 years |
| Peninsular (Southern) India | 31 | 10 | 0 | 0 | 2 ½ to 3 years |
| Andaman-Nicobar Islands | 80 | 68 | 1 | 1 | Less than ¾ year |
| Region-wise occurrence of earthquakes of magnitude M 5 or above in the period 1897-1993. | |||||
The Himalaya is spread about 2500km from Kashmir (36° N, 72° E) to Arunachal Pradesh (30° N, 72°s E), which constitute the central part of the Alpine belt, is seismically one of the most active intercontinental regions of the world. The peak of Nanga Parbat (8, 125m) in the west, the peak of Namcha Parwar (7,755m) in the east and Mount Everest (8,488m) in the north comprise some of the world’s highest mountain ranges. The western Himalayan chain is divided longitudinally by principal thrusts into five tectonic zones, called the Sub-Himalaya (SH), the Lesser Himalaya (LH), the Higher Himalaya (HH), the Tethys Himalaya (TH), and the Indus Suture (IS). The principal thrusts are Himalayan Frontal Fault (HFF), Main Boundary Thrust (MBT), Main Central Thrust (MCT) and Indus Suture Thrust (IST). The Himalaya is the Eurasian and Indian plates at rates varying from 44 to 55 mm per annum. The Indian-Eurasian collision occurred in early tertiary time on the Indus suture zone. Subsequently, the thrusting shifted south, driving the northern edge of the Indian continental plate back onto itself along the Main Central Thrust (MCT) and the Main Boundary Thrust (MBT), and uplifting the Himalaya. The convergence between India and Eurasian is taken up not only by thrusting at the front of the Himalaya, but also to the north, where China and Southern Siberia. Only about 9-14 mm a-1 convergence is taken up at the Himalayan frontal zone; the rest is taken up farther north.
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Himalayan seismic map |