Reasons of Manipur earthquake

Md. Oliur Rahman

Reasons of Manipur earthquake

Md. Oliur Rahman

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Geological reasons of manipur earthquake in India occurred recently.

1 Reasons of Manipur earthquake An earthquake measuring 6.7 magnitudes has hit north-east India in 4 January 2016, near its borders with Myanmar and Bangladesh, killing at least nine people. The quake struck at 04:35 local time (23:05 GMT Sunday) about 29km (18 miles) north-west of Imphal, the capital of Manipur state, according to the US Geological Survey (USGS).Strong tremors have been felt across the region. Computer models from the U.S. Geological Survey estimated that as many as 98 million people in the region may have felt the earthquake, including some 2.1 million people who may have experienced "strong" to "very strong" earthquake. The computer models suggested the likelihood of damage and casualties, noting that buildings in the region are highly vulnerable to earthquake shaking. Six of those killed were in Manipur while Bangladesh reported three deaths. The earthquake was originally reported to have measured 6.8 magnitudes. India’s said it struck at a depth of 17km (about 10 miles).The tremor cracked walls and a newly-built six-storey building in Imphal collapsed. Other buildings were also reported to have been damaged. As well as six people killed, more than were 30 injured in Manipur. In the neighbouring Bangladesh, three people were reported dead while dozens were being treated in hospital for injuries sustained during the quake. Active area The North-east is located in Zone V – “very severe intensity zone” – and covers about 12 per cent of the country’s total geographical area and about 11 per cent of the population. With the adjoining countries of Nepal, Bangladesh, Bhutan, China and Bangladesh sharing space in Zone V, what the North-east requires is a very well-drawn up disaster preparedness plan, apart from a detailed disaster mitigation policy comprising very strict construction by-laws. The region has experienced at least 18 severe earthquakes measuring above 7 on the Richter scale in the last 100 years. These include the ones that struck Shillong (1897) and AssamArunachal-Tibet (1950), with the latter changing the course of many rivers including the Brahmaputra. 2 The towering peaks of the Himalayas and the Hindu Kush, among other mountains, testify to the tectonic forces underlying the meeting point of the India and Eurasian plates. This is the 20th quake of magnitude-6 or greater to hit within 155 miles (250 kilometres) of the epicentre of Sunday's Manipur quake in the past century, according to the USGS. According to the agency, the Manipur quake originated on a strike-slip fault. These are faults that run vertically, with the blocks of crust on either side moving horizontally in relation to one another. (You can see an animation of a strike-slip fault on the USGS website.) The region where the quake struck is in a transitional zone. To the south, near Sumatra and the Andaman Islands, the India plate is slipping under the Eurasian plate in a straightforward example of seduction. This results in some strike-slip quakes, but more thrust-fault temblors, which push old rock layers over new ones at a low angle. North of the Manipur region, along the Himalayan front, the majority of earthquakes are likewise along shallow thrust faults. One example is the magnitude-7.8 quake that hit Nepal in April 2015. That quake killed more than 9,000 people, destroyed historic buildings and moved Mount Everest an inch. In between those two regions sits the transitional zone where the latest quake hit and where the geology is quite complicated. Depth and damage Deeper quakes like the Manipur temblor, which had a depth of about 34 miles (55 km), tend to cause less surface damage than those that originate higher up, in the crust. 3 Had it been a shallow earthquake, as close as it was to the town, it could have caused a lot more damage. Imphal sits in a basin, however, which could have locally amplified the quake's waves, explaining some of the damage. Local officials told news agencies today that the quake had killed at least 10 people and injured more than 100. Reports on the USGS website indicate that the Manipur quake was felt as far away as Kathmandu, which was affected by the much larger magnitude-7.8 quake last April. The USGS has not detected any significant aftershocks from the Manipur quake — a fact that could be attributed to the quake's depth. Main reason Manipur earthquake occurred in an area where the India and Eurasia tectonic plates — the slabs of planet that created the highest mountains in the world — collide. The earthquake occurred in a region where the Indian plate was moving in a north-northeast direction vis-à-vis the Sunda plate at a velocity of approximately 40 millimetres to 50 millimetres a year, producing large numbers of earthquakes that make the region one of the most seismically volatile on Earth, according to the U.S. Geological Survey. On the surface, the boundary between the plates is marked by the foothills of the Suleiman Range in the west, and the Indo-Burmese Arc in the east and the part of the Himalaya Front in the north of India. The earthquake was generated by what is known as a strike-slip fault, where sections of the Earth move like two blocks rubbing alongside each other at vertical, or nearly vertical, fracture points. The exact direction of the movement that produced the 6.7-magnitude quake isn’t so far known, but initial analysis of the seismic waveforms by the U.S.G.S suggests it was either the 4 result of a right block–known as the right-lateral fault plane–dipping slightly to the eastnortheast, or a left block dipping steeply to the south-southeast. The precise location of the fault where movement triggered the quake isn’t known, the U.S.G.S. said, but is broadly related to this plate boundary deformation at a depth of close to 31 miles, within the lithosphere, or Earth’s crust and upper mantle, of the India plate. Moderate to large earthquakes around the northeast of India are fairly common, the U.S.G.S. said. Some 19 other quakes greater than magnitude 6 have occurred within 156 miles of Monday’s temblor in the past 100 years, it said. Warning by the scientist’s The disaster management experts have warned of a bigger catastrophe, earthquakes with a magnitude of 8.2 or greater on the Richter scale which may hit the already ruptured Himalayan region. They say quakes with higher intensity than the one that struck Manipur on Monday are likely to rock the region in future. The tectonic shift a series of these recent earthquakes have caused in the region -- Manipur 6.7 (Jan 2016), Nepal 7.3 (May 2015) and Sikkim 6.9 (2011) -- have re-ruptured the plates that had already developed cracks during previous temblors. This has led to conditions which might trigger multiple earthquakes which may go up to 8.0 in magnitude. Stress has increased in the mountains of north-east since the Nepal earthquake. Monday's 6.7 magnitude earthquake in Manipur shows the stress has not been fully released, it has only become worse. "The collision between the Himalayan plate in the north and the Indo-Burmese plate in the east and the risk created as a result is the highest at this moment," according to NIDM experts. India is divided into four seismic zones. The most active Zone V comprises of the whole of north-east, parts of north Bihar, Uttarakhand, Himachal Pradesh, J&K, Gujarat and Andaman & Nicobar Islands. Delhi comes under Zone IV and is considered as one of the high-risk areas. According to MHA's own assessment, the regulatory mechanism in Indian cities that prominently figure on the disaster map are weak and any disaster striking in any one of these populous cities would cause huge casualties. Compiled by: Md. Oliur Rahman, Dept. of Civil Engineering, Leading University, Sylhet, Bangladesh. e-mail: [email protected] Sources: www.vectorews.com, www.livescience.com, www.bnonews.com, The Times of India, BBC news, www.Nelive.com

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