New paper says this is because very less seismic energy has been released since the 1975 Kinnaur earthquake
If an earthquake hits the North West Himalayan region (Garhwal and Himachal Pradesh) in the future, its magnitude might be greater than 8 on the Richter scale, predict scientists.
This, they say, is because only 3-5 per cent of energy has been released since the last ‘great event’ of the 1975 Kinnaur earthquake.
“The estimated earthquake potential prevailing in the western Himalayan seismic gap lying between the epicentral zone of the 1905 Kangra earthquake and the 1975 Kinnaur earthquake reveals that the total amount of energy released since the last great event is only a fraction (3–5 per cent) of the accommodated energy,” says the research paper published in June last year in the Journal of Asian Earth Sciences by a group of scientists from different institutes.
“This suggests that if an earthquake hits this NW (North West) Himalayan segment in the future, its magnitude might be greater than or equal to 8.0,” the paper adds.
The objective of the study was to estimate the characteristics of or predict what kinds of large earthquakes could occur in the NW Himalayan (India) region in the future. The analysis was carried out using high-quality seismic data that was acquired using broadband seismometers from 2004-2013.
The paper studied the seismicity of the NW Himalayan area which was hit by four destructive moderate to great earthquakes since the beginning of the 20th century: the Kangra earthquake, 1905; the Kinnaur earthquake, 1975; the Uttarkashi earthquake, 1991; and the Chamoli earthquake, 1999.
“The Himalayan surface has been ruptured by several great earthquakes since the last century (1905 Kangra, 1934 Bihar-Nepal, 1950 Assam, 2005 Kashmir, 2015 Nepal) and a portion of the total accommodated energy has been released during these events. The various major seismic gaps in the Himalayas (western gap, central gap, and eastern gap) are still in the process of releasing the energy accumulated in the form of elastic deformation,” the paper says.
It predicts three different scenarios to calculate the earthquake magnitude potential.
In scenario one: If the 70 km wide flat part of the Main Himalayan Thrust (MHT) is participating in strain accumulation since the last event, it has approximately accommodated a seismic moment which is equivalent to moment magnitude of 7.9.
In scenario two: The ∼35 km wide mid-crustal ramp below the higher Himalayas has accommodated energy and would result in a 7.6 magnitude event.
Scenario three says that if the flat and ramp together participate in a single giant earthquake like the 1934 and 1950 earthquakes, that would result in a magnitude greater than 8 event.
“The NW Himalayas comprising the Garhwal and Himachal section is characterised by flat and ramp geometry consisting of two crustal ramps below the MHT in Higher Himalaya and the STD (South Tibetan Detachment) in the Tethys Himalaya. These fault segments can act independently or as an individual entity with a capability to trigger great earthquakes (Magnitude greater than or equal to 8.0),” the report says.
However, Sushil Kumar, scientist at the Wadia Institute of Himalayan Geology (WIHG), Dehradun, and one of the authors of the study, said that it would be wrong to say that the rest of the energy is accumulated inside the earth’s surface.
“It could have been released in the form of small earthquakes in the last few years and a separate study needs to be done to understand this better,” he said.
The research was done by scientists from WIHG, National Geophysical Research Institute, Hyderabad, National Centre for Earth Sciences Studies, Kerala, and Indian Institute of Technology, Kharagpur.
“The observed seismicity in the region signifies a higher level of tectonic activity in this region. This also gives an explanation for the reactivation of the ‘the Kauirik fault’ (which triggered the 1975 earthquake) which can lead to a considerable number of earthquakes in Himachal Pradesh,” it adds.
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