Study attributes complex tectonic linkage in Indian plate to great Assam earthquake of 1950

Researchers have traced the great Assam earthquake of 1950 (8.6 in Richter Scale) to complex tectonics of the North Eastern fringe of the Indian Plate in the Eastern Himalaya and the Indo-Burma Ranges (IBR) and the interactions between the two, which can produce deeper earthquakes in IBR and crustal ones in the Eastern Himalaya.

They have suggested that this seismic structure forms a complex tectonics which produced the great Assam earthquake and may be building up stress for a future earthquake.

The Great Assam Earthquake is the largest intra-continental earthquake ever recorded, which was located at the India-China border near the Mishmi Hills of Arunachal Himalaya. The earthquake had caused massive destruction across Assam and had even raised the bed of the river Brahmaputra, increasing impact of the annual flood in Assam.

The study was carried out by Wadia Institute of Himalayan Geology, Dehradun, an autonomous institute of the Department of Science and Technology, Government of India.

The research team led by Devajit Hazarika with the help of micro and moderate magnitude earthquakes in the region, recorded at the local seismological stations, emphasized the overall seismicity pattern in the Eastern Himalayas and adjoined IBR with special emphasis on the seismotectonic of the Lohit Valley region.

The study has been published in Tectonophysics Journal recently. The report was made public by the ministry of Science and Technology, New Delhi on Wednesday.

The Eastern Himalayan Syntaxis (EHS) in Arunachal Pradesh and bordering regions of Assam is acknowledged as one of the most seismically active regions in the world. The northeast corner of the Indian Plate in the EHS belongs to the seismic zone V of the national zoning map of India and does have a potential to trigger major earthquakes in the future.

In contrast to several studies carried out in the EHS and adjoining SE Tibetan plateau, extremely less studies have been done in the north-eastern fringe of the Indian Plate in the Eastern Himalayan Syntaxis (Tidding-Tuting Suture, TTSZ) for understanding seismogenesis and its tectonic linkage. After the 1950 great Assam earthquake, the region between the upper Assam and the Mishmi Block is not producing any large earthquakes and is considered as a seismic gap region, said the report.

Moderate magnitude earthquakes in the region are rarely reported by global seismological networks. To obtain information of moderate and microearthquakes, the Wadia Institu established 11 broadband seismological stations in the Lohit Valley and eight stations in the Siang Window of Arunachal Himalaya.

The study said that the TTSZ is seismically active up to around 40 km depth. In contrast, the seismicity in the Indo-Burma Ranges (IBR) is observed up to a depth of around 200 km suggesting the active subduction process of the Indian plate beneath the IBR. It suggests that the IBR is more susceptible to deeper earthquakes, while crustal-scale earthquakes are more likely to occur in the TTSZ.