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The Brahmaputra River flows through Assam, India, for about 670 km along an alluvial valley as a wide braided river. The width of the river varies with time along its course. The braiding intensity of this river is estimated using the braiding index (BI) of Brice (1964), which also changes with space and time along the course of the river. Temporal changes of both width and BI have been studied using topographic maps of 1912–1928 and 1963–1975, and dry season satellite data of 1996, 2000, 2007 and 2009. The mean widths of the Brahmaputra River channel in Assam during 1912–1928, 1963–1975, 1996, 2000, 2007 and 2009 were 5949 m, 7455 m, 7505 m, 8008 m, 8308 m and 9012 m, respectively, confirming an overall increase in width with time. Both the width and variation of width are lowest in four short narrower segments of the river. Three of these segments represent hard points comprising gneissic rock, and one segment is on alluvium comprising cohesive clay. The increase in width is correlated to enormous sediment load produced by the great Assam earthquake of 1950 and large-scale deforestation in the Himalayas. The mean BIs for the Brahmaputra for 1963–1975, 1996, 2000, 2007 and 2009 were 8.59, 8.43, 6.67, 6.58 and 7.70, respectively, indicating in general a decreasing trend up to 2007. The BI showed low variation at the four narrow segments where there is also a minimum variation of the channel width. The BI has increased significantly in the upstream part of the river. Very high fluctuation of discharge (17,000 m 3 / s − 1 in 24 h) and high sediment loads of the Brahmaputra (daily mean sediment discharge of 2.0 million tonnes during monsoon), erodible alluvial banks and high width/depth ratios are the main causes of development of braiding. The interrelationship between channel width and BI of the Brahmaputra shows a positive correlation, indicating an increase in BI with increasing channel width.

The Northeastern region (NER) of India is a seismically active region which lies in the most active zone V (BMTPC, 2003) (Figure 1a) of seismic zones of India. The region jawed in between the Himalayan collision arc to the north and northeast and the Indo Burmese subduction arc to the south and southeast has produced two great earthquakes (1897 and 1950) and the whole region experienced 20 large earthquakes (M > 7.0) during the last 200 years [Angelier and Baruah, 2009]. This region is tectonically divided into several mosaics by deep-rooted faults/thrust along which episodic block/thrust/strike-slip movements are reported [Nandy, 1986, 2001]. The seismicity pattern of NER shows relatively higher concentration of events in the Shillong and Mikir Plateaus, Arunachal Himalaya and Indo-Myanmar subduction zone. Amongst a number of active faults in NER, the Kopili and the Bomdila Faults are very active, which is evidenced from the occurrence of 24 large magnitude (M w ≥5.5) seismic events in recent past (Figure 1b). Concentration of events along both the Kopili and Bomdila Faults are considered to be an intraplate seismotectonic domain. These intraplate seismic activities are fairly intense in this region due to its complex stress regime [Nandy, 2001, Angelier and Baruah, 2009]. The Kopili Valley region has produced two large earthquakes Article history