Active Tectonic Deformation of the Kameng watershed: Evidence from Geomorphic Indices and Seismological Analysis

The north-eastern Himalaya display an early stage of tectonism since the disintegration of Gondwanaland. The Kameng watershed, situated in the westernmost part of the Arunachal Himalayas, represents a critical zone of active tectonic deformation. Its significance arises from its position at the triple junction of three major seismo-tectonic domains: the Eastern Himalayan Collision Zone (EHCZ) to the north, the Plate Boundary Zone of the Shillong Plateau Assam Valley Bengal Basin (PBZSPAVBB) to the southwest, and the Assam Gap (AG) to the southeast. Additionaly the region is traversed by four major fault and detachment systems: Main Frontal Thrust (MFT), Main Boundary Thrust (MBT), Main Central Thrust (MCT), and South Tibetan Detachment System (STDS) from south to north. Such geodynamic settings are expected to leave imprints on the spatial variability of tectonic activity across the region, making this an important aspect to investigate in understanding the differential tectonic response of the Kameng watershed. Concentrated earthquake events in the northwestern part of the watershed and a sudden debris flow in the recent past in Wapra-bung, a tributary located in the vicinity of the same region, drew significant attention and led to the hypothesis of a potential link among the ongoing stress accommodation along the older thrust and detachment systems (MCT and STDS) in the hinterland, the debris flow in the northwestern segment, and the concentrated distribution of seismic events in the northwest region of the Kameng watershed. Relative and Total Slope-extension Index (RDEs/RDEt), the Stream Length Gradient–Hotspot and Cluster Analysis (SL-HCA) using the Getis-Ord Gi statistic, Relative Tectonic Uplift (Ut) of the sub-watersheds, along with seismological analysis using the Gutenberg–Richter relationship, were conducted on seventeen sub-watersheds of the Kameng watershed to evaluate tectonic deformation within the region. Findings suggest that the heightened tectonic activity in the northwestern region is not coincidental but is likely linked to the Radial Expansion and the Oblique Convergence Model, with ongoing stress accommodation along the STDS and MCT in the hinterland. In contrast, the eastern side of the Kameng watershed exhibits lower seismic activity and reduced tectonic instability, possibly associated with the Assam Gap, where the stress release rate is relatively low compared to the Eastern Himalayan Collision Zone to the north and the Shillong Plateau to the southwest. In Arunachal Himalaya, approximately 6 mm/yr of total ~15 mm/yr plate convergence is being absorbed between Bomdila and Tezpur in the Lesser/Outer Himalaya; this fact could be the explanation of the heightened tectonic activities. In comparison, about 10 mm/yr is taken up between Bomdila and Tawang in the Greater/Tethyan Himalaya. Field evidence, including a 39°C hot water spring near Dirang along the Bichom River, further supports the inference of active deformation within the north-western side of the watershed.