Geomorphic signatures in relation with seismo-tectonic studies of Kameng watershed, NE Himalaya

Abstract: The Kameng watershed, Arunachal Pradesh, is a region uniquely positioned at the
confluence of distinct seismo-tectonic zones: the Eastern Himalayan Collision Zone to the
north, the Shillong Plateau to the southwest, and the Assam Gap (an aseismic corridor) to the

southeast, each zone characterized by varying strain accumulation and release. The primary

focus of the study is to assess how these distinct seismic zones, with their differing stress and

strain characteristics, contribute to seismo-tectonic differences on the eastern and western

sides of the Kameng watershed. Utilizing morphometric parameters such as sinuosity index,

stream length gradient index, and concavity index, alongside seismo-tectonic methods like b-

value analysis and Space-Time-Depth-Magnitude (STDM) analysis, degrees of tectonic

activity in sub-watersheds were identified. Tectonic-induced Knickpoints were extracted

using the RDEs/RDEt index and clustering method used to quantify the active stretches. Sub-

watersheds on the western side, particularly the Wapra Bung (SW-9) and Pachuk (SW-10)

rivers, demonstrate higher tectonic activity. This heightened activity is attributed to the

crossing of major tectonic features like the South Tibetan Detachment (STD) and Main

Central Thrust (MCT). GPS-inferred studies indicate maximum strain rates of 6-8×10⁻⁷ strain/year with deformation rates of ~15mm/year near the MCT and ~7mm/ year near STDS in the Lesser Himalaya, further supporting the high tectonic strain in these areas. Over the past decade, seismic records reveal an increase in earthquake frequency, especially in the northern sections of SW-9 and SW-10, with numerous events of magnitude <5.7. This increase in seismicity aligns with significant geomorphic changes, such as the debris flow in the Wapra Bung River in 2021, which was likely triggered by a combination of seismic activity, and freeze-thaw cycles. The findings underscore the tectonic and seismic instability of the region, which contribute to periodic avalanches and debris flows.