Evaluation of Historical Tectonic Imprints on the Subarnarekha River Basin, Eastern India and Its Impact on Longitudinal River Profile

Morphotectonic indices are beneficial for the determination of the intensity of tectonic activity (historical or ongoing) by quantifying the landscape geometry and other characteristics. The Subarnarekha River basin is an example of the Precambrian cratonic landscape of eastern India. The basin area contains several marks of historical tectonic imprints along with major waterfalls and slope breaks at the structural as well as lithological boundaries in the longitudinal course of the river. A set of morphotectonic indices, that is, asymmetry factor (Af), basin shape index (Bs), hypsometric integral (HI), stream length‐gradient index (SL), and valley floor width to valley height ratio (Vf) have been applied here for the identification of the intensity of historical tectonic imprints within the concerned region as these indices help to quantify the tectonic influences on a drainage basin. After combining all the indices, the basin has been classified into several classes in terms of the historical tectonic imprint intensity. The result shows that near about 35% of the sub‐basins (5 out of 14) are classified under high to very high historical tectonic imprint intensity zones. It is also identified that the upper basin area was relatively more tectonically active. The entire region is not facing any kind of ongoing tectonic activity, but there is numerous evidence of historical tectonic activity or imprints throughout the entire basin area. Longitudinal profiles of the streams indicate an abrupt slope change and the role of litho‐structural variation within the basin, and the entire basin area is also characterized by historical tectonic imprints and slow deformation rather than ongoing active tectonic activities. These tectonic imprints provide critical evidence for the reconstruction of the past geological history of the region.