Neotectonics assessment using geomorphic indices: A study from the passive continental margin of India

The response of landforms to tectonic deformative processes can be effectively understood by using geomorphic indices. The objective of this study is to evaluate the extent of neotectonic activities in the fourth-order sub-basins of a tropical river basin (Kallada River basin) in the Southern Granulite TerrainIndia. The extend of neotectonism was analyzed using geomorphic indices such as asymmetry factor, transverse topographic symmetry factor, hypsometric integral, stream-length gradient index, drainage basin shape index, ratio of valley floor to valley height, and mountain front sinuosity, with values varying from 0.3 to 41.20, 0.12 to 0.54, 0.13 to 0.69, 12.76 to 1036.49, 0.63 to 3.81, 0.05 to 6.04, and from 1.02 to 3.08, respectively. Further, the relative active tectonics index (IRAT) was derived from the geomorphic indices using GIS and the values vary from 1.67 to 3.0. Based on the degree of relative tectonic activity, Kallada River basin was classified into class 1, 2, 3 and 4 corresponding to very high (1.0-1.5), high (1.5-2), moderate (2.0-2.5), and low (IRAT>2.5) values. The spatial distribution of different “IRAT” classes shows a gradational pattern from east to west, suggesting a gradual decrease in the neotectonic activity in the basin.