Significance of neotectonics in assessing the relative tectonic activity in and around the Mat Fault of Eastern Himalayan Fold Belt, Mizoram, north‐east India

Abstract

The Mat Fault situated in the Eastern Himalayan Fold Belt was mapped around Mizoram and is oriented NNW to SSE. This region has experienced a number of earthquakes in the recent past that damaged settlements and triggered numerous landslides. A set of geomorphic parameters were analysed on both sides of the Mat Fault to understand the tectonic setting. The six geomorphic parameters include: elongation ratio, hypsometric analysis, asymmetry factor, transverse topographic symmetry factor, stream length‐gradient index, and valley floor‐to‐width ratio, and they were calculated for 20 fourth‐order sub‐watersheds. Out of 20 sub‐watersheds, 10 sub‐watersheds were selected from the northern block and 10 from the southern block. Hypsometric analyses show that all the sub‐watersheds have attained a mature stage of geomorphic cycle of erosion; and from the analysis of hypsometric curves, it is found that 16 of the sub‐watersheds might have been uplifted due to tectonic activity. The asymmetry and transverse topographic symmetry factor values also suggest tilting in different directions possibly due to obstruction by faulting. The anomaly of high stream length index values is also observed in different sub‐watersheds indicating neotectonic activity. Low values of the valley floor‐to‐width ratio (<0.5) suggest V‐shaped valley topography, which indicate vertical incision due to tectonic activity. On evaluating relative tectonic activity among 20 sub‐watersheds, it is found that 80% of sub‐watersheds in the northern block show relatively stronger tectonic activity than the southern block. The present work suggests that the study area is tectonically active, and the possibility that they were produced by seismic activity.