Spatial variations in tectonic activity along the Kachchh Mainland Fault, Kachchh, western India: implications in seismic hazard assessment

The landscape of Kachchh is a unique example of active intraplate region in the world. Various structural features such as domes, faults, folds and associated intrusive suggest early tertiary tectonic history, while youthful topography like youthful nature of the fault scarps and gorges suggests Quaternary tectonic history. Kachchh Mainland Fault (KMF) is a 170-km-long E-W-oriented south-dipping reverse fault situated in pericratonic Mesozoic rift basin in western India. The KMF is a neotectonically active fault substantiated by distinct tectonic geomorphology and seismotectonic history. As Kachchh region experiences an arid climate, it lacks vegetation and provides favorable conditions for assessing the morphology of mountain fronts and gradient of channels using remote sensing to evaluate the relative tectonic activity. We employed the means of quantitative geomorphic analysis extracted from a DEM to access the spatial variation in tectonic activity. The assessment of geomorphic indicators of active tectonics was carried out using tectono-geomorphic parameters such as stream length-gradient index (SL index), mountain front sinuosity (S (mf)) and valley floor width-height ratio (V (f)). These parameters were combined to generate the relative index of active tectonics (RIAT) which was further divided into four classes as per degree of tectonic activity. The RIAT classes show segmented nature of KMF, with four segments having decrease in degree of tectonic activity from east toward west. The central and the eastern segments of KMF fall in class 1 and class 2 of RIAT, indicating a relatively higher degree of recent tectonic activity undergone by them. The results of geomorphic analysis are consistent with the landforms present, geological setup and seismicity in the study area. The study would be helpful in accessing the regional seismic hazard from KMF for the entire western India.