Neotectonic Activities in Northern Saurashtra Peninsula Bordering Gulf of Kachchh

Abstract

This study points out the evidences of neotectonics and possible existence of active fault in northern part of Saurashtra Peninsula. The methodology used for the detection of neotectonism are: a) analysis of numerical data obtained from Digital Elevation Model (DEM) and its derivatives (morphometric indices), b) study of geomorphic markers and c) correlation of seismic & palaeoseismic data and geomorphology with structural lineaments. Morphometric indices such as drainage density, stream frequency, bifurcation ratio, basin length, basin relief, relief ratio, elongation ratio, stream gradient index, hypsometric index and sinuosity ratio have been used to assess the tectonic signatures. Morphometric indices suggest that Aji river basin is tectonically active, whereas Und and Sasoi river basins show some of the parameters in active tectonic range. Regional study using remotely sensed data (Landsat OLI multispectral) has helped to show a) about 100° dextral rotation of Aji river trunk channel near the Gulf coast and b) dextral deflection of both Aji and Und river about 25 km from the coast. Study of a segment of Aji river basin near Ranjitpura- Balamba proved upliftment and tilting of land resulting a) narrowing of trunk channel towards sea, b) development of new sets of channels over tilted river terrace, c) development of beheaded channels, d) presence of palaeo-channels and palaeo-delta in different directions with the present ones and e) formation of estuary with definite geometric shape. Occurrence of earthquake epicentres, in conformity with predicted lineaments in addition to paleoseismic records supports the existence of the fault. On the basis of integrated evidences it has been established that the Saurashtra coast along the Gulf of Kachchh is tectonically active with the existence of a dextral strike slip fault (ENE-WSW trending) with a rotational component manifesting tilting of the northern block towards east.