NEOTECTONIC EVOLUTION OF ACTIVE FAULTS IN THE INTRACRATONIC KACHCHH PALAEO-RIFT BASIN, WESTERN INDIA USING FIELD AND GPR DATA

The E-W trending intrabasinal faults of the seismically active Kachchh palaeorift basin are characterized by the presence of a narrow flexure zone consisting of domes and anticlines on the upthrown side. All faults have prominent geomorphological expression and qualify to be categorised as active as indicated by available data and distribution of earthquakes that have occurred during historic time. The present study is based on extensive field and Ground Penetrating Radar (GPR) studies along the Kachchh Mainland Fault (KMF), Gedi Fault (GF) and the South Wagad Fault (SWF). The study was aimed at precise mapping of the hear surface trace of the faults, their shallow subsurface nature and neotectonic history. Lithostratigraphy of the Quaternary deposits overlapping the fault zones was also reconstructed. All faults investigated in the present study, are marked by the contact between Mesozoic rocks and Tertiary rocks which is easily picked up and interpreted in the processed GPR profiles by visible change in the pattern of reflectors. At places, where the fault trace was covered by colluvio-fluvial deposits and aeolian miliolite, these deposits were also imaged in the processed GPR profiles as an undeformed mass of reflectors overlying the reflectors of Mesozoic and Tertiary rocks. The Quaternary sediments of the KMF zone show three major neotectonically controlled aggradation phases. The GPR studies suggest that the KMF is near vertical northward steeply dipping fault that tends to become a steep south dipping reverse fault in the vicinity of transverse faults. The GPR data of SWF shows that the fault is a steep southward dipping fault. GPR profiles taken in the Gedi Fault (GF) zone indicates that the fault is steeply north dipping reverse fault near the surface that becomes vertical at depth. The integrated approach of GPR surveys and field studies suggest a dominantly N-S oriented compressional stress environment along the KMF, SWF and GF. However, the segmented nature and change in the behavior of the faults in different segments indicates that the distribution, accommodation and release of stresses are not uniform along the faults.