Geomorphic response to neotectonic instability in the Deccan volcanic province, Shetrunji River, western India: Insights from quantitative geomorphology

Abstract

The Saurashtra peninsula, a Deccan Trap terrain, in western India lacks the studies that document on-land information of tectonically active faults. In the present paper, the tectonogeomorphology of the Shetrunji River basin is investigated to identify the neotectonic signatures of the buried structural element by detailed analyses of the landforms and drainage pattern using quantitative geomorphic analysis, morphostructural studies and Gradient length analysis (GLA) along with field investigation. The basin has been divided into three segments based on channel orientation, (a) Segment-1 (upper reach): oriented in NE-SW direction (b) Segment-2 (middle reach): oriented in an E-W direction and (c) Segment-3 (lower reach): oriented in NW-SE direction. The tectono-geomorphic analysis suggests the neotectonic deformation is mainly demonstrated by the NE-SW oriented Girnar Fault (GF) in Segment-1 and E-W oriented Shetrunji Fault (SF) in Segment-2. The Segment-3 interestingly shows least or no tectonic deformation signatures. For the first time, we report the geomorphic evidence of the two main faults 1) the Girnar Fault (GF) ~ a left-lateral strike slip fault and 2) the Shetrunji Fault zone (SFz) ~ a right-lateral strike slip fault. The interplay between drainage pattern and buried structures are observed in the form of offset channel/offset ridges, deflection in stream and linear valleys. The SFz is characterized by an anastomosing drainage pattern, offsetting/deflection of streams and development of linear valleys in zone which is 52 km in length and 2 km wide. The SL index and Ksn show high values along the fault zone, which is also, supported by the presence of incised river channel, entrenched mender and incised ravine surfaces. The study reveals the prevalent neotectonic activity in the Shetrunji River basin along with the GF and the SFz. The findings are consistent with the geomorphic - structural setup of the region, and coincide with the historical as well as current seismicity distribution.