Delineation of tectonically active zones in the Island Belt Uplift region, Kachchh Basin, western India: A geomorphic and geodetic approach

Abstract

In the present study, we have identified the tectonically active zones along the Island Belt Uplift (IBU), an upthrown block of E-W trending Island Belt Fault (IBF). Major and minor transverse faults have segmented the IBU into four sub-uplifts, viz. Pachham Uplift (PU), Khadir Uplift (KU), Bela Uplift (BU), and Chorar Uplift (CU) from west to east, respectively. The work includes geodetic and morphotectonic analysis of the IBU region. The Normalized Steepness Index (Ksn) analysis was performed supported by swath profiling to mark the tectonic activity variations along and across the strike of the IBF in the IBU region. Further, the Ksn contour map was prepared by using a power-law function of slope (S) of the longitudinal profiles of the river, concavity index (ө), and upstream area (A), which is an integral part of the Stream Power Incision Model (SPIM). The Ksn analysis suggests that the maximum amount of tectonic activity is restricted along the northern escarpment of the IBU, which falls in the vicinity of IBF and it's associated longitudinal and transverse faults. Based on the results of Ksn analysis, we have marked the tectonically active zones in the IBU region, which shows that amongst four sub-uplifts, the PU and BU were found most active (Zone-I), the KU expresses moderate activity (Zone-II), while CU demonstrated to be least active (Zone-III). The results were also confirmed by documentation of active tectono-geomorphic features like strath terraces, river offsets, straight fault scarps, triangular facets, linear valleys, fault ridges, Quaternary upwarps, laterally displaced crests and alluvial fans within the IBU. The active deformation pattern calculated using the Global Positioning System (GPS) data-set from 2009–2019 along IBU reveal maximum deformation rate of ∼2.5 ± 0.5 mm/yr in the PU, ∼2.0 ± 0.5 mm/yr in the BU while, the KU shows the deformation rate of ∼1.2 ± 0.5 mm/yr, which coincides well with the results of Ksn. The Ksn analysis results were also validated by comparing them with existing Gradient Length Anomaly (GLA) and Differential Interferometric Synthetic Aperture Radar (DInSAR) data. The ongoing tectonic activity in the study area is also manifested by the occurrence of moderate seismic activities in the identified active zones. The active tectono-geomorphic features and fault scarp geometry were analyzed and compared with the existing experimental models of basement fault and overlying sedimentary covers, which allow us to understand the nature of fault components of IBF. The analysis reveals that the IBF has been influenced by both dip-slip and strike-slip fault components of motion, which can be further confirmed by geophysical analysis. The results of Ksn analysis and field evidence were merged to prepare Active Fault Map of the IBU region that can be implemented for future seismic hazard assessment.

Keywords

• Island belt uplift
• Ksn analysis
• Active fault map
• Island belt fault
• Seismic hazard assessment