Bed parallel slip and paleostress analysis of the Kodki fault zone, Kachchh, Western India

The Kodki fault zone comprises a unique fault system along the Median High (MH) zone in the Kachchh Mainland Uplift (KMU) region of the Kachchh Rift Basin (KRB). The structural and paleostress investigation of the Kodki fault zone shows a typical style of bed-parallel slip (BPS) due to repeated reactivation of the normal faults. The fault growth is accompanied by the reactivation of one or both of the fault segments followed by offset due to BSP. In sections where both fault planes reactivate, and propagate past one other forms a bulk between coinciding fault segments that display typical characterization of relay zones. These structures in the Kodki fault section differ from the conventional relay zone in the strata. The thickness of BPS surfaces along the strata equals the fault's throw at the time of the BPS event. Geometrical restoration of the Mesozoic cross-sections exposed across the selected fault displays repeated BPS forming a complex intersecting structure along the Kodki fault zone. Further, the paleostress analysis determines E-W to WNW-ESE maximum extensional stress inhibits recurrences from the reactivation of faults with the MH zone

Estimation of regional surface deformation post the 2001 Bhuj earthquake in the Kachchh region, Western India using RADAR interferometry

The key objective of the present study is to estimate the surface displacement and to understand/monitor the active deformation pattern in the Kachchh region post the 2001 Bhuj Earthquake by implementing the Persistent Scatterer Interferometric Synthetic Aperture Radar (PSI) and Differential Interferometric Synthetic Aperture Radar (DInSAR) techniques. We employed the ENVISAT ASAR (15 images), ALOS PALSAR (6 pairs) and SENTINEL-1A (117 images) data sets acquired during the periods 2003–2005, 2007–2009, and 2016–2020 respectively. The PSI results of the Envisat dataset reveals that the Kachchh mainland region has undergone an average surface deformation of ± 22 mm/yr during 2003–2005. The maximum displacement observed from the ALOS PALSAR data sets (Window-1 to 6) during the period 2007–2009 is ∼ ± 1.2 cm. Further, the ground displacement observed from the Sentinel-1A dataset during the period 2016–2020 is ±16 mm/yr for the west-central region and 6 mm/yr uplift and 8 mm/yr subsidence in the eastern Kachchh mainland region. Surprisingly, high rate of deformation is detected towards the Pachham Island, Banni, Rann and the eastern region of the Kachchh after the 2001 Bhuj event. Correlating the results of different data sets, it is concluded that the deformation is high near the vicinity of the fault zones indicating the tectonically active nature of the faults. From the obtained results, we infer that, post the 2001 Bhuj earthquake, the surface displacement in the Kachchh mainland region is escalated till 2009 which is due to continuous aftershock activity and then started declining because of the ongoing seismic settlement. The acquired deformation rates are correlating well with the GPS derived displacement rates. Further, our results will assist in accurately demarcating the extent of the fault zones and also helps in precisely marking the areas undergoing active deformation, which will aid in micro zonation studies, mitigation planning and also for the preparation of an active tectonic map for the region

Structural analysis and neotectonic evidences of the dip-slip transverse fault system in the central Mainland Kachchh region, Western India

The spatio-temporal changes in the fluvial system and landform of the central Kachchh Mainland region are caused by distinctive ongoing tectonic deformations. The present study aims to decipher ongoing tectonic processes resulting modification of landscape in the Central Mainland Kachchh region during the Late Quaternary period. The region marks the presence of several neotectonic features along the faults indicating rejuvenation of the landform due to tectonic activity. The paleostress analysis of the faults indicates normal faulting due to WNW-ESE, E-W to WSW-ENE directed radial to pure extension. The OSL dates from the strath terrace section confirm accommodation of Quaternary sediments from ∼42ka till ∼32ka. The presence of abandoned channels and obstructed tributary channels across the fault plane deciphers reactivation of extensional fault planes at ∼42ka, constituting accommodation space for sedimentation on the downthrown block forming several sag-fill deposits. The sedimentation ceased after ∼32ka due to regional Kachchh Mainland Uplift (KMU) upliftment triggering vertical incision of channels forming several strath and fluvial terraces. The paleostress analysis and dynamic modification of landform depict reactivation of the hinge faults on the structural Mesozoic bend of the basement high known as the ‘Median High’