Search

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. [ABSTRACT FROM AUTHOR]

We describe a study of the E-W-trending SouthWagad Fault (SWF) complex at the eastern part of the Kachchh Rift Basin (KRB) in Western India. This basin was filled during Late Cretaceous time, and is presently undergoing tectonic inversion. During the late stage of the inversion cycle, all the principal rift faults were reactivated as transpressional strike-slip faults. The SWF complex shows wrench geometry of an anastomosing en échelon fault, where contractional and extensional segments and offsets alternate along the Principal Deformation Zone (PDZ). Geometric analysis of different segments of the SWF shows that several conjugate faults, which are a combination of R synthetic and R' antithetic, propagate at a short distance along the PDZ and interact, generating significant fault slip partitioning. Surface morphology of the fault zone revealed three deformation zones: a 500 m to 1 km wide single fault zone; a 5-6 km wide double fault zone; and a c. 500 m wide diffuse fault zone. The single fault zone is represented by a higher stress accumulation which is located close to the epicentre of the 2001 Bhuj earthquake of Mw 7.7. The double fault zone represents moderate stress at releasing bends bounded by two fault branches. The diffuse fault zone represents a low-stress zone where several fault branches join together. Our findings are well corroborated with the available geological and seismological data. [ABSTRACT FROM AUTHOR]

This study presents results of microtremor analysis carried out over diverse geological formations and liquefaction sites in the Kachchh seismic zone of western India, which is host to the deadliest intraplate earthquake (Mw 7.7). Microtremors were recorded at 36 sites with single stations and 7 sites with an array. The microtremor array measurements were made using triangular arrays with sensors kept at 30-90 m radii. The Rayleigh-wave velocities are estimated from the array data using high-resolution frequency-wavenumber (f-k) analysis, and the 1D shear-wave velocity structure is determined by inversion. We found a good correlation between surface geology, resonant frequency and amplitude of the horizontal-to-vertical spectral ratio (HVSR) curve, and shear-wave velocity. The ground vulnerability index (Kg) values in the liquefied areas are found to be higher than those in the adjacent areas devoid of liquefaction. Broad or multiple peaks in the HVSR curves and large variations in the shear-velocity models could be attributable to the structural and tectonic complexity in the maximum intensity area. Further, our results show that the average fundamental frequencies are around 0.32 Hz for the Quaternary, 0.80 Hz for Tertiary, 1.8 Hz for Cretaceous, 1.8 Hz for Jurassic, and 2.3 Hz for the Deccan trap formations. The inverted S-wave velocity varies from 190 to 1350 m/s down to a depth of 200 m for the Quaternary, 220 to 680 m/s down to 100 m for Tertiary, 236 to 1160 m/s for Cretaceous, 670 to 1780 m/s for Jurassic, and 260 to 2440 m/s for the Deccan trap sites. The results of microtremor analysis corroborate the observations from the available geophysical, geological, and borehole data. [ABSTRACT FROM AUTHOR]

A correction to the article "Terrain response to the 1819 Allah Bund earthquake in western Great Rann of Kachchh, Gujarat, India" that was published in the 2012 issue is presented.