Coulomb static stress variations in the Kachchh, Gujarat, India: Implications for the occurrences of two recent earthquakes in the 2001 Bhuj earthquake region

Abstract

S U M M A R YDouble difference algorithm was used to relocate aftershock sequences of two M w = 5.6 Kachchh earthquakes (India), which have occurred on 2006 March 7 and April 6, along almost vertical strike-slip Gedi fault (GF) and south dipping reverse North Wagad fault (NWF), respectively. The relocated focal depths delineate a marked variation of 4 and 7 km in the brittle-ductile transition depths beneath GF and NWF, respectively. We modelled the Coulomb failure stress change ( CFS) produced by the 2001 mainshock and 2006 GEDI events on an optimally oriented plane. A strong correlation with occurrences of aftershocks and regions of increased CFS is obtained on both the faults. The predicted CFS on the GF increased by 0.14 MPa at 3 km depth, where the 2006 March 7 M w = 5.6 event occurred. The variation in brittle-ductile transition depths may be related to the perturbation in geothermal gradient resulted from the presence of intrusives or varying saturation state of fluid-filled fractured rock matrix beneath both the fault zones.

Estimation of static stress changes after the 2001 Bhuj earthquake: Implications towards the northward spatial migration of the seismic activity in Kachchh, Gujarat

“…These are of remarkable diversity including right-lateral, leftlateral, oblique reverse, reverse, oblique normal, and normal faulting on planes sub-parallel or transverse to the south dipping NWF, which support the heterogeneous postseismic stress field hypothesis (Mandal and Horton, 2007). This continued aftershock activity triggered the neighbouring almost vertical Gedi fault (GF), 30 km north of NWF, in a strike-slip sense of motion that resulted in the occurrence of the 7 th March 2006 event of Mw 5.6 (hypocenter: 23.84 N,70.72 E, 3.0 km depth) (Mandal et al 2007a). It was followed on 6 April 2006 by Mw 5.6 event (hypocenter: 23.35 N,70.32 E, 28.2 km depth), which occurred along the NWF in a reverse sense of motion.…”

“…The receiver fault geometry of Antolik and Dreger (2003) for the Bhuj earthquake is adopted (strike = 82°, dip = 51°, rake = 77°). The receiver fault geometry for GF is considered to be a vertical strike-slip fault (strike = 90 o , dip = 78 o , rake = 178°) as obtained from the moment tensor analysis of the Bhuj aftershocks (Mandal et al 2007a), whereas, the ABF is assumed to be a north-dipping fault (strike = 270°, dip = 60°, rake = 170°) following Bilham (1999). For estimation of DCFS, we used the distributed slip model as obtained from the inversion of InSAR data where the majority of slip confines within a 20 km x 20 km region centered at a depth of 20 km (Schmidt and Burgmann, 2006).…”

Shallow subsurface imaging of the Wagad active fault system (Kachchh, northwestern India) by time domain electromagnetic studies

“…Recent studies suggest that the eastern Kachchh is a potential zone for major earthquakes in the near future (Biswas 2005;Rastogi et al 2012;Mandal 2016;Pavan Kumar et al 2017a, b). It is also evident from the concentration of earthquakes showing two prominent clustering around west and north of the Wagad region suggesting that this part of the basin is a highly strained zone with high seismic hazard potential (Mandal et al 2007;Mandal 2016;Pavan Kumar et al 2017a, b). The recognition and characterization of faults and its splays/branches in terms of geometry, type of movement and rates of activity are essential in understanding morphotectonics as well as assessing the seismic potential of a region.…”

“…Many geophysical and geological investigations have been carried out after the 2001 earthquake. The studies inferred re-activation and branching of existing faults in the region (Biswas and Khattri 2002;Mandal et al 2004Mandal et al , 2007Biswas 2005;Patidar et al 2007;Maurya et al 2013;Rastogi et al 2012, 1 2014), particularly in the eastern part of the KRB. The current aftershock activity has been attributed to activity along these fault systems.…”

“…Further, the study revealed the splaying nature of the fault in Quaternary sediments (Patidar et al 2008). Mandal et al (2004Mandal et al ( , 2007 on the basis of passive seismology studies, identified an E-W trending blind thrust, named as North Wagad Fault (NWF), which is suggested to be the causative fault for the 2001 Bhuj earthquake. A GPR study by Maurya et al (2013) infers that the Gedi fault (GF) is steep north dipping reverse fault, which becomes vertical at depth and is characterized by the moderate earthquake activity under a compressive stress regime.…”