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

Abstract

Spatial-temporal patterns of aftershocks of the 2001 Mw7.7 Bhuj earthquake during 2001-2008 reveal a northward spatial migration of seismic activity in the Kachchh seismic zone, which could be related with the loading stresses caused by the continued occurrences of aftershocks on the north Wagad fault (NWF), the causative fault of the 2001-mainshock. Aiming at explaining the observed northward migration of activity, we modelled the Coulomb failure stress change (DCFS) produced by the 2001-mainshock, the 2006 Mw5.6 Gedi fault (GF) and the 2007 Mw4.5 Allah bund fault (ABF) events on optimally oriented plane. A strong correlation between occurrences of earthquakes and regions of increased DCFS is obtained on the associated three faults i.e. NWF, ABF and GF. Predicted DCFS on the GF increased by 0.9 MPa at 3 km depth, where the 7 th March 2006 Mw5.6 event occurred, whereas predicted DCFS on the ABF increased by 0.07 MPa at 30 km depth, where the 15 th December 2007 Mw4.5 event occurred. Focal mechanism solutions of three events on the ABF have been estimated using the iterative inversion of broadband data from 5-10 stations, which are also constrained by the first P-motion data from 8-12 stations. These focal mechanism solutions for the ABF events reveal a dominant reverse movement with a strike-slip component along a preferred northwest or northeast dipping plane (~50-70°). Focal mechanisms of the events on all the three fault zones reveal an N-S oriented P-axis or maximum principal stress in the region, which agrees with the prevailing N-S compression over the Indian plate. It is apparent that the northward migration of the static stress changes from the NWF, resulting from the occurrence 2001 Bhuj mainshock, might have caused the occurrence of the events on the GF and ABF during 2006-08.

Unravelling the Hidden Truth from Vigukot in the Great Rann of Kachchh, Western India by Surface and Sub-Surface Mapping

“…The 1845 earthquake (M w > 7) resulted in the flooding of Kori river and also uplifted Sunda area by 1 m located about 40 km south of Allah Bund [17][18][19] . The 1956 Anjar earthquake (M w 6.1) was a moderate magnitude event that occurred during post-instrumentation period with no surface rupture reported 20 . One of the most damaging intraplate earthquakes was experienced on 26 January 2001 (M w 7.6) that occurred in the failed rift of Kachchh on a blind thrust and resulted in vast destruction and casualties ( Figure 1 …”

Stochastic finite fault modelling of M w 4.8 earthquake in Kachchh, Gujarat, India

“…The region is seismically active and experienced two large earthquakes (M w 7.8, 1819, Kachchh and M w 7.6, 2001, Bhuj) within 200 years, besides several moderate size earthquakes (Johnston 1994;Rajendran and Rajendran 2001). The aftershock activity of 2001 Bhuj earthquake is still continuing (Mandal 2009). The Institute of Seismological Research has installed a network of 50 strong motion accelerographs in the Gujarat region.…”

Evidence for a fluid flow triggered spatio-temporal migration of seismicity in the 2001 Mw 7.7 Bhuj earthquake region, Gujarat, India, during 2001–2013

“…The migration of seismicity observed during the 1997 Umbria-Marche (Italy) earthquake has been explained successfully through diffusion of a porepressure perturbation (generated by the coseismic stress changes associated with the mainshock) in a poro-elastic, fluid-saturated medium (Antonioli et al 2005). In Kachchh, the occurrences of three earthquakes (viz., M w 7.7 2001 mainshock, and M w 5.6 2005 and M w 4.9 2010 Kachchh events) have been related to the triggering through static stress changes (To et al 2006;Mandal 2009a). But, the seismicity pattern reveals that seismicity migrated to and activated both the Gedi and Allah-Bund faults in Kachchh, Gujarat, India, before the occurrences of impending mainshocks Mandal 2009a).…”

“…In Kachchh, the occurrences of three earthquakes (viz., M w 7.7 2001 mainshock, and M w 5.6 2005 and M w 4.9 2010 Kachchh events) have been related to the triggering through static stress changes (To et al 2006;Mandal 2009a). But, the seismicity pattern reveals that seismicity migrated to and activated both the Gedi and Allah-Bund faults in Kachchh, Gujarat, India, before the occurrences of impending mainshocks Mandal 2009a). Now, if we assume that the co-and post-seismic stress changes associated with the 2001 mainshock have promoted fluid flow in the aftershock zone, facilitating the migration of seismicity, then, it would be important to reinterpret the model of observed migration in Kachchh seismicity in terms of fluid flow and pore-pressure relaxation.…”