Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

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Estimation of Static Stress Changes after the 2001 Bhuj Earthquake: Implications towards the Northward Spatial Migration of the Seismic Activity in Kachchh, Gujarat


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1 National Geophysical Research Institute (Council of Scientific and Industrial Research), Uppal Road, Hyderabad - 500 606, India
     

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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 7th March 2006 Mw5.6 event occurred, whereas predicted DCFS on the ABF increased by 0.07 MPa at 30 km depth, where the 15th 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.

Keywords

Migration of Seismicity, Aftershocks, Focal Mechanisms, Kachchh Seismic Zone, Intraplate Earthquakes, Gujarat.
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  • Estimation of Static Stress Changes after the 2001 Bhuj Earthquake: Implications towards the Northward Spatial Migration of the Seismic Activity in Kachchh, Gujarat

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Authors

Prantik Mandal
National Geophysical Research Institute (Council of Scientific and Industrial Research), Uppal Road, Hyderabad - 500 606, India

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 7th March 2006 Mw5.6 event occurred, whereas predicted DCFS on the ABF increased by 0.07 MPa at 30 km depth, where the 15th 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.

Keywords


Migration of Seismicity, Aftershocks, Focal Mechanisms, Kachchh Seismic Zone, Intraplate Earthquakes, Gujarat.

References