Acta Geodaetica et Geophysica Hungarica
Volume/Issue:
Volume 42: Issue 3
Upper mantle instability and seismic activity of Kutch and adjoining areas with special reference to Bhuj earthquake of 2001, Gujarat, India — A petrologic model
Authors:
V. Singh Banaras Hindu University Department of Geophysics Varanasi India

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D. Shanker Indian Institute of Technology Roorkee Department of Earthquake Engineering 247667 Roorkee, Uttaranchal India

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H. Singh Banaras Hindu University Department of Geophysics Varanasi India

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M. Banerjee Banaras Hindu University Department of Geophysics Varanasi India

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Pages:
323–340
Online Publication Date:
31 Jul 2007
Publication Date:
01 Sep 2007
Article Category:
Journal Article
DOI:
https://doi.org/10.1556/ageod.42.2007.3.6
Keywords:
Bouguer gravity anomalies; fluid incursion; Peninsular Shield; petrologic modeling; subsidence rates
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Seismically Kutch peninsula is very active. The distribution of seismicity in Peninsular Shield region from 1902 to 2001 show 12 earthquakes of M ≥ 6. The energy ratio from Kutch basin to Deccan trap is 20:1 and from trap to rest of the shield is 5:1. The last one hundred years seismicity data show Kutch basin is seismically more active than Deccan trap and the rest of the Peninsular Shield. The maximum magnitude of earthquake in the Kutch region is 7.7. The generations of large earthquakes in the region are difficult to explain, as plate boundary does not exist. In order to understand the physical processes that are taking place in the region to generate such large events the detailed analyses of geophysical and geological data have been examined in the light of development of rift, subsidence of basin, vertical tectonics and recent geophysical findings. In such regions, petrologic model can provide better explanation for release of fluid that generates large earthquakes, sprouting of sands, liquefaction, and large number of aftershocks activities and direction of stresses for aftershock sequences. The presence of magma in the Kutch upper mantle could be derived from various geological (subsidence of basin, development of rift faults) and geophysical observations (high heat flow over Cambay region, prominent positive Bouguer gravity anomalies and low shear velocity in the upper mantle). The inspection of seismological data shows all the medium size to large earthquake have occurred in shear zone of large gravity gradients or along the four major faults of the region. In view of geological and geophysical observations, petrologic model is proposed for generation of earthquakes in the region. The number of aftershocks and direction of stresses in the focal region of aftershocks would depend on the direction of movement of fluid incursion in the focal region after the occurrence of the main events. The recent Bhuj earthquake also shows more than 3000 aftershocks from Jan 29 to April 15, 2001. The expanding swarm activity in the focal region and the direction of stresses derived from first motion data of aftershocks for focal depths 2 to 8 km, 8 to 25 km, and 25 to 38 km supports the proposed model. Also, shear wave tomography studies in this region have revealed low shear wave velocity in the upper mantle of Cambay from shallow depth to 200 km depth showing high temperature zone. The analyses reveal the presence of conducting fluid in the focal zone, which is the main cause for generation of medium size to large earthquake in the region.

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Cover Acta Geodaetica et Geophysica Hungarica
Acta Geodaetica et Geophysica Hungarica
Print ISSN:
1217-8977
Online ISSN:
1587-1037

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Acta Geodaetica et Geophysica
Language English
Size B5
Year of
Foundation		 2013
Volumes
per Year		 1
Issues
per Year		 4
Founder Magyar Tudományos Akadémia
Founder's
Address		 H-1051 Budapest, Hungary, Széchenyi István tér 9.
Publisher Akadémiai Kiadó Springer
Nature Switzerland AG
Publisher's
Address		 H-1117 Budapest, Hungary 1516 Budapest, PO Box 245.
CH-6330 Cham, Switzerland Gewerbestrasse 11.
Responsible
Publisher		 Chief Executive Officer, Akadémiai Kiadó
ISSN 2213-5812 (Print)
ISSN 2213-5820 (Online)

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