Deep crustal electromagnetic structure of Bhuj earthquake region (India) and its implications
Naganjaneyulu, K. (National Geophysical Research Institute, Council of Scientific and Industrial research (CSIR))
Ledo, Juan José (Universitat de Barcelona. Departament de Geodinàmica i Geofísica)
Queralt, Pilar (Universitat de Barcelona. Departament de Geodinàmica i Geofísica)

Data:	2010
Resum:	The existence of fluids and partial melt in the lower crust of the seismically active Kutch rift basin (on the western continental margin of India) owing to underplating has been proposed in previous geological and geophysical studies. This hypothesis is examined using magnetotelluric (MT) data acquired at 23 stations along two profiles across Kutch Mainland Uplift and Wagad Uplift. A detailed upper crustal structure is also presented using twodimensional inversion of MT data in the Bhuj earthquake (2001) area. The prominent boundaries of reflection in the upper crust at 5, 10 and 20 km obtained in previous seismic reflection profiles correlate with conductive structures in our models. The MT study reveals 1-2 km thick Mesozoic sediments under the Deccan trap cover. The Deccan trap thickness in this region varies from a few meters to 1. 5 km. The basement is shallow on the northern side compared to the south and is in good agreement with geological models as well as drilling information. The models for these profiles indicate that the thickness of sediments would further increase southwards into the Gula of Kutch. Significant findings of the present study indicate 1) the hypocentre region of the earthquake is devoid of fluids, 2) absence of melt (that is emplaced during rifting as suggested from the passive seismological studies) in the lower crust and 3) a low resistive zone in the depth range of 5-20 km. The present MT study rules out fluids and melt (magma) as the causative factors that triggered the Bhuj earthquake. The estimated porosity value of 0. 02% Hill explain 100-500 ohm•m resistivity values observed in the lower crust. Based on the seismic velocities and geochemical studies, presence of garnet is inferred. The lower crust consists of basalts - probably generated by partial melting of metasomatised garnet peridotite at beeper depths in the lithosphere - and their composition might be modified by reaction with the spinel peridotites.
Drets:	Aquest document està subjecte a una llicència d'ús Creative Commons. Es permet la reproducció total o parcial, la distribució, la comunicació pública de l'obra i la creació d'obres derivades, fins i tot amb finalitats comercials, sempre i quan aquestes es distribueixin sota la mateixa llicència que regula l'obra original i es reconegui l'autoria de l'obra original.
Llengua:	Anglès
Document:	Article ; recerca ; Versió publicada
Matèria:	Electrical resistivity ; Mesozoic sediments ; Fluids ; Bhuj earthquake ; Intraplate seismicity
Publicat a:	Geologica acta, Vol. 8, Núm. 1 (Març 2010) , p. 83-97, ISSN 1696-5728

Adreça alternativa: https://raco.cat/index.php/GeologicaActa/article/view/188006
Adreça alternativa: https://revistes.ub.edu/index.php/GEOACTA/article/view/1943
DOI: 10.1344/105.000001517

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