S. Mukhopadhyay IIT Roorkee Department of Earth Sciences Roorkee 247667 India

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J. Kayal 73/B Thakurpukur Road Kolkata 700 063 India

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More than 5000 high precision seismic phases of 560 selected aftershocks ( M ≥ 2.0) of the January 26, 2001 Bhuj earthquake ( MW 7.7) in western India are used for joint determination of the hypocentral parameters and for 3D inversion of P-wave velocity and Vp / Vs structures in the source area. The aftershocks are located with an average rms of 0.19 s, and average error estimates of latitude, longitude and depth are 1.2, 1.1 and 2.3 km respectively. Most of the aftershocks occurred in an area 70 × 35 sq km; the intense activity was observed at a depth range 12–37 km. A bimodal distribution of aftershocks indicates that the main shock rupture propagated in upward and downward directions. Further, the best located aftershocks show two trends, one in northeast, parallel to Anjar Rapar Lineament, and the other in northwest parallel to the Bhachau Lineament. Fault-plane solutions of the northeast trending aftershocks indicate reverse faulting with left-lateral strike-slip component. These solutions are comparable with the main shock solution. The northwest trending aftershocks, on the other hand, show reverse faulting with right-lateral strike-slip motion. The estimated velocity structure indicates that the source zone of the Bhuj earthquake has a number of blocks showing lateral heterogeneities in P-and S-wave velocities. A block having higher P-and S-wave velocities appears to have uplift relative to its surroundings. The mainshock occurred at the boundary between the high Vp , high Vs uplifted block and the adjacent low Vp , low Vs block. Gravity observations support our 3D inversion results. This high velocity block is surrounded by rocks of higher Vp / Vs or lower rigidity, which possibly acted as a barrier zone.

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

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