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Acta Geodaetica et Geophysica Hungarica

, Volume 43, Issue 1, pp 75–92 | Cite as

The 2001 Bhuj earthquake (M W7.7) in western India: 3D velocity structure and seismotectonic processes

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Abstract

More than 5000 high precision seismic phases of 560 selected aftershocks (M ≥ 2.0) of the January 26, 2001 Bhuj earthquake (M W 7.7) in western India are used for joint determination of the hypocentral parameters and for 3D inversion of P-wave velocity and V p/V s 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 V p, high V s uplifted block and the adjacent low V p, low V s block. Gravity observations support our 3D inversion results. This high velocity block is surrounded by rocks of higher V p/V s or lower rigidity, which possibly acted as a barrier zone.

Keywords

asperity barrier Bhuj block tectonics local earthquake tomography 

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Copyright information

© Akadémiai Kiadó 2008

Authors and Affiliations

  1. 1.Department of Earth SciencesIIT RoorkeeRoorkeeIndia
  2. 2.KolkataIndia

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