Pure and Applied Geophysics

, Volume 169, Issue 12, pp 2127–2138 | Cite as

An Appraisal of the 2001 Bhuj Earthquake (Mw 7.7, India) Source Zone: Fractal Dimension and b Value Mapping of the Aftershock Sequence

  • J. R. Kayal
  • Vishal Das
  • Uma Ghosh


We examined seismic characteristics, b value and fractal dimension of the aftershock sequence of the January 26, 2001 Bhuj earthquake (Mw 7.7) that occurred in the Kutch failed rift basin, western margin of the Stable Continental Region (SCR) of India. A total of about 2,000 events (M ≥ 2.0) were recorded within two and a half months, immediately after the main shock. Some 795 events were precisely relocated by simultaneous inversion. These relocated events are used for mapping the frequency-magnitude relation (b value) and fractal correlation dimension (Dc) to understand the seismic characteristics of the aftershocks and the source zone of the main shock. The surface maps of the b value and Dc reveal two distinct tectonic arms or zones of the V-shaped aftershock area, western zone and eastern zone. The b value is relatively higher (~1.6) in the western zone compared to a lower value (~1.4) in the eastern zone. The Dc map also shows a higher value (1.2–1.35) in the western zone compared to a lower Dc (0.80–1.15) in the eastern zone; this implies a positive correlation between Dc and b value. Two cross sections, E–W and N–S, are examined. The E–W sections show similar characteristics, higher b value and higher Dc in the western zone and lower in the eastern zone with depth. The N–S sections across the fault zones, however, show unique features; it imaged both the b and Dc characteristics convincingly to identify two known faults, the Kutch Mainland fault and the South Wagad fault (SWF), one stepping over the other with a seismogenic source zone at depth (20–35 km). The source zone at depth is imaged with a relatively lower b and higher Dc at the ‘fault end’ of the SWF showing a negative correlation. These observations, corroborated with the seismic tomography as well as with the proposed geological/tectonic model, shed a new light to our understanding on seismogenesis of the largest SCR earthquake in India in the recent years.


Main shock aftershocks b value fractal dimension seismogenic fault 



We sincerely thank the editor and the reviewers for their constructive suggestions and comments to improve the manuscript to its present form. In the event of successful completion of the work, one of the authors, VD would like to thank the head, Department of Applied Geophysics, Indian School of Mines, Dhanbad for allowing him to undertake the project as part of his summer research work at the School of Oceanographic Studies, Jadavpur University, Kolkata, India. Ms Sohini Roy, Jadavpur University is gratefully acknowledged for her help and cooperation in some of the computational work.


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© Springer Basel AG 2012

Authors and Affiliations

  1. 1.School of Oceanographic StudiesJadavpur UniversityKolkataIndia
  2. 2.Department of Applied GeophysicsIndian School of MinesDhanbadIndia
  3. 3.Lalbaba CollegeCalcutta UniversityHowrahIndia

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