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Jan/26/2001 (Mw 7.6), Bhuj, India

Alex Copley (Caltech)

Location of Epicenter






DATA Process and Inversion

The slip model here is based on the results pubilshed in Copley et. al. (2011) . We used the GSN broadband data downloaded from the IRIS DMC. We analyzed 21 teleseismic P waveforms and 19 SH waveforms selected based upon data quality and azimuthal distribution. Waveforms are first converted to displacement by removing the instrument response. We also used surface offset data derived from SPOT and InSAR satellite imagery and re-occupation of levelling lines, along with seismic data to constrain the slip history based on a finite fault inverse algorithm (Ji et al, 2002). The dip angle of the main fault plane is 51° and strike is 82°. 1D velocity model is extracted from the CRUST2.0 global tomography model (Bassin et al., 2000).


Result

The model shows a remarkably compact source, with slip of up to 14 m occurring in a ruptured patch which is ~30 km wide. The mean rupture velocity within the region of high slip is estimated to be 2.2~2.4 km/s.


Cross-section of slip distribution



Figure 1: The upper panel shows our calculated slip distribution for the Bhuj earthquake. The red star shows the hypocentre, and the black line shows where the two planes intersect at the surface. The lower panel shows in map view the surface intersections of the two fault planes (white lines), and the locations of aftershocks. Also shown is a comparison of focal mechanisms for the earthquake. A & D: Antolik and Dreger (2003).


Comparison of data and synthetic seismograms




Figure 2: Observed (black) and modelled (red) teleseismic waveforms. The maximum amplitude of each seismogram is shown on the right of the trace. The source time function of our model is shown in the top right.


Static observation and synthetic fits



Figure 3: Fits between the modelled and observed surface deformation. The large panel shows the modelled line-of-sight displacement for a descending- track SAR interferogram, with the contours labelled in metres. The thick black lines show the surface intersections of the main and secondary model fault planes. The white bars with error bounds show vertical displacements, and the red arrows show the model predictions at the same locations. The smaller panels show the InSAR results of Schmidt and Burgmann (2006), labelled with the dates of the SAR images used, along with the residuals between the data and the model (shown as the data value minus the model prediction). The four panels on the right all cover the same geographical area, shown by the easternmost red box on the main panel. The small black arrows show the satellite look direction.

Comments:



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(Slip Distribution)

SUBFAULT FORMAT


References

Copley,A., J.P. Avouac, J. Hollingsworth & S. Leprince, The 2001 Mw 7.6 Bhuj earthquake, low fault friction, and the crustal support of plate driving forces in India , JOURNAL OF GEOPHYSICAL RESEARCH , VOL. 116, B08405, 11 PP., 2011

Ji, C., D.J. Wald, and D.V. Helmberger, Source description of the 1999 Hector Mine, California earthquake; Part I: Wavelet domain inversion theory and resolution analysis, Bull. Seism. Soc. Am., Vol 92, No. 4. pp. 1192-1207, 2002.

Antolik, M. and D. S. Dreger, Rupture Process of the 26 January 2001 Mw 7.6 Bhuj, India, Earthquake from Teleseismic Broadband Data, Bull. Seism. Soc. Am., Vol. 93, No. 3, pp. 1235ĘC1248, 2003

GCMT project: http://www.globalcmt.org/

USGS National Earthquake Information Center: http://neic.usgs.gov



Global Seismographic Network (GSN) is a cooperative scientific facility operated jointly by the Incorporated Research Institutions for Seismology (IRIS), the United States Geological Survey (USGS), and the National Science Foundation (NSF).

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