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The 26 January 2001 M 7.6 Bhuj, India, Earthquake: Observed and Predicted Ground Motions

Hough, Susan E. and Martin, Stacey and Bilham, Roger and Atkinson, Gail M. (2002) The 26 January 2001 M 7.6 Bhuj, India, Earthquake: Observed and Predicted Ground Motions. Bulletin of the Seismological Society of America, 92 (6). pp. 2061-2079. ISSN 0037-1106. doi:10.1785/0120010260.

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Although local and regional instrumental recordings of the devastating 26, January 2001, Bhuj earthquake are sparse, the distribution of macroseismic effects can provide important constraints on the mainshock ground motions. We compiled available news accounts describing damage and other effects and interpreted them to obtain modified Mercalli intensities (MMIs) at >200 locations throughout the Indian subcontinent. These values are then used to map the intensity distribution throughout the subcontinent using a simple mathematical interpolation method. Although preliminary, the maps reveal several interesting features. Within the Kachchh region, the most heavily damaged villages are concentrated toward the western edge of the inferred fault, consistent with western directivity. Significant sediment-induced amplification is also suggested at a number of locations around the Gulf of Kachchh to the south of the epicenter. Away from the Kachchh region, intensities were clearly amplified significantly in areas that are along rivers, within deltas, or on coastal alluvium, such as mudflats and salt pans. In addition, we use fault-rupture parameters inferred from teleseismic data to predict shaking intensity at distances of 0–1000 km. We then convert the predicted hard-rock ground-motion parameters to MMI by using a relationship (derived from Internet-based intensity surveys) that assigns MMI based on the average effects in a region. The predicted MMIs are typically lower by 1–3 units than those estimated from news accounts, although they do predict near-field ground motions of approximately 80%g and potentially damaging ground motions on hard-rock sites to distances of approximately 300 km. For the most part, this discrepancy is consistent with the expected effect of sediment response, but it could also reflect other factors, such as unusually high building vulnerability in the Bhuj region and a tendency for media accounts to focus on the most dramatic damage, rather than the average effects. The discrepancy may also be partly attributable to the inadequacy of the empirical relationship between MMI and peak ground acceleration (PGA), when applied to India. The MMI–PGA relationship was developed using data from California earthquakes, which might have a systematically different stress drop and therefore, a different frequency content than intraplate events. When a relationship between response spectra and MMI is used, we obtain larger predicted MMI values, in better agreement with the observations.

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Hough, Susan E.0000-0002-5980-2986
Additional Information:© 2002 Seismological Society of America. Manuscript received 12 October 2001. We thank S. K. Singh, Kali Wallace, Martitia Tuttle, Tousson Toppozada, and Bill Bakun for helpful discussions and suggestions that greatly improved the manuscript; we also thank Igor Beresnev for helpful comments and for making available his ground-motion-modeling code. Maps were generated using GMT software [Wessel and Smith, 1991]. Research by S. Martin was supported by the Southern California Earthquake Center. SCEC is funded by NSF Cooperative Agreement EAR-8920136 and USGS Cooperative Agreements 14-08-0001-A0899 and 1434-HQ-97AG01718. The SCEC contribution number for this article is 608.
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USGS Cooperative Agreement1434-HQ-97AG01718
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Issue or Number:6
Record Number:CaltechAUTHORS:20140801-105512897
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Official Citation:Hough, S. E., Martin, S., Bilham, R., & Atkinson, G. M. (2002). The 26 January 2001 M 7.6 Bhuj, India, Earthquake: Observed and Predicted Ground Motions. Bulletin of the Seismological Society of America, 92(6), 2061-2079. doi: 10.1785/0120010260
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:47790
Deposited On:04 Aug 2014 18:23
Last Modified:10 Nov 2021 17:50

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