Quantifying the Media Bias in Intensity Surveys: Lessons from the 2001 Bhuj, India, Earthquake

Many seismologists have looked at the 26 January 2001 Bhuj earthquake as a key modern calibration event that could be used to improve estimates of magnitudes of large historic mainshocks in stable continental regions. Since no instrumental data are available for important historic events such as the 1819 Allah Bund, India, and the 1811–1812 New Madrid, central U.S. mainshocks, calibration hinges on comparisons of the macroseismic effects of these earthquakes with those of comparable modern earthquakes for which a reliable, instrumentally determined moment magnitude is available. However, although such a comparison is conceptually straightforward, in practice it is complicated by potentially significant inconsistencies in methods used to quantify macroseismic effects in different regions and/ or times. For the Bhuj earthquake, extensive intensity data sets have been compiled and published from both media accounts and detailed direct surveys. Comparing the two provides a quantification of the previously suspected media bias, whereby earthquake effects can be exaggerated in media accounts. This bias is a strong function of intensity level, with substantial bias at the highest shaking levels and significantly less bias at low intensities. Because only sparse documentary data are in general available for older historic earthquakes, the results of this study suggest that their inferred intensity distributions might be similarly biased. We further use the survey- based intensity values to develop a new relationship between intensities and ground motions.

[1]  R. Iyengar,et al.  Strong Ground Motion Estimation During the Kutch, India Earthquake , 2006 .

[2]  John Douglas,et al.  Magnitude calibration of north Indian earthquakes , 2004 .

[3]  S. Hough,et al.  Revisiting the 23 February 1892 Laguna Salada Earthquake , 2004 .

[4]  W. H. Bakun,et al.  Magnitudes and Locations of the 1811–1812 New Madrid, Missouri, and the 1886 Charleston, South Carolina, Earthquakes , 2004 .

[5]  D. Dreger,et al.  Rupture Process of the 26 January 2001 Mw 7.6 Bhuj, India, Earthquake from Teleseismic Broadband Data , 2003 .

[6]  Mario Ordaz,et al.  Estimation of ground motion for Bhuj (26 January 2001; Mw 7.6 and for future earthquakes in India , 2003 .

[7]  Martin J. Siegert,et al.  EOS Trans. AGU , 2003 .

[8]  Gail M. Atkinson,et al.  The 26 January 2001 M 7.6 Bhuj, India, Earthquake: Observed and Predicted Ground Motions , 2002 .

[9]  Pankaj Agarwal,et al.  Strong Motion Records , 2002 .

[10]  Linking Historical Intensity Observations with Ground-motion Relations for Eastern North America , 2001 .

[11]  E. Fielding,et al.  The 26 January 2001 “Republic Day” Earthquake, India , 2001 .

[12]  E. Fielding,et al.  The January 26, 2001 Bhuj, India Earthquake , 2001 .

[13]  Gail M. Atkinson,et al.  Empirical Relationships between Modified Mercalli Intensity and Response Spectra , 2000 .

[14]  Thomas H. Heaton,et al.  Relationships between Peak Ground Acceleration, Peak Ground Velocity, and Modified Mercalli Intensity in California , 1999 .

[15]  R. Musson,et al.  The Barrow-in-Furness Earthquake of 15 February 1865: Liquefaction from a Very Small Magnitude Event , 1998 .

[16]  G. Grünthal.  European Macroseismic Scale 1998 , 1998 .

[17]  Gail M. Atkinson,et al.  The Damage Potential of Eastern North American Earthquakes , 1993 .

[18]  C. W. Stover,et al.  Seismicity of the United States, 1568-1989 (revised) , 1993 .

[19]  Thomas C. Hanks,et al.  Common features of the excitation and propagation of strong ground motion for North American earthquakes , 1992 .

[20]  Walter H. F. Smith,et al.  Free software helps map and display data , 1991 .

[21]  N. Ambraseys,et al.  A history of Persian earthquakes , 1982 .

[22]  C. Strand.  Pre-1900 earthquakes of Baja California and San Diego County , 1980 .

[23]  Mihailo D. Trifunac,et al.  On the correlation of seismic intensity scales with the peaks of recorded strong ground motion , 1975 .

[24]  O. Nuttli,et al.  The Mississippi Valley earthquakes of 1811 and 1812: Intesities, ground motion and magnitudes , 1973, Bulletin of the Seismological Society of America.

[25]  R. Oldham,et al.  Report on the great earthquake of 12th June 1897 , 1899 .