Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Full Text (PDF) References Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Zúñiga, F. R. Articles by Wyss, M. Search for Related Content GeoRef GeoRef Citation

Inadvertent changes in magnitude reported in earthquake catalogs: Their evaluation through b-value estimates

Instituto de Geofisica Universidad Nacional Autónoma de México, Coyoacan, C.P. 04510, México City, México
Geophysical Institute University of Alaska, Fairbanks, Alaska

Abstract

A simple procedure is presented for analyzing magnitudes and seismicity rates reported in earthquake catalogs in order to discriminate between inadvertently introduced changes in magnitude and real seismicity changes. We assume that the rate and the frequency-magnitude relation of the independent background seismicity do not change with time. Observed differences in the frequency-magnitude relation (a and b values) between data from two periods are modeled as due to a transformation of the magnitude scale. The transformation equation is found by a least-squares-fitting process based on the seismicity data for earthquakes large enough to be reported completely and by comparing the linear relation of one period to the other. For smaller events, an additional factor accounting for increased (decreased) detection is allowed. This fitting technique is tested on a data set from Parkfield for which two types of magnitudes, amplitude and duration, were computed for each earthquake. We found that the b-value fitting technique yielded virtually the same result as a linear regression assuming the same errors in the two magnitudes. The technique is also applied to interpret the nature of reporting rate changes in a local (Guerrero, Mexico) and a regional (Italy) earthquake catalog. In Guerrero, a magnitude change in 1991.37 can be modeled about equally well by M_new = M_old + 0.5 or by M_new = 1.02 M_old + 0.38, but residuals with the latter transformation are smaller. In Italy, a magnitude change in 1980.21 cannot be modeled satisfactorily by a simple magnitude shift but is well described by a compression of the magnitude scale given by M_new = 0.67 M_old + 1.03.

The proposed b-slope fitting method provides a means to interpret quantitatively, and in some cases correct for, artificial reporting rate changes in earthquake catalogs.

This article has been cited by other articles:

				K.-P. Chen and Y.-B. Tsai A Catalog of Taiwan Earthquakes (1900-2006) with Homogenized Mw Magnitudes Bulletin of the Seismological Society of America, February 1, 2008; 98(1): 483 - 489. [Abstract] [Full Text] [PDF]

				S. Husen, S. Wiemer, and R. B. Smith Remotely Triggered Seismicity in the Yellowstone National Park Region by the 2002 Mw 7.9 Denali Fault Earthquake, Alaska Bulletin of the Seismological Society of America, December 1, 2004; 94(6B): S317 - S331. [Abstract] [Full Text] [PDF]

				M. Wyss, C. G. Sammis, R. M. Nadeau, and S. Wiemer Fractal Dimension and b-Value on Creeping and Locked Patches of the San Andreas Fault near Parkfield, California Bulletin of the Seismological Society of America, April 1, 2004; 94(2): 410 - 421. [Abstract] [Full Text] [PDF]

				J. J. Sanchez, S. R. McNutt, J. A. Power, and M. Wyss Spatial Variations in the Frequency-Magnitude Distribution of Earthquakes at Mount Pinatubo Volcano Bulletin of the Seismological Society of America, April 1, 2004; 94(2): 430 - 438. [Abstract] [Full Text] [PDF]

				Most- and Least-Likely Locations of Large to Great Earthquakes along the Pacific Coast of Mexico Estimated from Local Recurrence Times Based on b-Values Bulletin of the Seismological Society of America, December 1, 2001; 91(6): 1717 - 1728.

				M. Wyss and S. Wiemer Change in the Probability for Earthquakes in Southern California Due to the Landers Magnitude 7.3 Earthquake Science, November 17, 2000; 290(5495): 1334 - 1338. [Abstract] [Full Text]

				Is Background Seismicity Produced at a Stationary Poissonian Rate? Bulletin of the Seismological Society of America, October 1, 2000; 90(5): 1174 - 1187.

				Minimum Magnitude of Completeness in Earthquake Catalogs: Examples from Alaska, the Western United States, and Japan Bulletin of the Seismological Society of America, August 1, 2000; 90(4): 859 - 869.

				Mapping and Removing Quarry Blast Events from Seismicity Catalogs Bulletin of the Seismological Society of America, April 1, 2000; 90(2): 525 - 530.

				M. Wyss, R. Console, and M. Murru Seismicity rate change before the Irpinia (M = 6.9) 1980 earthquake Bulletin of the Seismological Society of America, April 1, 1997; 87(2): 318 - 326. [Abstract] [PDF]