HR: 08:15h
AN: S41D-02    [Abstracts]
TI: The 1989 Ms 7.1 Loma Prieta, California, Magnetic Earthquake Precursor Revisited
AU: * Thomas, J N
EM: jnthomas@usgs.gov
AF: Geomagnetism Program, USGS, PO Box 25046, MS-966, Denver, CO 80225, United States
AU: * Thomas, J N
EM: jnthomas@usgs.gov
AF: Dept. Of Earth and Space Sciences, University of Washington, Box 351310, Seattle, WA 98195, United States
AU: Love, J J
EM: jlove@usgs.gov
AF: Geomagnetism Program, USGS, PO Box 25046, MS-966, Denver, CO 80225, United States
AU: Johnston, M J
EM: mal@usgs.gov
AF: Earthquake Hazards Program, USGS, 345 Middlefield Road, Menlo Park, CA 94025, United States
AB: Repeatable prediction of individual large earthquakes on the basis of quantitative geophysical data has proven to be frustratingly difficult and fraught with controversy. Still, some claims of success have been published, and among these are reports of identifiable precursory changes in magnetic-field activity as measured by ground- based magnetometers. By far the most prominent of such claims is that of Fraser-Smith et al., GRL, 17, 1465- 1468, 1990 who identified changes in Ultra Low Frequency (ULF, 0.01-10 Hz) magnetic noise prior to the 18 October 1989 Ms 7.1 Loma Prieta, California earthquake. The Fraser-Smith et al. result has been frequently cited in the literature, and it has been a major motivational influence for new research programs involving large arrays of ground-based instruments and even some satellite-based systems. We re-examine the data of the reported precursor, comparing them against independent data collected by magnetometers located in Japan and in the United States at the time of the Loma Prieta earthquake. From our analysis we infer that the key components of the precursory signal identified by Fraser-Smith et al. can be explained by minor corruption of the data in the form of a gain enhancement and time-stamp missassignment, possibly due to digital processing errors or inadvertent post-acquisitional treatment. We conclude that the reported magnetic anomaly is not related to the Loma Prieta earthquake.
UR: http://geomag.usgs.gov/
DE: 1500 GEOMAGNETISM AND PALEOMAGNETISM
DE: 1513 Geomagnetic excursions
DE: 5109 Magnetic and electrical properties (0925)
DE: 7200 SEISMOLOGY
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
SC: Seismology [S]
MN: 2007 Fall Meeting