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On the reported magnetic precursor of the 1993 guam earthquake

January 1, 2009

Using 1-second magnetometer data recorded 67 km from the epicenter of the 1993 Mw 7.7 Guam earthquake, Hayakawa et al. (1996) and Miyahara et al. (1999) identify anomalous precursory changes in ultra-low frequency magnetic polarization (the ratio of vertical to horizontal field components). In a check of their results, we compare their data (GAM) with 1-second data from the Kakioka observatory (KAK) in Japan and the global magnetic activity index Kp. We also examine log books kept by USGS staff working on the Guam magnetic observatory. We find (1) analysis problems with both Hayakawa et al. and Miyahara et al., (2) significant correlation between the GAM, KAK, and Kp data, and (3) an absence of identifiable localized anomalous signals occurring prior to the earthquake. The changes we do find in polarization are part of normal global magnetic activity; they are unrelated to the earthquake. Copyright 2009 by the American Geophysical Union.

Publication Year 2009
Title On the reported magnetic precursor of the 1993 guam earthquake
DOI 10.1029/2009GL039020
Authors J.N. Thomas, J.J. Love, M.J.S. Johnston, K. Yumoto
Publication Type Article
Publication Subtype Journal Article
Series Title Geophysical Research Letters
Index ID 70036023
Record Source USGS Publications Warehouse