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On the reported magnetic precursor of the 1993 Guam earthquake
Author(s) -
Thomas Jeremy N.,
Love Jeffrey J.,
Johnston Malcolm J. S.,
Yumoto Kiyohumi
Publication year - 2009
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2009gl039020
Subject(s) - epicenter , magnetometer , seismology , observatory , magnetic anomaly , geology , physics , polarization (electrochemistry) , geodesy , magnetic field , geophysics , astrophysics , chemistry , quantum mechanics
Using 1‐second magnetometer data recorded 67 km from the epicenter of the 1993 M w 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.