The record of a vector proton magnetometer after the March 1964 Alaskan earthquake

Power spectrums of the data from a digitally recording, vector proton-precession magnetometer, which was operating at the time of the March 1964 Alaskan earthquake, give no evidence of magnetic fluctuations with frequencies of torsional modes in the earth's free oscillation spectrum. The absence of spectral peaks and the low spectral levels make it evident that if magnetic oscillations were present their amplitudes could not have exceeded 0.02 γ in total field or 0.05 γ in horizontal field. This is in conflict with an earlier analysis of conventional magnetic data after the 1960 Chilean earthquake. It seems possible that the earlier observations were purely fortuitous, but the analysis of digital magnetometer data after the next large earthquake is necessary to confirm our conclusion. The proton magnetometer data are more precise and more suitable for digital processing than variometer records, as reflected by the fact that our general spectral levels are ten times smaller than those of the earlier work. A survey of mechanisms by which such oscillations could have been induced shows them to be quite inadequate.