Further evidence of localized geomagnetic field changes before the 1974 Thanksgiving Day Earthquake, Hollister, California

Seven weeks prior to the M=5.1 Hollister, Calif., Thanksgiving Day earthquake of 28 November, 1974, an anomalous magnetic variation was observed at one of the magnetometers of the USGS array. The anomaly lasted for about three weeks. Recently developed methods of reducing noise on magnetic records reveal that anomalous magnetic changes occurred at about the same time at three, of the six stations analysed. Such changes have not been seen either previously or subsequently. The largest variation occurred at the two stations closest to the earthquake, but a change also occurred at a station 44 km to the south.