from K Kappler UCB and others

[skipped Intro]

Based on our analysis of these residuals we conclude that any anomalous magnetic signals would have to be at least 2-3 orders of magnitude weaker than those reported to preceed the Loma Prieta earthquake. A strong co-seismic signal was observed. Much of this signal can probably be explained by motion of the sensors in the Earth's main field, although local electrokinetic effects in the vicinity of the sensor may also have contributed to these signals. Statisitcal analysis has also been performed on variations of daily estimates of apparent resistivity and phase at Parkfield. Systematic variations in these parameters are observed, including slow seasonal modulations and more rapid changes on time scales of a few days. However, comparison to weather records suggest that these signals are most probably related to ground moisture and precipitation events, modifying near surface distortion of the electric fields. Multivariate statistical analysis, including principal components and canonical coherence analysis have also been applited to the data, allowing alternate views of temporal variations of signal and noise characteristics. Although there are some anomalous signals deserving more careful study, there is no evidence from this analysis for significant anomalous EM signals preceeding the Parkfield earthquake.