An NSF-sponsored workshop entitled “Low-Frequency Electrical Precursors to Earthquakes: Fact or Fiction?” was held at the Lake Arrowhead Hilton in California from June 14 to 17. Thirty-seven scientists participated in a review of past and current experiments that began with a poster session followed by an open discussion. Highlights of research presented at this workshop included seismic electric signals from Greece, precursory changes of resistivity in China, a reassessment of the ULF anomaly at Loma Prieta, and identification of geophysical constraints for mechanisms possibly causing precursory signals.
Discussion focused on instrumentation, laboratory studies, definition of anomalous signals, mechanisms, and the significance of correlations between anomalies and earthquakes. While much is still uncertain, some of the precursory phenomena exist and expanded measurement programs are warranted. The participants identified three main guidelines to improve and quantify their attempts to monitor electrical and electromagnetic precursors and to extend their understanding of the mechanisms responsible for the generation of precursory signals.