Tectonomagnetic experiments and observations in wastern U.S.A.

Abstract

Simultaneous measurements of the geomagnetic field with differential proton magnetometers (0.25 gamma sensitivity) have been recorded periodically since 1973 at more than 100 pairs of sites, 8 to 12km apart, along active faults in western U. S. A. Along one 80km test section of the San Andreas fault the data from 7 instruments is continuously telemetered to Menlo Park, California. Probable tectonomagnetic effects with amplitudes of about 1 and 1.8 gammas have been observed for earthquakes with magnitudes 4.2 and 5.2 respectively. The corresponding stress changes for simple dislocation models are in the range 10 and 100 bars respectively. Magnetic and electrical response differences and site separation appear to be the most important factors determining discrimination limits for tectonomagnetic signals.