1978 Volume 30 Issue 5 Pages 585-592
The erects of hydrostatic pressure up to 2.7kb on the susceptibility of magnetite single crystals, rocks and ore, and synthetic samples were studied. Susceptibility was measured using both static and alternating-frequency methods, with cyclic change of hydrostatic pressure and with time-dependent experiments. For a single crystal, susceptibility at saturation remanence decreases with pressurization, by about 25% for 2.5kb, and is recovered reversibly upon release of pressure. For rocks and ore, susceptibility k0 at small natural remanence increases slightly up to 0.2-0.8kb, then decreases at higher pressures at rates up to -10%/kb. It recovers upon pressure release. For cyclic pressurization without a time lag between cycles, the initial increase is not observed. Annealing increases the value of k0, and also suppresses the initial increase of k0 with pressure. Time lags of hours between pressure cycles result in recovery of pre-pressurization values of susceptibility. This work is intended to assist in the interpretation of stress-induced changes observed for rocks in the earth's lithosphere. Applications are in understanding piezomagnetic field changes as precursors for earthquake prediction, and study of other secular tectonomagnetic changes.
