Reproducibility of Remanent Magnetization Changes and Volumetric Strain with Multiple Stress Cycles

Abstract

A series of experiments have been conducted to determine the relationships between stress, volumetric strain and remanent magnetization of rocks. These parameters have been measured simultaneously at confining pressures up to 1.5 kbar and differential stress up to failure of the samples. The purpose of the experiments was to determine whether or not stress induced porosity changes in rocks could be correlated with variations in remanent magnetization. It is important to determine how inelastic strain behavior, such as dilatancy and creep, affects remanent magnetization in rocks because such behavior may occur in the earth before seismic or aseismic movements on faults. It is also of interest to relate mechanisms causing non-linear strain behavior (crack opening, growth or interaction) in rocks to the changes observed in remanent magnetization. If these phenomena are related, then magnetic changes may provide a means for monitoring rock deformation in tectonic regions. Furthermore, since most rocks in the focal regions of earthquakes have experienced many stress cycles, it is important to investigate the effect of multiple cycles to high stress levels (∼85 to 90% failure stress) on remanent magnetization of rocks.