Studies of Source Mechanism for Seismic Electromagnetic Anomalies by Means of Charged Particle's Measurements

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The present study investigates the source mechanism of the seismic electromagnetic activities that occur in a geo-tribosystem. It was shown that granite generates thermally stimulated exoelectron emission (TSEE) at temperatures ranging from 300℃ to 400℃. This emission is released from the trapped levels at intrinsic and extrinsic centres in the minerals. Possible heat sources for TSEE are discussed in terms of the frictional heating of the precursor slip. Fracture-induced transient electric signals (FITESs), propagated through the rocks, could be detected only immediately prior to the final fracture. FITES was detected not only from quartz bearing rock (granite) but also from quartz-free rocks, (gabbro and serpentinite), except marble. The FITES intensity decayed in proportion to the distance from the fracture zone. Less FITES was detected for granite annealed at a temperature of 400℃, where the piezoelectric effect was unchanged but the exoelectron sites were reset. This confirms that the main source of FITES and seismic electric activity is probably the trapped electrons.
独立行政法人防災科学技術研究所の論文
1995-03-31