THE STRESS EFFECT ON REMANENT MAGNETIZATION OF ROCKS

In order to simulate the effect of tectonic stress on the remanent magnetization of rocks,an experiment with 44 samples of 6 types is carried out. The result shows that the nature of the changes of the remanence with the stress is far more complicated than estimated hitherto. The authors suggest that these phenomena could be divided into three types. In the weakly irreversible (typeⅠ) effect the remanence decreases with stress regularly and then is restored to nearly its original value when the stress is completely released. In the strongly irreversible (typeⅡ) effect the remanence is hardly restored when the stress is released. In the irregular (type Ⅲ) effect the remanence shows a very jumble variation with stress. An important reason that these rock samples show such different effects is,according to the results of comprehensive magnetic study on these rocks,the different contents of VRM contained in NRM of the samples,microscopically depending on the magnetic minerals in rocks and their domain states etc. The results imply that to interpret the piezomagnetic effects of earthquakes the sole simple piezomagnetic model of rocks is not enough,while the specific contents of rocks in the seismic regions involved need be considered.