The Remanence Variation of Rocks Stressed to Failure and Its Implication to Earthquake Prediction.

In the present study, an experiment under uniaxial pressure with 126 samples of 26 rock types is carried out. The general nature of remanence changes with stress is far more complicated than estimated hitherto. The authors suggest that these changes can be distinguished into three types. In Type-I and -II effects, the changes of remanence with stress are. all regular, however the former is weakly irreversible and the latter is strongly irreversible when the stress is released. In Type-III effect, the remanence shows a very jumbly and irregular variation with stress. According to the comprehensive study on magnetism of these rocks, the appearance of the Type-III effect is relevant to dominant VRM in NRM and specific domain state of the magnetic minerals in the rocks. In this experiment it is also discovered that a sort of relatively high-frequency variation superimposes on the general change of remanence under pressure. It appears to be related with the closing of existed microcracks and opening of newly-developing microcracks. Above-mentioned three types of piezomagnetic effect seem corresponding to certain kinds of earthquake precursors, while some sorts of tremble-variation in magnetization could be distinguished from local magnetic field data. The results of this experiment imply that in order to search and understand complicated seismomagnetic effects, specific content and microscopic structure of medium in seismic regions should be noticed.