THE EXPERIMENTAL RESULTS OF VARIATIONS IN THE SUSCEPTIBILITY OF ROCK SAMPLES UNDER UNIAXIAL STRESS BY TWO DIFFERENT APPROACHES

This paper shows the results of piezomagnetic experiments on eight kinds of strong magnetic rocks collected in the Beijing-Tangshan area of China under uniaxial pressure. The features of variation in magnetic susceptibility with increasing stress until fracture and even after fracture have been observed. It is shown that the variation in magnetic susceptibility is mainly a function of stress but not of strain,volume change,or relaxation. The large volume change marked by strong acoustic emission under a stable stress didn't cause any obvious,excessive change in susceptibility. Thus,this puts a negative factor on the possible dilatancy-magnetic precursor of earthquakes.Comparing the experimental results from two different approaches,this paper shows that the results are quite consistent. Thus it is shown that a simple detector attached to.the surface of the sample will provide a powerful tool in studying the variation in susceptibility. This makes the synchronous measurements of susceptibility,bulk strain,accoustic emission etc. easier.This paper also discusses the two types of piezomagnetic curves and their possible physical meaning.The measured coefficients of piezomagnetic variation versus stress range around -(0.4-3.0)10-3 MPa-1 for the rocks tested.