ANNUAL VARIATIONS IN DIRECTION OF EARTH RESISTIVITY AND THE TECTONIC STRESS FIELD IN CONTINENTAL CHINA

This work starts with some measurements of resistivity of rock specimen from mines and of certain concrete underground supports under stress for observing their variations of resistivity with direction. The results show that parallel to the stress, the amplitudes of the annual variations become minimum while maximum perpendicular to it. Halfway between, at an angle of about 45 to the stress direction, the amplitude values of annual variation of resistivity are medium.Based on such a preliminary observation, we used the data of 98 earth resistivity stations scattered all over continental China and divide the entire territory into three stress regions, namely, (1) the West China stress region, with nearly northsouth stress direction; (2) the North China stress region with northeast stress direction; (3) Southeast China stress region with eastwest stress direction. It is thus possible to show the directions of stress field in different parts of the country and at different times by observing in three directions at equal electrode spacings the annual variations of earth resistivity.