摘要
Introduction The degree of earth-resistivity anisotropy was described (MAO, et al, 1995, 1998) as follows: S=|1\nn∑I=1(ρSN\ρEW)I|-1|×103 n=6(1) whereρNS and ρEW are monthly mean values of earth resistivity in the direction of NS and EW, respectively, S is the half-year value. Equation (1) shows that if ρNS=ρEW, then S =0 and the electrical property of medium is isotropic; if ρNS≠ρEW, then S≠0 and the electrical property of medium is anisotropic. When S increases, the anisotropy of electrical property of medium is enhanced. Because the rightside of equation (1) is absolute value and the possibility ofρNS＞ρEW and ρNS＜ρEW can be different at different stations, the increase or decrease of S cannot reflect the relative changes between ρNS and ρEW. FENG, et al (2000) defined S as follows:……
