地磁场的变化在岩石中所感生的电流,可以用来测定电阻率。如果磁场的时间变化能够当作平面电磁波的磁分量来研究,则磁场变化的振幅、在大地感生的电位梯度和大地电阻率这三者之间存在着一个简单的关系。同时,由于电磁波在导体中的穿透深度取决于频率和导体的电阻率,所以若能测出几个频率的磁场和电场变化的振幅,则可以计算出在大地中不同深度的电阻率。磁大地电流法测定电阻率比直流电法有两个重要的优点。首先,由于测量是利用大地中感生的电流。所以在测定高阻层下的电阻率时,就不会遇到象直流电法测量时所存在的问 Changes in the geomagnetic field The current induced in the rock can be used to determine the resistivity. If the time variation of a magnetic field can be considered as the magnetic component of a planar electromagnetic wave, then there is a simple relationship between the magnitude of the magnetic field change and the magnitude of the earth-induced potential gradient and the earth resistivity. At the same time, since the depth of penetration of electromagnetic waves in a conductor depends on the frequency and the resistivity of the conductor, the resistivity at different depths in the earth can be calculated if the magnetic field at several frequencies and the amplitude of the electric field change can be measured. Magnetic earth current method to determine the resistivity than the DC method has two important advantages. First of all, because the measurement is the use of induced currents in the earth. So in the determination of the resistivity of the high resistance layer, it will not encounter as measured by the DC method