Analytical study on field zones, record rules, shadow and source overprint effects in CSAMT exploration
CSAMT勘探中场区、记录规则、阴影及场源复印效应的解析研究

With vector potential of magnetic type this paper derives the closed form expressions of subsurface electromagnetic fields generated by a grounded horizontal harmonic electric dipole in a homogeneous half_space, which distinguish formation waves from surface waves explicitly. According this, we define surface_ and (subsurface_) wave zones corresponding to far_ and near_field zones. The record rules, shadow and source overprint effects, that have disturbed CSAMT explorers for a long time, are explained with physics. The methods of quantitatively dividing zones, the conditions of the optimum record rule for each component and the prerequisites for causing shadow and source overprint effects are provided by the ratio of formation wave to surface wave. The deduction of covering points of CSAMT prospecting in the Qinshui basin, Shanxi Province shows that the shadow and source overprint effects are real geological information carried by formation waves between the transmitting source and the observation point or beneath the source, which can be exploited.