CSAMT勘探中场区、记录规则、阴影及场源复印效应的解析研究

由矢量位导出均匀大地表面上水平接地谐变电偶极子地下电磁场的闭合表达式, 将地层波和地面波显式地区分开来, 据此定义了与远区场和近区场对应的地面波区和地层波区. 对长期困扰CSAMT勘探工作者的记录点问题、阴影和场源复印效应问题给出了物理解释. 由地层波与地面波之比给出了定量划分场区的方法, 每一场分量最佳记录规则下的条件和判断是产生阴影和场源复印效应的前提. 山西沁水盆地CSAMT勘探覆盖点的推断结果表明, 阴影和场源复印效应是由地层波所携带的源与观测点之间、源下方真实地质情况的信息决定, 是可以利用的.

Analytical study on field zones, record rules, shadow and source overprint effects in CSAMT exploration

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.