岩溶体的天然电场选频法异常成因研究

A study of the anomaly genesis for the frequency selection method in a natural electric field of a karst body

在实地探测的基础上,主要是从理论模型的角度研究天然电场选频法异常的形成原因。首先在已知的充水岩溶上开展实地探测工作,获取实测异常曲线;从麦克斯韦方程组和边界条件出发,求取均匀垂直谐变一次磁场中良导球体和圆柱体内、外磁场矢量位,推导出球外和圆柱体外感应二次电场的解析计算式;对理论模型的各个参数进行假定,计算获得地表主剖面上良导球体和圆柱体的感应二次电场异常曲线。通过实测曲线与理论模型上的模拟计算结果对比分析可知,二者曲线形态相似、特征相同,由此推知天然电场选频法在含水低阻体上方测得异常的起因之一可能是由天然感应二次电场所致。

On the basis of in situe detection,the main purpose of this paper is to study the anomaly genesis of the frequency selection method.In situ detection is performed in a water-filled cave,and practical anomaly curves are obtained.Based on the Maxwell equations and the boundary conditions,magnetic vector potential of a low resistivity sphere or a horizontal cylinder in a homogeneous harmonious vertical magnetic field is solved.The analytic expressions of an induced electric field outside the abnormities are obtained.Parameters of the model are assumed,and anomaly profiles of the induced electric field are also obtained.Results between practical prospecting curves are compared with theoretical simulating curves,and similar characteristics are indicated.The anomaly genesis of the frequency selection method is induced in the natural electric field for a water-filled low resistivity abnormity.The induced natural electric field is one of the important factors causing anomalies.