E-E_φ广域视电阻率定义的改进方法及场特性识别

柳建新^{1, 2, 3}，佟铁钢^{1, 2, 3}，刘春明^{1, 2, 3}，周文斌^{1, 2, 3}，蒋奇云^{1, 2, 3}

(1. 中南大学 有色资源与地质灾害探测湖南省重点实验室，长沙 410083；
2. 中南大学 地球科学与信息物理学院，长沙 410083；3. 中南大学 地质调查研究院，长沙 410083)

摘 要：广域电磁法采用均匀大地表面水平电偶源的全区精确表达式定义广域视电阻率，与卡尼亚视电阻率相比，能更好地反映地电模型的电性特征。利用广域视电阻率定义方法定义了E-E_φ方式的广域视电阻率、远区视电阻率及近区视电阻率，考虑观测方位角的影响，同时得出了E-E_φ观测装置的装置系数和电磁响应函数。对3层介质的A型、Q型、K型和H型的一维正演计算分析表明：E-E_φ观测装置的广域电磁法的观测方位角的影响相当于φ=90°时观测坐标系的旋转，通过适当的校正，任意φ角的测深曲线更能真实地反映地电断面随深度的客观变化，综合3种不同视电阻率的分析，能够较好地识别人工源频率域测深中电磁场不同的渐近特性。基于E-E_φ方式的广域电磁法扩大了观测范围，具有更好的应用前景。

关键词：广域电磁法；E-E_φ装置；电磁响应函数；视电阻率；人工源频率测深

Recognition of electromagnetic field asymptotic properties and improved definition of wide field apparent resistivity on E-E_φ array

LIU Jian-xin^{1, 2, 3}, TONG Tie-gang^{1, 2, 3}, LIU Chun-ming^{1, 2, 3}, ZHOU Wen-bin^{1, 2, 3}, JIANG Qi-yun^{1, 2, 3}

(1. Key Laboratory of Non-Ferrous Resources and Geological Hazard Detection,
Central South University, Changsha 410083, China;
2. School of Geosciences and Info-Physics, Central South University, Changsha 410083, China;
3. Research Institute of Geological Survey, Central South University, Changsha 410083, China)

Abstract:Wide field electromagnetic method defines the apparent resistivity by the accurate expression of full-zone of horizontal electric dipole source in homogeneous earth surface. Compared with the Cagniard apparent resisitivity, it can preferably show the electrical characteristics of geoelectric model. The computational formula of the improved apparent resistivity of E-E_φ array in the wide field electromagnetic method, near-zone apparent resistivity and far-zone apparent resisitivity is defined, the influence of observed azimuth is considered and the coefficient of the observation array and electromagnetic response function is obtained by the pattern of wide field electromagnetic apparent resistivity definition. Based on the calculation and analysis of curve A, curve Q, curve K and curve H of three-layer model in 1-D forward modeling, the influence of observation azimuth (φ) is equal to the rotation of the coordinate system at φ=90° in the wide field electromagnetic sounding of the E-E_φ array. Through proper calibration, the sounding curve of the arbitrary angle azimuth (φ) can more truly show the objective change of geoelectric section with the depth. Through comprehensive analysis of three different apparent resistivities, the different asymptotic characteristics of electromagnetic field in the controlled source frequency sounding method can be well identified. The wide field electromagnetic sounding method based on the observation of E-E_φ array can expand the observed scope, and has better prospect of application.

Key words:wide field electromagnetic method; E-E_φ array; electromagnetic response function; apparent resistivity; controlled source frequency sounding