地中电偶极源极低频电磁场的分布与传播特征

Distribution and propagation characteristics of extremely low frequency electromagnetic field of electric dipole source in the Earth

利用层状大地中偶极源响应的正演算法,计算地中电偶极源激发的极低频地震电磁场并分析其在地球环境下的传播特征.设计了多个水平层状地球模型,分别模拟和展示了深埋地中的电偶极源的响应和空间分布特征.重点分析了含地壳波导+LAI波导模型的高阻大地中,倾斜电偶极源激励响应随观测点的偏移距和垂直位置、激励源深度、地壳波导结构和参数变化时各场量响应的幅频特征.研究表明,用倾斜电偶极源模拟和分析高阻大地中孕震电磁辐射的响应及在大地电磁系统中的传播特性是可行的;模拟的高阻大地中的电磁辐射在地壳波导和LAI波导中均表现有慢衰减或幅值增强特性,但两个波导效应具有不同的频率选择性;高阻大地中的电磁辐射在波导的高阻介质中具有幅值强、衰减慢的特点.建议在高阻地层出露的地表、井中或海底的高阻岩层中以及大气层中布设测站.

Based on the forward algorithm of dipole source response in layered earth, the propagation characteristics of an extremely low frequency of seismo-electromagnetic anomalies in the earth's environment are simulated and analyzed. Several typical horizontal layered earth models are designed to simulate and depict the response and spatial distribution characteristics of electric dipole sources underground. The amplitude-frequency characteristics of the excitation response of the inclined electric dipole source in the high resistivity earth with the crustal waveguide plus Lithosphere-Atmosphere-Ionosphere (LAI) waveguide model are analyzed, when the parameters change including the offset and vertical position of the observation point, the depth of the excitation source, and the structure and electromagnetic (EM) parameters of the crustal waveguide. The results show that it is feasible to simulate and analyze the response of seismo-electromagnetic radiation in the high resistivity earth and its propagation characteristics in the magnetotelluric system with the inclined dipole source. The EM radiation in high resistivity earth exhibits slow attenuation or even amplitude enhancement in both crustal waveguide and LAI waveguide, but the two waveguides have different frequency selectivity. It is suggested to set up stations on the surface where the high resistivity formation is exposed, in the well or on seabed with high resistivity rock layer, and the atmosphere.