Transmission of subhertz electromagnetic waves from an inhomogeneous earth’s crust to the atmosphere

Abstract

For the study of electromagnetic fields generated by precursory effects of earthquakes, the problem of transmission to the atmosphere is investigated for a subhertz plane electromagnetic wave obliquely incident from a homogeneous earth’s crust of semi-infinite extent through an inhomogeneous earth’s crust of finite thickness. To analyze the problem, the inhomogeneous earth’s crust is subdivided into a number of thin homogeneous layers. Then, an easier problem of propagation through a composite multilayered medium replacing the homogeneous and inhomogeneous earth’s crusts and the atmosphere is treated. To confirm the validity of the above formulation, an exponential inhomogeneity for the conductivity of the earth’s crust is considered for a specific example. First, for the case of the inhomogeneous earth’s crust, the overall power transmission coefficient on the earth-atmosphere interface at normal incidence is found to show a broader frequency characteristic and to take a maximum value at a definite subhertz frequency, shifting to a lower frequency. For the general case of oblique incidence as well, these features of the overall power transmission coefficient are retained except in the vicinity of the critical angle of incidence for the H-wave. At the critical angle of incidence, the power flow density carried by a surface wave along the earth-atmosphere interface becomes anomalously large for the H-wave.