Some factors concerning electromagnetic wave propagation in the earth's crust

This paper is a brief survey of the geophysical considerations which govern propagation of electromagnetic waves in the earth's crust. It is indicated that the electrical conductivity of crustal materials depends, in a very complicated manner, on moisture content, porosity, temperature, and pressure. It is suggested that communication ranges in the crust will seldom exceed 100 km except when basement rock conductivities are less than 10
^-6
mho/meter.