Geological and geophysical considerations in radio propagation through the earth's crust

Geological and geophysical considerations applicable to radio propagation through the rock strata at the basement complex are presented. Information on electrical characteristics of rocks based on laboratory measurements on samples is shown to be misleading because in situ conditions are very difficult to analyze and reproduce. The complexity of the basement geology adds to the difficulty of predicting in situ rock characteristics pertinent to radio propagation. Folding and fracturing of the strata, variegated rock types and the anistropy of rock resistivity cause the actual propagation path loss to be vastly different than that predicted on the basis of a simple geological model. This conclusion is supported by the available experimental data. Deep resistivity measurements made from the surface indicate that basement strata will have resistivities of the order of
10^{3}-10^{4}
ohm-meters over most of the United States.