1 Introduction

In September 2009, I accompanied several members of a local geology team together with a Vendor’s field geophysicist to conduct an on-site EM survey using Vendor’s new electromagnetic sounding technique.

As alluded in the following sections, my report expressed certain reservations about the validity of his method. While trying to minimize such discussion, I have nonetheless repeated some of those considerations in order to provide context, and to retain some feel for some geophysical questions of the problem, whose consideration did pique my curiosity, and lead me to investigate the general distribution of electromagnetic free-mode eigenfrequencies in layered resistive media. Although the question is of no particular significance to geology here on earth, where subsurface resistivity is usually far too low for there to be any measurable effect [4, Section 2.2], I thought it an interesting theoretical question, and is the topic of this article.