Foreword and Introduction

Abstract

Over the last few years there has been a dramatic surge of interest in time‐domain electromagnetic (TDEM) methods of exploration as evidenced by the proliferation of commercially available time‐domain equipment and contractors, by the extensive research carried out at various companies and universities, and by the large number of papers published on the subject. At the last few SEG Annual Meetings there were special sessions devoted solely to TDEM and there was even a time‐domain electromagnetic workshop at the SEG Annual Meeting in Las Vegas. As such, it is not difficult to understand the motivation for preparing this Special Issue of Geophysics devoted to TDEM techniques: to present recent advances and to give us a glimpse at the future. At this moment it seems appropriate to trace the evolution of transient techniques from their early beginnings to the present. Historically, TD techniques have evolved along two parallel paths, transient EM soundings and transient EM prospecting (or inductive TDEM). The first technique is used primarily to delineate layered structures of interest in oil and groundwater exploration. It is also used in delineating zones of high conductivity within the ground, with the expectation that they might be associated with either geothermal or massive sulfide targets. By contrast, transient EM prospecting is primarily used for locating massive sulfide ore deposits at great depths, and its use is associated almost exclusively with the mining industry.