The Fourth Workshop on Electromagnetic Induction in the Earth and Moon held in the Bavarian village of Murnau, West Germany, September 6–13,1978 had two notable features: one was improved methodology and the linking of electromagnetic information to other geophysical investigations, such as heat flow or seismology; the other was formal approval of a project for international cooperation in studies of electrical anomalies associated with the asthenosphere.
The workshop, sponsored by Working Group III of IAGA (International Association of Geomagnetism and Aeronomy), was devoted to probing electrical properties of the earth from the crust down to depths of 1000 km, as inferred from (a) magnetotellurics (MT), in which both electrical and magnetic observations are made; and (b) geomagnetic deep sounding (GDS), which uses purely magnetic variations. Although the depth resolution of these methods is usually poorer than seismic methods, lateral resolution is usually better. In addition, they have the advantage that a zone of anomalously high conductivity presents a strong effect, whereas seismic waves are absorbed or deflected downward by a low-velocity zone. It is this feature that makes MT and GDS attractive for studies of the asthenosphere. A summary of the meeting is presented below, followed by a discussion of the Soviet proposal to initiate an international program to study the electrical properties of the asthenosphere: Elas.