Abstract:Theoretical studies of some controlled-source electromagnetic methods, especially the horizontal coaxial magnetic dipole-dipole and horizontal collinear electric dipole-dipole electromagnetic methods, which are capable of accurately measuring the relatively low conductivity of the seafloor were reviewed. Marine electromagnetic instrumentations, especially the time-domain horizontal magnetic dipole-dipole system and horizontal electric dipole-dipole system which have been designed and constructed in the Geophysics Division of the University of Toronto, were provided with applications to geotechnical studies on the shelf and deep ocean surveys near the mid-ocean ridges.

Key words: seafloor resources; electric conductivity maping; instruments