f Electromagnetic mapping of electrical conductivity beneath the Columbia basalt

The Colombia basalts cover a petroliferous sedimentary section and they present a representative example of the challenging problems of trying to determine sedimentary thickness and structure in situations where seismic methods do not provide adequate depth of exploration . Between 1979 and 1986 Shell conducted a series of controlled source (CSEM) and natural field (MT) surveys at several sites in the Columbia basalts and the results for a profile near Boylston are described in this study .