Deep resistivity measurements in the Pacific Northwest

Abstract

Deep resistivity measurements in eastern Oregon and Washington show that significant lateral changes occur within the upper 40 km of the earth's crust. The most dramatic transition occurs within 50 km of the Oregon-Washington border and suggests a major structure there. Measurement separations extended to 190 km. The existence of a suspected electrically conductive zone at a depth of 70 km is consistent with the results of the experiment, although the conductive upper layer renders positive identification of such a region impossible. The upper 10 to 15 km of 100-ohm-m material is tentatively identified with surface exposures of the Columbia River basalts.