Exploration in the basalt‐covered areas of the Columbia River Basin, Washington, using electromagnetic array profiling (EMAP)

Abstract

The electromagnetic array profiling (EMAP) exploration method was tested at three basalt‐covered locations on the Columbia Plateau in central Washington state. Three 16 km survey lines were located to intersect test wells drilled by Shell. The data were EMAP filtered, and inverted using a nonlinear 1-D Riccati approach developed for conventional magnetotelluric (MT) processing. Large and small features on the resulting resistivity cross‐sections produced by EMAP filtering near the drill hole closely approximated the electric induction logs. Sedimentary units within the survey area appear to be thin, with some thickening indicated toward the center of the basin. Structuring within the sediments is mild within the limits of the survey, although there is appreciable structure within the Miocene flood basalts on one test line.