Continental and oceanic structure from the Oregon coast westward across the Juan de Fuca Ridge

Abstract

Seismic and gravity data were used to construct crustal and subcrustal sections from the Tufts Abyssal Plain, west of the coast of Oregon, to southern Idaho. Nearly the entire area appears to be in isostatic equilibrium. Mantle depths west of the Juan de Fuca Ridge, in eastern Oregon, and in southern Idaho are normal for the surface elevations or water depths at these locations, and the corresponding mantle densities and velocities appear to be 'normal'. The mantle under the Juan de Fuca Ridge and the Cascadia Basin (west of Oregon) is relatively shallow and its density appears to be below normal to a considerable depth. Two different mantle structures are considered that are consistent with the seismic and gravity data. Magnetic data were not found to be diagnostic in differentiation between these two structures.Across the continental margin the Mohorovicic discontinuity dips sharply under the continents, being at a typical depth of 18 km near the coast line. The discontinuity is relatively shallow under western Oregon (as has been proposed previously), and the corresponding mantle is described in terms of apparent velocity and density.

Continuous seismic profiling investigation of the southern Oregon continental shelf between Cape Blanco and Coos Bay

“…Surface-ship, gimbal-mounted gravimeter surveys have been conducted off the Oregon coast to abyssal depths by the Oregon State University Geophysics Research Group. The free-air gravity anomaly maps west of Oregon have been published by Dehlinger, Couch, andGemperle (1967 and. Along the southern Oregon coast, two pronounced large negative anomalies are noted on the continental shelf (Figure 3).…”

Marine geophysics

“…The deeper structure has been examined by means of seismic refraction measurements in a number of areas previously unstudied [Ludwig et al, 1968a, 19686;Shor etal, 1968a, 19686;Bunce et al, 19 69;Murauchi et al, 1968;Francis and Raitt, 1967;Von Heune and Shor, 1969;Shor et al, 1968;Gardner, 1970;Den et al, 1969]. Anistropy in the mantle was observed and studied in several areas [ Morris etal, 1969;Raitt, 1969].…”

“…Anistropy in the mantle was observed and studied in several areas [ Morris etal, 1969;Raitt, 1969]. Emphasis was given to studies of the deep structure of continental margins, regions selected as warranting special attention by the Upper Mantle Committee [ Drake and Kosminskaya, 1969;Drake, 1969;Drake et al, 1968;Antoine etal, 1967;Heezen, 1968;Ludwig et al, 1968a, 19686;Sheridan and Drake, 1968;Sheridan et al, 1969, Worzel, 1968aMayhew et al,1970;Shor et al, 19696;Dehlinger et al, 1968;Morgan, 1968;Merkel and Alexander, 1969;Ley den et al, 1971;Taylor et al, 1968]. The crustal structure of a number of continental margins has now been examined, but it is clear that more work and new techniques will be required to determine the nature of the deep transition from continent to ocean.…”

Proceedings of workshop XLIV; geological, geophysical, and tectonic setting of the Cascade Range

“…In this study I attempt to delineate the structure of the overriding North American plate in southwest Washington in order to separate its effect from that of the subducting Juan de Fuca plate in the observed gravity anomalies. Part of this study is an update of Dehlinger and Couch's (1968) and Riddihough's (1979) gravity models of the southwest Washington margin.…”