Accretionary prisms form along the landward side of deep- sea trenches in response to offscraping of oceanic sediments during lithospheric subduction. Several interrelated factors influence the evolution of these thick sediment prisms, including sediment composition, physical properties, rate of underthrusting and dewatering and fluid migration within the off-scraped sediment pile. Fluid migration and expulsion play an important role in the mechanical behavior, fluid pressure and lithification of sediments in the deformation zone. Previous research along the Oregon margin has identified significant areas of fluid discharge and venting. The purpose of the present study is to acquire side-scan sonar and multichannel seismic data with which to examine the structural setting of the Oregon margin and the vent locations. An attempt will be made to identify both the source and transport pathways of fluids in the accretionary prism.
