Three-Dimensional Seismic Mapping Around Ocean Drilling Program Leg 167 Site 1019 (Site Survey Ca-1): Implications for Sedimentation, Deformation and Evolution of the Eel River Basin

The Eel River forearc basin is located at the southern termination of the Cascadia subduction zone and extends onshore southeast of Eureka, California for 50 km. Offshore, it is up to 100 km wide and trends parallel to the continental margin for 200 km to Cape Sebastian, Oregon. The basin has been complexly deformed by the interacting tectonic forces of: a) subduction of the Gorda plate beneath the North American plate; b) northward migration of the Pacific plate along the San Andreas fault zone; c) extension of the Basin aod Range; and, d) clockwise rotation of the Willamette region. The thesis area, Site CA-1. is located along the edge of the continental slope within the northern Eel River basin and was selected to be drilled as part of the Ocean Drilling Program (ODP) Leg 167. Twenty high-resolution single- and four-channel seismic reflection lines were acquired during two separate site surveys over an area of approximately 400 km2 at Site CA-1. These data were processed and geologically significant reflectors traced throughout the basin to provide a three-dimensional mapping of the subsurface. The two-dimensional processed seismic sections and three-dimensional maps are the basis for interpretation of tectonic forces within the Eel River basin for this thesis. Current literature indicates that changes in the tectonic character of the southern Cascadia subduction might be occurring. These changes include the cessation of subduction of the southern Gorda plate, the continued northward migration of the Mendocino triple junction and the development of a new transform fault between the Gorda and Pacific Plates (Gorda Fault Zone). If this is the case, then evidence for these changes should be evident in the data from Site CA-l. This thesis attempts to address these issues and makes some predications of the future of the southern Cascadia subduction zone