Wide-angle seismic refraction and reflection studies of the northern California and southern Oregon continental margins

Graduation date: 1979Recently obtained airgun-sonobuoy wide-angle refraction and\ud reflection profiles provide data to study crustal velocities and\ud structures along the continental margin of northern California and\ud Southern Oregon.\ud In the thick sedimentary wedge at the base of the continental\ud slope, as many as five distinct layers can be seismically observed,\ud which range in velocity from 2.13 to 3.32 km/sec. The basement\ud layers beneath the wedge are disrupted. The profile which crosses\ud the southeasternmost portion of the Gorda Basin near Cape Mendocino\ud shows evidence of compression at the base of the slope. Velocities of\ud 3.14 to 5.15 km/sec were obtained for this line. Off the central\ud Oregon margin on the abyssal plain near the base of the slope, oceanic\ud layers and 3 overlie a shallow mantle of velocity 7.65 km/sec.\ud Basement velocities average 4.75 km/sec and sediment velocities varied\ud from 1.60 to 2.78 km/sec.\ud The lower slope of the northern California-southern Oregon\ud margin is characterized by rough, folded structures which trend north-south.\ud Little recent sediment cover is seen. A velocity of 2.25 km/sec\ud was obtained for a 520 m-thick surface layer underlain by material\ud with a refraction velocity of 2.68 km/sec. The abyssal plain\ud sediments near Cape Mendocino appear to be in the process of being\ud uplifted and folded into the lower slope, while near Cape Blanco\ud the lower slope displays sediments which abut against the base of the\ud slope below a prominent lower shelf bench.\ud The upper slope shows large anticlinal folds which form the\ud basement of the upper slope basins, particularly beneath the Klamath\ud Plateau off Northern California. Velocities obtained from the\ud sediments of the Klamath Plateau vary from 1.73 to 2.63 km/sec.\ud The inner shelf region is formed by a synclinal basin controlled\ud by an outer continental high which parallels the shelf break.\ud Velocities were studied mainly from refraction arrivals with an\ud assumed surface sediment velocity of 1.66 km/sec. The underlying\ud sediment velocities range from 2.07 to 2.75 km/sec.\ud Evidence of uplift, basement deformation, sediment deformation\ud within structurally controlled basins, compression features, and the\ud north-south trending folds all support an imbricate thrust model\ud for this continental margin