Fluid flow and deformation at an active continental margin: The Eel River Basin, California

This dissertation addresses how active fluid flow and recent deformation are related to submarine morphology in the offshore Eel River basin along the northern California continental margin. The Eel River basin is an ideal location to study fluid flow and deformation because it is tectonically active, generates hydrocarbons at depth, and experiences rapid sediment loading. Five seismic reflection surveys of varying frequencies are integrated with high-resolution multibeam bathymetry and side-scan sonar surveys to better understand the relationship between subsurface fluids, structure, and seafloor morphology. Two remotely operated vehicle cruises provide a means for groundtruthing, with dive targets based on geophysical observations.; Abundant evidence for subsurface fluids and fluid-related surface morphology exists in the Eel River basin. Thousands of pockmarks, seabed craters that serve as proxies for fluid explusion, occur on the upper continental margin and occur in three size classes from <10 m to 250 m diameter. Pockmarks are <1500 years old, and probably form episodically and catastrophically. An active pockmark shows vigorous gas escape from the crater center. Other seafloor gas vents are associated with the crest of an exposed anticline on the slope and high-angle subsurface faults imaged in seismic reflection records. Not all venting is morphologically expressed.; Recent deformation on the continental shelf is expressed along two east-west-trending narrow (<3 km wide) zones of high-angle deformation that exhibit possible left-lateral oblique-slip motion. Near the surface, both deformation zones are inclined toward the north. Deformation on the continental shelf appears to have changed from northwest-trending, large (>3 km wavelength) open folds, to high-angle faulting in the late Pleistocene. The high-angle faults appear to reach the seafloor. Although offset along the high-angle deformation zones diminishes seaward, the trends of both deformation zones continue as topographic lineaments onshore. The change in deformation type and structural trend on the shelf may be related to the northward migration of the Pacific plate and the Mendocino triple junction.