Sediment offscraping and accretion takes place predominantly by landward-vergent thrusting along most of the Oregon accretionary prism north of latitude 44°50'N. This indicates very low basal shear stress, probably due to near-lithostatic fluid pressure on the décollement horizon. Recent multichannel seismic and sidescan sonar studies have demonstrated the existence of an oblique, basement-involved, left-lateral strike-slip fault, termed the Wecoma fault. It cuts abyssal plain sediments and oceanic basement of the subducting plate. Where the Wecoma fault intersects the wedge thrust front at 45°09'N, accretion to the wedge occurs through an anomalous seaward-vergent thrust. Linear, fault-parallel erosional gullies, which trend obliquely across the slope on the seaward flank of the frontal anticline in the accretionary wedge, are interpreted as marking the surface traces of splays of the Wecoma fault. Data collected during six Alvin dives on and around these gullies demonstrate...