Modern Turbidite Systems Along the Northern California Continental Margin and Their Holocene Earthquake Triggering History from the San Andreas Fault

Nelson, C. Hans¹, Chris Goldfinger², Julia Gutierrez Pastor¹, Ann Morey Ross², Eugene Karabanov³ (1) University of Granada, Granada, Spain (2) COAS Oregon State University, Corvallis, OR (3) University of South Carolina, Columbia,

Numerous turbidite systems along the northern California continental margin are influenced by the San Andreas Fault (SAF) that parallels the coast near San Francisco Bay and underlies the continental margin. Multiple tributary slope canyons and proximal channels join downstream into large channels, and all systems are dominated by the deposition of turbidite silt and sand beds. Synchronous SAF triggering of many turbidity currents by great earthquakes along ~ 400 km of the margin is suggested by (1) 14C ages, (2) channels below tributary canyon confluences that are characterized by single turbidite beds with multiple coarse-grained sediment pulses differentiated mineralogically as sourced by the tributary canyons, and (3) gamma density and high-resolution magnetic susceptibility log signatures of turbidites that correlate down individual channels and between channels along the margin. The most complete and reliable turbidite record is found in Noyo Channel where the canyon head source of channel turbidites is directly underlain by the SAF and where the youngest five turbidite ages agree with the land paleoseismic record. In Noyo Channel, the turbidite paleoseismic record for 14 events on the northernmost SAF during the past 2600 cal. yr BP is based on two methods: 1) hemipelagic sediment thickness (H) between turbidites (H/sedimentation rate = recurrence time), and 2) 14C age differences between turbidites. The average recurrence time between turbidites is ~ 220 yr with most of the recurrence times between 200 to 250 years. The minimum recurrence times are ~ 140 (based on 14C) to 180 yrs based on H) and the maximum time is ~ 300 (H) to 350 (14C) yrs.