Timing and Extent of Submarine Landslides in Southern California

Lee, Homa J. (USGS) | Normark, William R. (USGS) | Fisher, Michael A. (USGS) | Greene, H. Gary (Moss Landing Marine Laboratories) | Edwards, Brian D. (USGS) | Locat, Jacques (Laval University)


Submarine landslide deposits occur in many locations throughout the Southern California Borderland and indicate the potential for continued slope failure. Future landslide activity may constitute a direct hazard to offshore facilities and an indirect hazard to coastal communities through landslide-induced tsunamis. Evaluating the risk of these hazards requires information on the scale of landslides that can occur and their recurrence rate. In this study, five mass transport complexes are described and volumes are estimated. Two of these complexes, the Palos Verdes debris avalanche and the Goleta slide contain the remains of many past events. Using dated cores and tracing stratigraphy to nearby ODP borings, we have estimated ages of the most recent failures in the five complexes and some of the ages of earlier failures in the Goleta slide. These results show that the volumes of the failed masses vary over several orders of magnitude with the largest of the masses having volumes on the order of 0.5 km3. The ages of the failures range from a few hundred years to over 100,000 years. The two complexes that show repeated failure represent the largest landslides we evaluated and probably are the largest complexes on the mainland slope in outhern California. We estimate that these large failures on the mainland slope probably reoccur with an interval that has an order of magnitude of 10,000 years.