Tsunamogenic landslides and marine paleoseismology: applications of the submerged marine terrace record, Santa Catalina Island, Southern California Borderland

Abstract:

Transpressional structures related to deformation along the Greater San Andreas Fault are largely responsible for creating the complex morphology and steep topography in the Southern California Borderland. The numerous anastamosing strike slip faults dissecting the area are responsible for creating its complex morphology and present a seismic hazard to nearshore communities. Submarine slope failures tend to nucleate on faulted steep topography and could generate a tsunami dangerously close to densely populated urban areas. We present evidence for a tsunamogenic landslide originating from Catalina Island and directed toward the mainland. Radiometric dates of fossils collected during coring cruises and ROV dives during 2014-15 provide age control for high-resolution 2D and 3D seismic reflection profiles collected near Santa Catalina Island and Pilgrim Banks. These refine our established sequence stratigraphic subsidence history for Catalina Island, and enable us to constrain the timing of the landslide deposit, as well as other landslide deposits and faults. Although the slide is pre-Holocene, the threat of another tsunamogenic landslide directed at urban southern California is increased by gradual tilting of the Catalina block toward mainland California. Our study demonstrates that investigations using a combination of bathymetry, 2D and 3D MCS can be used to map submerged marine terrace deposits and those can then be used as offset markers for paleoseismic investigations. The subsided marine terrace record has potential paleoseismologic applications on over 20 submerged seamounts and islands in Southern California, as well as applications in providing constraints on Quaternary sea level history.