Group B, Poster #142, Fault and Rupture Mechanics (FARM)

Quaternary Slope Failure History from Repeated Submarine Landslide Deposits at Cortes Basin, Outer California Borderland

Andrea Fabbrizzi, Jillian M. Maloney, Boe Derosier, Bradley Keith, Sofia T. Quintero, & Hernan Guerrero
Poster Image: 

Poster Presentation

2023 SCEC Annual Meeting, Poster #142, SCEC Contribution #13004 VIEW PDF
Episodic submarine mass transport deposits (MTDs) are identified in high-resolution sub-bottom data collected within the fault-bounded Cortes Basin within the Outer California Borderland (OCB). The identified MTDs are likely associated with intermittent seismicity and/or sea level variations of the late Quaternary. Future MTDs within the OCB have the potential to inundate coastlines via landslide-generated tsunamis, increasing the seismic hazard of the highly populated Southern California Coast. Here, we present a novel high-resolution bathymetric and sub-bottom dataset to map and reconstruct the history of repeated MTDs in the Cortes Basin, located ~170 km offshore San Diego, California. Bo...unded by steep slopes, the fabric of the ~3600 km2 Cortes Basin is aligned NW-SE; a central ridge separates this dual-depocenter basin into East and West Cortes Basins. Our high-resolution bathymetry data reveals deformational morphology in the form of gullies, slide scarps, and new fault segments with evidence of Holocene activity. Additionally, we identified and dated ten repeated MTDs within the sub-bottom data extending across the East and West Cortes Basins, with a recurrence interval of ~84 ka during the last ~760 ka and an estimated total volume of >4 km3 of basinward mobilized sediment. The most recent MTD architecture observed within the West Cortes Basin shows an erosional base truncating the surficial Holocene drape. The thicker proximal deposit relative to the MTD source area is composed of slumps and compressional ridges, and the thinner distal deposit reveals parallel bedding pinching out at the toe scarp. The close spatial correlation between the ten stacked MTDs and the fault segments suggests that the identified MTDs most likely occurred during seismic events within the basin, alternating with the pelagic drape deposited during interseismic phases. Although the mass wasting observed within the Cortes Basin is relatively far from the densely populated coastline of Southern California, it may still pose a tsunamigenic hazard that needs further investigation. Additionally, if the MTDs are linked to seismic events, they could be helpful proxies to inform the seismic history of the relatively understudied OCB.