Velero Basin

Velero Basin, Outer California Borderland: mapping of submarine mass transport complexes using new high-resolution marine geophysics

https://doi.org/10.7284/909885 

Abstract - Seafloor slopes are shaped by the gravity-driven sediment transport process known as submarine mass wasting, often triggered by seismic activity along tectonically active margins. Mapping and understanding the dynamics of mass wasting is essential for geohazard assessments and tsunami modeling. In the tectonically active California Continental Borderland, mass wasting commonly occurs along strike-slip faults with vertical components, which induce slope oversteepening and initiate coseismic failure. In the Outer California Borderland, we mapped two distinct mass transport complexes (MTCs) in Velero Basin using high-resolution geophysics. The southern MTC consists of overlapping debris lobes and rockfalls on the basin floor. The northern MTC features a strike-continuous scarp along the middle slope, three scarps at the lower slope, creating a staircase-like slope profile and suggesting multi-failure episodes along weak layers. High-resolution sub-bottom data show that recent mass transport deposits (MTDs) are infilling accommodation created by faulting, while multichannel seismic profiles reveal deeply buried submarine landslides. The mass wasting history includes a >200 m thick slide within the late Miocene to Pliocene succession (>3.7 Ma), a ~30 m thick MTD from the early Pleistocene (~1.2 Ma), and recent MTDs up to 60 m thick on the basin floor. Stacked MTDs indicate long-term mass wasting, likely linked to earthquakes during both the late Miocene to early Pliocene oblique-extensional phase and the early Pliocene to Recent tectonic inversion. The active Ferrelo fault zone, bounding the Santa Cruz, San Nicolas, Tanner, Cortes, and Velero basins, may trigger simultaneous multi-basin failures, increasing seismic and tsunami hazards for Southern California’s coastal areas.