Stratigraphic and structural controls on submarine mass wasting in Velero Basin, Outer California Borderland

Andrea Fabbrizzi, & Jillian M. Maloney

Awaiting Publication May 31, 2026, SCEC Contribution #15049

Submarine mass wasting in the active California Continental Borderland is controlled by strike-slip tectonics and stratigraphic heterogeneity, producing recurrent slope failure and mass transport deposits (MTDs) in structurally confined basins. In the Velero Basin, Outer California Borderland (OCB), new high-resolution geophysical data reveal two adjacent but morphologically distinct mass transport complexes (MTCs), reflecting different failure styles. The southern MTC is characterized by canyon-controlled sediment transport and deposition of overlapping debris lobes and rockfalls on the basin floor. The northern MTC shows a stepped slope profile defined by multiple scarps, indicating basinward-progressive failure and structural control by faulting and mechanically weak stratigraphic horizons. Seismic stratigraphy documents multiple MTDs spanning Late Miocene to Recent, including a > 200 m-thick Late Miocene–Pliocene slide (>3.7 Ma), a ~ 35 m Early Pleistocene deposit (~1.3 Ma), and recent events up to ~72 m thick on the seafloor. A regionally continuous reflector, interpreted as a turbidite (~721.4 ± 6 ka), likely acted as a weak layer facilitating recent mass wasting. A coeval but distinct turbidite is identified in the adjacent Cortes Basin. The correlation between these deposits suggests potential synchronicity in MTD emplacement, implying that large-magnitude earthquakes can trigger extensive slope failures across the OCB.

Key Words
Mass wasting, Velero Basin, Outer California Borderland, Seafloor morphology, High-resolution geophysics, MTDs

Citation
Fabbrizzi, A., & Maloney, J. M. (2026). Stratigraphic and structural controls on submarine mass wasting in Velero Basin, Outer California Borderland. Marine Geology, (awaiting publication). https://doi.org/10.1016/j.margeo.2026.107822.