3D characterization of fluid-flow within the western Santa Barbara Channel

Abstract:

3D seismic-reflection volumes, high-resolution sparker profiles, and multibeam bathymetry are used to map substrate fluid migration within the hydrocarbon-rich northern slope of the western Santa Barbara Channel (SBC), offshore California. This seismically active region hosts Goleta and Gaviota submarine landslides, seafloor fissures, and seafloor seepage features (e.g. pockmarks). Within the 3D volumes neural-network attribute flows are used to map out probable fluid-migration pathways. When compared to mapped horizons and fault attribute results, this reveals the 3D relationship between fluid-flow, structure, and stratal geometry. High-resolution sparker profiles reveal details in the shallow substrate and provide a tie between seafloor seepage features imaged on the seafloor and fluid-pathways imaged within the lower resolution 3D volumes. Sparker profiles tied to ODP site 893 provide shallow lithology and age control. The results indicate that fluid migration at depth is largely controlled by the North-Channel Deformation Trend (NCDT) located above the North Channel thrust fault. Folding along this deformation zone has created multiple anticlinal structures that focus and trap fluids, and multiple en-echelon splay faults that bound the small anticlines appear to act as both sealing and leaking faults, some of which supply fluids to the shallow subsurface. Sparker results also suggest up-dip fluid migration occurs from gas-charged sediments that onlap the NCDT, likely driven by compaction and porosity reduction. Spatial correlation of probable substrate fluid migration with existing slope failures suggests fluid flow within SBC plays a critical role in slope stability and is likely a preconditioning factor. These results suggest portions of the slope along the NCDT are likely at risk for future slope failure, especially along the western edge of the Goleta headscarp where extensive seepage is actively occurring.