3D insights into active deformation, stratigraphic architecture, and submarine slope failure in the Santa Barbara Channel, southern California

Jared W. Kluesner, Daniel S. Brothers, Alexis Wright, & Samuel Johnson

Submitted August 15, 2018, SCEC Contribution #8659, 2018 SCEC Annual Meeting Poster #248

Multiple submarine landslides, including the Gaviota (0.01 – 0.02 km3) and Goleta landslide complexes (3 – 4 km3) have been documented along the slope of the seismically active Santa Barbara Basin, however the preconditioning factors leading to slope failure are still poorly understood in this region. Past studies utilized 2D seismic reflection datasets to analyze the regional framework geology, however these datasets were insufficient to characterize the complex nature of active faulting and folding that is possible with 3D seismic data. In this study, we integrate 3D multichannel seismic (MCS) reflection volumes and newly–collected high-resolution 2D MCS, CHIRP, and multibeam bathymetry datasets to analyze the relationships between deep structure, near-surface deformation, stratigraphic architecture, fluid-flow pathways and submarine slope failure. The 3D seismic volumes show that the Pitas Point Fault Complex (PPFC) controls the shallow deformation observed beneath the Gaviota and Goleta landslide complexes, and a seafloor fissure (incipient failure) located between the two landslides. A series of steeply dipping thrusts within the PPFC underlies the Goleta landslide complex, where the faults extends to within a few hundred meters of the seafloor near the shelf break and headwall scarp. To the west near the Gaviota landslide, high-resolution MCS data show that the shallow portion of the PPFC is composed of a previously undocumented network of en echelon faults striking ~25° counterclockwise to the dominant structural grain of the region. Within this system of shallow faults is a locally uplifted zone of fault-propagation folding beneath the Gaviota slide headwall. Analogous patterns of deformation are identified beneath adjacent sections of intact slope, suggesting these areas may be preconditioned for failure. We present a preliminary model for differential compaction between the slope and basin that induces a lateral pressure gradient and updip migration of fluids, which creates a mid-slope zone of reduced shear strength. The model explains the positioning of the Gaviota slide and adjacent incipient failures (tension fissures), and suggests that sections of the adjacent intact slope are likely to destabilize during seismic shaking.

Key Words
submarine landslide, thrust fault, convergence, slope stability

Kluesner, J. W., Brothers, D. S., Wright, A., & Johnson, S. (2018, 08). 3D insights into active deformation, stratigraphic architecture, and submarine slope failure in the Santa Barbara Channel, southern California. Poster Presentation at 2018 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology