Structural Controls on Slope Failure Within the Western Santa Barbara Channel Based on 2‐D and 3‐D Seismic Imaging

Abstract

The Santa Barbara Channel, offshore California, contains several submarine landslides and ample evidence for incipient failure. This region hosts active thrust and reverse faults that accommodate several mm/yr of convergence, yet the relationships between tectonic deformation and slope failure remain unclear. We present 3‐D and 2‐D multichannel seismic reflection (MCS) data sets, multibeam bathymetry, and chronostratigraphic constraints to investigate the controls on slope failure. Splay faulting along the North Channel Deformation Trend (NCDT) coincides with a distinct zone of compressional uplift and onlapping of steeply dipping Quaternary strata. The NCDT is spatially correlated with seafloor fissures, and 3‐D seismic analyses reveal an intricate system of en echelon reverse faults that offset sediments younger than ~25 ka. Localized uplift zones are located between faults, one of which underlies the Gaviota landslide headscarp. We observe a direct relationship between slope failure and along‐strike variations in the tectonostratigraphic framework. Based on geophysical properties at Ocean Drilling Program (ODP) Site 893, we predict a trend in compaction and porosity reduction in the basin that drives pore fluids up‐dip, toward the zone of onlap above the NCDT, thus reducing slope stability. This interplay between tectonic, sedimentary, and fluid‐flow processes along the NCDT has created a confluence of preconditioning factors, with Gaviota and Goleta landslides being distinguished from the surrounding slopes by their position above the NCDT. The distribution of seafloor fissures suggests sections of the slope remain unstable and are prone to future landsliding. These results provide insights into the processes and 3‐D feedbacks that lead to slope instability along other convergent margins.

A Comprehensive Assessment of Submarine Landslides and Mass Wasting Processes Offshore Southern California

“…(2006) used surficial geomorphology from multibeam bathymetry to identify distinct lobes; the earliest (now buried) Goleta slide is as old as 200 ka (as derived from seismic imaging and sedimentation rates), but the three most recent slides (those included with our compilation) have been dated at 6–8 ka, 8 ka, and 10 ka (Fisher et al., 2005; Greene et al., 2006). The smaller (0.01–0.2 km 3 ) neighboring Gaviota landslide occurred due to similar processes (tectonic compaction, porosity reduction) as the Goleta complex (Fisher et al., 2005; Greene et al., 2006; Kluesner et al., 2020).…”

“…We make inferences about sediment thickness and shear strength based on proximity to sediment sources and Quaternary faults, but do not directly measure or model these parameters. Additionally, processes related to subsurface fluids, gas, and seeps, which are prominent in several regions including Santa Barbara Basin (Kluesner et al., 2020), were not analyzed in this study and may provide further insights into the slide preconditioning and triggering processes. Finally, while several studies have noted the tsunami risk from Borderland slides (Borrero et al., 2004; Brothers, Andrews, et al., 2019; Brothers, Maier, et al., 2019; Fisher et al., 2005; Greene et al., 2006; Legg & Kamerling, 2003; Lee et al., 2009; K. J. Ryan et al., 2015), few have been quantitatively modeled, including the newly discovered San Nicolas slide.…”

“…Submarine landslides (or "slides") offshore southern California region have been studied for decades due to their tsunamigenic potential and risk to dense coastal populations (Borrero et al, 2004;Brothers et al, 2019a;Fisher et al, 2005;Greene et al, 2006;Kluesner et al, 2020;Lee et al, 2009;Legg & Kamerling, 2003; K. J. Ryan et al, 2015).…”

“…These new data provide an opportunity to systematically map and characterize submarine mass transport features offshore of southern California from Point Conception in the north to the United States‐Mexico Border in the south (Figure 1). The increase in available high‐quality, high‐resolution bathymetric and sub‐bottom data has also led to new local characterizations of submarine landslides offshore of southern California, including analysis of the Santa Cruz Basin slide complex (Brothers, Maier, et al., 2019), the Santa Barbara Basin slides (Fisher et al., 2005; Greene et al., 2006; Kluesner et al., 2020), and the Palos Verdes debris avalanche (Locat et al., 2004; Normark et al., 2004).…”

“…Submarine landslides (or “slides”) offshore southern California region have been studied for decades due to their tsunamigenic potential and risk to dense coastal populations (Borrero et al., 2004; Brothers et al., 2019a; Fisher et al., 2005; Greene et al., 2006; Kluesner et al., 2020; Lee et al., 2009; Legg & Kamerling, 2003; K. J. Ryan et al., 2015). Starting around 1970, investigators of seminal marine geophysical and sediment sampling surveys offshore southern California recognized that mass wasting is an important sedimentary process throughout the region and documented the existence of fairly large zones of seafloor covered in slide debris (Barnes, 1970; Felsher, 1971; Field & Edwards, 1980; Field & Richmond, 1980; Fisher et al., 2005; Gorsline & Barnes, 1972; Greene et al., 2006; Nardin, Edwards, & Gorsline, 1979; Nardin, Hein, et al., 1979; Normark & McGann, 2004; Normark et al., 2004; Schwalbach & Gorsline, 1985; Teng & Gorsline, 1989).…”