Shelf evolution along a transpressive transform margin, Santa Barbara Channel, California

Abstract

High-resolution bathymetric and seismic reflection data provide new insights for understanding the post-Last Glacial Maximum (LGM, ca. 21 ka) evolution of the ~120-km-long Santa Barbara shelf, located within a transpressive segment of the transform continental margin of western North America. The goal is to determine how rising sea level, sediment supply, and tectonics combine to control shelf geomorphology and history. Morphologic, stratigraphic, and structural data highlight regional variability and support division of the shelf into three domains. Ages and rates of deformation are derived from a local sea-level-rise model that incorporates an inferred LGM shoreline angle and the LGM wavecut platform. Post-LGM slip rates on the offshore Oak Ridge fault are a minimum of 0.7 ± 0.1 mm/yr. Slip rates on the Pitas Point fault system are a minimum of 2.3 ± 0.3 mm/yr near Pitas Point, and decrease to the west across the Santa Barbara Channel. Documentation of fault lengths, slip rates, and rupture modes, as well as potential zones of submarine landsliding, provide essential information for enhanced regional earthquake and tsunami hazard assessment.

Scales of Stress Heterogeneity Near Active Faults in the Santa Barbara Channel, Southern California

“…The Santa Clara Avenue oil field is a stratigraphically trapped reservoir (DOGGR, ) and therefore does not contain any major structural trends with which the orientation of maximum compressive stress can be correlated. However, the West Montalvo oil field wells target the E‐W trending Montalvo anticline, which is bound to the north by a steeply SE‐dipping, NE‐striking segment of the Oak Ridge Fault, and is cut by a steeply N‐dipping, NE‐striking growth fault called the Montalvo fault (Figure ) (Johnson et al, ; Yeats, ).…”

“…Ridge Fault, and is cut by a steeply N-dipping, NE-striking growth fault called the Montalvo fault ( Figure 8) (Johnson et al, 2017;Yeats, 1976).…”

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

“…The North Channel (NC) fault, also referred to as the North‐Channel Pitas‐Point fault and the North‐Channel Slope fault system, is the “master” west‐striking, south‐dipping, blind thrust fault system that cuts across the shelf (to the east) and slope (to the west) along the mainland SBC coast (e.g., Greene et al, 2006; Heck, 1998; Johnson, Hartwell, et al, 2017; Sorlien & Nicholson, 2015), forming the tectonic boundary between an actively growing uplift to the north and the Santa Barbara‐Ventura basin to the south. This blind fault system is overlain by a regional south‐dipping monocline and a complex upper plate cut by numerous south‐ and north‐dipping splays and associated smaller‐scale folds (Johnson, Hartwell, et al, 2017). Notable upper plate structures include the Red Mountain (RM) fault, Rincon anticline, Rincon Creek fault, Molino anticline, Point Conception anticline, Government Point syncline, and Hondo anticline (Figure 2a; Fischer, 1998; Johnson, Hartwell, et al, 2017; Novoa, 1998).…”

“…This blind fault system is overlain by a regional south‐dipping monocline and a complex upper plate cut by numerous south‐ and north‐dipping splays and associated smaller‐scale folds (Johnson, Hartwell, et al, 2017). Notable upper plate structures include the Red Mountain (RM) fault, Rincon anticline, Rincon Creek fault, Molino anticline, Point Conception anticline, Government Point syncline, and Hondo anticline (Figure 2a; Fischer, 1998; Johnson, Hartwell, et al, 2017; Novoa, 1998). The uplifting Channel Islands platform forms the southern margin of the Santa Barbara basin.…”

“…See Napier et al (2019) for a detailed overview of watershed locations. There is minimal sediment cover on the middle to outer shelf between Goleta and Point Conception (Figure 5 in Johnson, Hartwell, et al, 2017), and the sediments on the slope in this region were probably sourced primarily by streams from the SYM that flowed across and (or) fed the shelf during Pleistocene sea‐level lowstands and regressions (e.g., Napier et al, 2019; Waelbroeck et al, 2002).…”