Abstract

The Santa Barbara Channel basin, located in southern California, is undergoing significant shortening. We use contour and axial surface maps of several horizons and balance regional cross sections through the eastern and western Santa Barbara Channel, as well as structural profiles and surface restoration techniques, to analyze how the subsurface structures in this basin accommodate the deformation. Reflection seismic profiles show that some of the mapped structures are active (e.g. the Oak Ridge, the Blue Bottle, the Pitas Point, the Dos Cuadras, the Carpinteria and the Santa Rosa trends) and accommodate a large part of the shortening, whereas others are completely inactive (e.g. the Western Deep trend).

Restoration of seismic profiles shows that structures in the basin grow by kink-band migration. In cross sections, we interpret that to the east, there are mainly two levels of faulting. The Oak Ridge trend develops above the deeper one, whereas the Dos Cuadras, the Pitas Point, the Carpinteria and the Blue Bottle trends develop on the shallow one. To the west, we interpret the existence of three levels of faulting. A mid-crustal detachment is the deepest one, the Blue Bottle and the Western Deep trends are developed above the shallowest one. The Santa Rosa trend is growing above an intermediate one.

The axial surface and contour maps suggest that the Blue Bottle and Pitas Point trends end progressively to the west, accommodating an average of 2 to 4 km of shortening. The Oak Ridge trend terminates at a tear fault south of the Santa Barbara city. This fold accommodates about 11 km of slip. We show, using map view restoration, that slip involved in this trend is transferred to the west through a mid-crustal bedding parallel detachment fault. The Dos Cuadras trend extends beyond the mapped area both to the east, where it becomes the Ventura anticline, and to the west. We determine that the Dos Cuadras and Carpinteria trends accommodate about 11 km of shortening. The Santa Rosa trend is a new mapped trend in the southwestern area of the basin.