Displacement direction and 3D geometry for the south-directed North Channel – Pitas Point fault system and north-directed ramps, decollements, and other faults beneath Santa Barbara Channel.

Christopher C. Sorlien, Craig Nicholson, Richard J. Behl, & Marc J. Kamerling

Submitted August 15, 2016, SCEC Contribution #6839, 2016 SCEC Annual Meeting Poster #007

We use abundant seismic reflection data to interpret 3D fault geometry in the upper 5 to 8 km beneath Santa Barbara Channel and use dated and correlated seismic stratigraphy to study 3D fold geometry and its changes through Quaternary time.

A set of north-directed (top-to-north) faults underlie much of Santa Barbara Channel. The offshore S-dipping offshore Oak Ridge fault merges westward with a blind fault forming a kinematically-continuous 100+ km-long system. Horizontal N-directed decollements intersect this broader Oak Ridge fault system (ORFS) at 6 to 7 km depth. The down-to-north tilting southern margin of Santa Barbara basin may be a forelimb above the ORFS, instead of, or in addition to, being a backlimb above the Channel Island thrust.

North Channel–Pitas Point fault strands dip north with S-directed motion across 120 km from near Ventura to west of Point Conception. This fault system is mostly blind and associated with broad forelimb tilting. The rate of tilting decreases from east to west but is relatively uniform in any one location since 1.8 Ma.

The geometry is complex. The 60 km-long offshore Pitas Point fault strand continues farther east onshore as the Ventura fault. To the west, 10 km west of UCSB, this NNE-dipping strand terminates into N-dipping strands, forming a 25° bend, the Gato Canyon segment boundary. Although N-dipping fault strands continue west of this segment, the lower, southern faults die out offshore Gaviota to be replaced by the north-directed Hondo fault, linked southward by a subhorizontal decollement to a the western ORFS. Blind N-dipping fault strands associated with a tilting forelimb re-appear west of Gaviota and continue 30 km farther to west of Pt. Conception. This segment may be kinematically linked to a southern strand of the right-lateral Hosgri fault.

Folding between the Gato Canyon segment boundary and Pitas Point is partly accomplished by the Pitas Point strand together with a stack of flatter N-dipping faults and the large S-dipping Padre Juan (Hobson) blind fault. The Padre Juan fault is interpreted for 30 km west of Pitas Point. Strands of the N-dipping Red Mountain fault are also mapped 50 km between Carpinteria and the Gato Canyon segment boundary. The continuity of the progressive tilting above the western 50 km of the Pitas Point fault suggests continuity of blind (oblique) thrust displacement. It exhibits no evidence for a sea floor fault rupture for at least the last half million years in that part.


Citation
Sorlien, C. C., Nicholson, C., Behl, R. J., & Kamerling, M. J. (2016, 08). Displacement direction and 3D geometry for the south-directed North Channel – Pitas Point fault system and north-directed ramps, decollements, and other faults beneath Santa Barbara Channel. . Poster Presentation at 2016 SCEC Annual Meeting.


Related Projects & Working Groups
Unified Structural Representation (USR)