Graduate Thesis Or Dissertation
 

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/sj1396669

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  • The Santa Barbara-Montecito and Goleta basins are structurally continuous fault-controlled Pleistocene basins containing up to 3000 feet (925 m) of marine Pleistocene Santa Barbara Formation which were deposited on previously deformed Sisquoc and older strata. Structures subcropping against the unconformity at the base of the Santa Barbara Formation show that pre-basin deformation was mainly by folding. In addition, high-angle reverse faulting occurred along the Cameros, Goleta, and Modoc faults prior to Santa Barbara deposition in the Goleta basin. These are the oldest faults in the study area. Deposition of the Santa Barbara Formation began less than 1.2 Ma ago. Post-Santa Barbara (post-basin) deformation includes disharmonic folding of incompetent Miocene strata above broad folds in competent Oligocene strata, as displayed in the Elwood oil field and La Goleta gas field, and reverse faulting along several south-dipping faults of large displacement. The More Ranch fault, which juxtaposes Sisquoc and older strata against the Santa Barbara and Pico(?) Formations, displaces a 40,000 year old marine terrace, forms a north-facing eroded fault scarp, and marks the southern edge of the Goleta basin. The fault dips more than 80° south and displays up to a maximum of 2000 feet (610 m) vertical separation. The fault in the area with the largest amount of vertical separation, is the Coal Oil Point fault of post-Sisquoc age. This fault fails to reach the surface even though vertical separation of the Oligocene Vaqueros Formation is as great as 5400 feet (1650 m). Comparison with other faults in the area suggests that this fault belongs to the set of south-dipping, east-trending, Quaternary reverse faults that are characteristic of the coastal basins adjacent to the central Santa Ynez Mountains. All post-basin faults disrupt late Pleistocene strata and are potentially active. Other post-basin faults include the Mesa fault, which may link the More Ranch and Rincon Creek faults, the Lavigia fault which cuts older alluvium, and the San Jose fault which forms a north-facing scarp in late-Pleistocene fanglomerate. Distribution of aftershocks and focal mechanism solutions of the 1978 Santa Barbara earthquake suggest a gently north-dipping fault plane which would be unrelated to any of the faults exposed at the surface in the study area. However, the linear pattern of aftershock epicenters is parallel to the Mesa and Mission Ridge- Arroyo Parida faults; if the alternate south-dipping nodal plane is the correct solution then the earthquake could have originated on a member of the south-dipping fault set.
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