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Pacific Coastal and Marine Science Center

PCMSC Seminar Series

Upcoming Seminar

Chris Sorlien
Earth Research Institute, UC Santa Barbara

Friday, April 17, 2015, 11:00 am

Neogene fault evolution, offshore south-central California using geology and seismic stratigraphy

with contributions from Richard Behl, Craig Nicholson, Nelson Doris, Courtney Marshall, James Kennett, and Marc Kamerling

Sample diagrams from Chris' talk.

Abstract:
Faults offshore south-Central California and in northern Santa Barbara Channel present earthquake hazards to coastal cities and facilities. This includes the offshore 120 km of the (oblique) blind thrust North-Channel-Pitas Point system, thought by some to be capable of M8.0 earthquakes. These faults and associated folds have accommodated oblique NNE-SSW contraction for the last ~5 million years. Faults in Santa Barbara Channel strike E-W, and deformation is a combinations of thrusting and left-lateral displacement. Faults in offshore south-central California strike NNW-SSE and deformation is a combination of thrusting and right-lateral displacement. These two fault domains intersect and interact in the area offshore Pt. Arguello. These faults were mostly present earlier, and experienced oblique extension between ~19 and ~5 million years ago. Thus, the currently active faults are reactivated. The pre-existing structure results in strike-slip motion occurring on faults with surprising geometry. Moderately-dipping strike-slip fault segments are relatively common in offshore southern and central California. For example, the right-lateral Hosgri fault dips east less than 30 degrees at depths below 1 km, to at least 2 km, as imaged on profiles from 3D seismic reflection data. The northernmost of these profiles is 15 km south of the Diablo Canyon nuclear generating station. The deep fault there is kilometers east of the projection of the vertical shallow fault.

Our regional seismic stratigraphic correlations are constrained by the geology sampled in petroleum test wells and our own piston cores. These piston cores sampled seafloor outcrops in central Santa Barbara Channel. Our group used biostratigraphy, oxygen isotopic stratigraphy, and tephrochronology of the 639 ka Lava Creek ash to produce a precise seismic stratigraphic age model back to 740,000 years. Older control from paleontology on sea floor and well samples includes a ~1 Ma horizon from Santa Barbara Channel, a ~1.2 million year-old horizon from Ocean Drilling Program site 1017, and the 1.8-1.9 million year-old top Lower Pico.

 

See a list of all Seminars previously presented.


Directions and Parking

Street map of our location.
[Larger version]

From the San Francisco Bay Area:
Take your favorite highway to Hwy 17 South to Hwy 1
At the Hwys 17+1 merge, keep right
Follow signs to “Hwy 1 North, Half Moon Bay, UC Santa Cruz”
Stay on Hwy 1 North (keep in right-most lanes)
Hwy 1 is also named Mission St. — Follow Mission for about 2 miles
At the Western Drive stop light, turn left onto Western Drive
The building right in front of you is the
USGS Pacific Coastal and Marine Science Center
2885 Mission St. Extension
at the intersection of Western and Mission St. Extension

From the south coast:
Take Hwy 1 North to west Santa Cruz
At the Western Drive stop light, turn left onto Western
The building right in front of you is the USGS Pacific Coastal and Marine Science Center, at the intersection of Western and Mission St. Extension

From the north coast:
Take Hwy 1 South to west Santa Cruz
At the Western Drive stop light, turn right onto Western
The building right in front of you is the
USGS Pacific Coastal and Marine Science Center
2885 Mission St. Extension
at the intersection of Western and Mission St. Extension

Parking:
You may park in the parking lot located on the NE corner of Western Drive and Mission St. Extension
Limited parking is available along Mission St. Extension and along Natural Bridges Drive
Entrance to PCMSC is at 2885 Mission St. Extension (small green star with arrow, on the map), at the intersection of Western and Mission St. Extension

Photograph of Natural Bridges, photo by Laura Torresan. 

Schedule

Fri., April 17, 2015, 11:00 am

Chris Sorlien

UC Santa Barbara

See a list of all Seminars previously presented.

 

 

 

How to find our Seminar Room

Schematic shows how to get to the PCMSC seminar room.

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URL: http://walrus.wr.usgs.gov/seminar/
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Page Last Modified: 24 March 2015 (lzt)