SCEC Award Number 15156 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title Collaborative research: Stratigraphic Changes within Carpinteria and Goleta Slough Estuaries: A signal of Great Earthquakes on the Pitas Point Thrust
Investigator(s)
Name Organization
Alexander Simms University of California, Santa Barbara Thomas Rockwell San Diego State University Robert Peters San Diego State University
Other Participants Laura Reynolds, Michael Bentz, Yuval Levy
SCEC Priorities 1a, 2a, 4a SCEC Groups Geology
Report Due Date 03/15/2016 Date Report Submitted 03/14/2016
Project Abstract
 The purpose of this project is to determine if Carpinteria and Goleta Sloughs contain evidence for either 1.) a tsunami or 2.) coseismic subsidence associated with motion along the Pitas-Point Thrust-Ventura Avenue Anticline (PPT-VAA). We have obtained over 50 cores from the two sloughs reaching depths of over 20 m. The record from Carpinteria Slough extends to 6.5 ka and the record from Goleta Slough extends to 8.9 ka. However, we have failed to find evidence for tsunami deposition. The identification and preservation of a large storm deposit from the great 1861-1862 storm suggests that Carpinteria Slough is capable of recording marine-sourced events and thus the absence of tsunami deposits is not a preservation issue but likely indicates no large tsunamis were created by the PPT-VAA. Carpinteria Slough is subsiding at a rate of 1.2+/-0.4 mm/yr and Goleta Slough is subsiding at a rate of 0.4+/-0.3 mm/yr. Sharp stratigraphic contacts with high-marsh foraminifera above and sub-tidal sands below suggest the subsidence may be controlled by coseismic events within Carpinteria Slough. The most recent event at 1.9 ka occurred at the same time as motion along the Pitas-Point Thrust. A similar contact is found at the same time within Goleta Slough.
Intellectual Merit This project has shown that co-seismic subsidence is not confined to estuaries along subduction zones but along estuaries also found in other active margin settings. It has evaluated the tsunami hazards of the Pitas-Point-Ventura Avenue Anticline and quantified subsidence in two fault-bound estuaries (an indirect measure of fault motion along the smaller Rincon Creek and More Ranch Faults).
Broader Impacts This project provides data directly for two graduate students at UCSB (one PhD dissertation and one MS thesis). It has also given valuable field experience to three other graduate students at UCSB as well as two other under-graduate students at UCSB. It has helped our group better develop our coring methods. The project is important for the communities along the northern Santa Barbara Channel as it better defines the natural hazards associated with earthquakes in the region.
Exemplary Figure Core description and fence diagram through Carpinteria Slough (A) illustrating the sharp contacts between sedimentary facies. (B) Core photograph of sharp contact between a buried marsh surface and subtidal sand in core CS13-02 from Carpinteria Slough.