SCEC Award Number 16132 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title 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
Other Participants Laura Reynolds (PhD Student)
SCEC Priorities 1a, 2a, 4a SCEC Groups Geology
Report Due Date 03/15/2017 Date Report Submitted 03/14/2017
Project Abstract
 The purpose of this project is to determine if Carpinteria and Goleta Sloughs contain evidence for either 1.) tsunamid or 2.) coseismic subsidence associated with motion along the Pitas-Point Thrust-Ventura Avenue Anticline (PPT-VAA). We have obtained over 75 cores from these two sloughs as well as four other estuaries along the northern Santa Barbara Channel. Our cores reach depths of over 20 m. Although the record from Carpinteria Slough extends to 6.5 ka and the record from Goleta Slough extends to 8.9 ka, 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. Thus, the absence of tsunami deposits is not likely a preservation issue but likely indicates no large tsunamis were created by the PPT-VAA. We also established subsidence rates for Carpinteria (1.2+/-0.4 mm/yr) and Goleta (0.4+/-0.3 mm/yr) Sloughs. Sharp stratigraphic contacts between muds containing high-marsh foraminifera and sands with subtidal mollusks 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. An anomalous sand, but likely not a tsunami, is found in four other estuaries including Goleta Slough at this time.
Intellectual Merit This work directly addresses SCEC priorities by corroborating the record of large earthquakes on the Pitas Point Thrust, and by determining whether the southern California coast may be struck by locally-generated large tsunamis, which have been inferred to result from uplift events on the PPT-VAA during large earthquakes on the underlying PPT and are reported in many modeling studies (Borrero et al., 2001; Ryan et al., 2015). The PPT is one of the largest faults in the Transverse Ranges, falling in the former Ventura Special Fault Study Area (VSFSA). Documenting evidence for tsunami deposits would demonstrate linkage within this major thrust system and provide a test for the opposing structural models of the PPT-VAA. In conjunction with the results of the Ryan et al. (2015) model, our work explicitly tests the Hubbard et al. (2014) structural model for the PPT-VAA. Our work has also contributed to our understanding of the connections between faulting and subsidence in estuaries, large storms that hit California in the past, and general estuarine sedimentation along southern California.
Broader Impacts This grant supported the PhD dissertation of Laura Reynolds and the MS thesis of Michael Bentz. Fourteen other graduate/undergraduate students also helped in the collection of both field data and lab data including four students from under-represented groups. The project also allowed me to make collaborative contacts with researchers at the USGS, San Diego State University, and the University of Northern Arizona. Outreach talks have also been given at the Goleta Public Library and Carpinteria Nature Reserve Docent Training Program.
Exemplary Figure Figure 3. Core logs from Carpinteria Slough illustrating the abrupt subsidence event that occurred at 2.0 ka (thick ~horizontal red line). Inset is a plot of all the radiocarbon ages above (to the right of the vertical line) and below (to the left of the vertical line) within the cores that sample the surface (Reynolds et al., in prep.).
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