SCEC Award Number 12120 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title Collaborative research: Documentation of Tsunami Deposits in the Carpinteria Estuary: A signal of Great Earthquakes on the Pitas Point Thrust
Investigator(s)
Name Organization
Thomas Rockwell San Diego State University Robert Peters San Diego State University Bruce Jaffe United States Geological Survey Bruce Richmond United States Geological Survey Mary McGann United States Geological Survey Stephanie Ross United States Geological Survey Rick Wilson California Geological Survey Eileen Hemphill-Haley Consultant
Other Participants One undergraduate or graduate student as field assistant / researcher
SCEC Priorities 2a, 1a, 4a SCEC Groups Geology, USR, Seismology
Report Due Date 03/15/2013 Date Report Submitted N/A
Project Abstract
 The purpose of our project was to begin the search for tsunami deposits at Carpinteria Salt Marsh that could be the result of great earthquakes on the Pitas Point Thrust system. Towards that end, we collected seven cores from the marsh in 2012, with the longest complete core to 3.7 m depth. Radiocarbon analysis from two of the cores indicates that subsidence is occurring, and the accompanying sedimentation rate is about 2 m per millennium. Faunal analysis of the shallow (< 1 m) cores indicates the absence of offshore foraminifera and diatoms for the past few hundred years of section. Thus, the microfaunal results do not support the interpretation that a distinctive sand layer is the result of a tsunami from the 1812 earthquake, although these results are not definitive. Deeper cores were drilled after the faunal analyses were complete, so analyses of the deeper strata remain for the future. In the deeper cores, there is not an obvious tsunami sand that corresponds with the approximate time frame of the most recent Pitas Point terrace uplift event (700-800 years BP), although there is a sand with an abrupt lower contact that falls within the correct timeframe and may be of tsunami origin. Further microfauna analysis will determine if offshore species are present, and whether this sand could be the result of tsunami.
Intellectual Merit This research contributes to understanding and quantifying the earthquake hazard of a major thrust fault in the Transverse Ranges, the Pitas Point-Ventura thrust. SCEC-funded work indicates that uplift from past earthquakes has resulted in as much as 8-9 m, and probably involve rupture of multiple faults. Scaling relationships suggest earthquakes in the M8 range, larger than generally considered for the Transverse Ranges. The focus of this project is specifically to search for evidence that these large offshore uplifts produced tsunamis that may have struck the Santa Barbara coast within minutes of the earthquake itself.
Broader Impacts Supported a graduate student field assistant. Used the uplifted Holocene terraces and subsidence in Carpinteria as a teaching laboratory for my neotectonics class at SDSU. This has led to a broader collaboration with the UCSB group (Simms, Keller, Gurrola), as well as with the USGS and CGS (collaborators on the project)
Exemplary Figure Figure 4