SCEC Award Number 17184 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Testing fault geometry and interaction models using high-precision slip rates on the San Cayetano and Ventura-Pitas Point Faults
Investigator(s)
Name Organization
Dylan Rood University of California, Santa Barbara
Other Participants Tom Rockwell (San Diego State University), Duane DeVecchio (Arizona State University), Craig Nicholson (UC Santa Barbara), Scott Marshall (Appalachian State University), UCSB graduate student (1)
SCEC Priorities 1a, 3a, 5b SCEC Groups Geology, CXM, SDOT
Report Due Date 06/15/2018 Date Report Submitted 11/15/2018
Project Abstract
 We investigated surface evidence and displacement rates for the Southern San Cayetano fault (SSCF). Active faulting displaces young landforms, such as late Quaternary river terraces and alluvial fans. Geomorphic strain markers were examined using field mapping, high-resolution lidar topographic data, 10Be surface exposure dating, and subsurface well data to provide evidence for a young, active SSCF along the northern flank of the Santa Clara River Valley.
We conducted geomorphic mapping to identify alluvial terraces and fans deformed by the SSCF. We collected samples from this suite of surfaces to measure in-situ-produced cosmogenic 10Be surface exposure ages using depth profiles. Ages for the surfaces range from 7.3 +1.8/-1.7 ka to 58.4 +12.7/9.0 ka. Maximum slip rates for the central SSCF are 1.9 +1.0/-0.5 mm yr-1 between ~19–7 ka and minimum slip rates are 1.3 +0.5/-0.3 mm yr-1 since ~7 ka. Uplift rates for the central SSCF have not varied significantly over the last ~58 ka, with a maximum value of 1.7 +0.9/-0.6 mm yr-1 for the interval ~58–19 ka, and a minimum value 1.2 +/- 0.3 mm yr-1 since ~7 ka. The SSCF is interpreted as a young, active structure with onset of activity at some point after ~58 ka.
Based on our results, we suggest that the SSCF may rupture in tandem with the main San Cayetano fault. Additionally, the SSCF could potentially act as a rupture pathway between the Ventura and San Cayetano faults in large-magnitude, multi-fault earthquakes in southern California.
Intellectual Merit This project directly addresses the following SCEC5 Basic Questions of Earthquake Science: Question 1 (Q1) by refining slip-rates on a recently identified structure within the southern California fault system (Priority 1.a), Q3 by refining the geometry of active faults (P3.a), and Q5 by providing geologic constraints on large multi-fault ruptures (P5.b). Our work has also contributed to the Earthquake Geology Disciplinary Committee by 1) assisting in the quantification of along-strike variations in strain localization, specifically as it applies to multi-fault ruptures on major reverse faults in the WTR and 2) utilizing the Geochronology Infrastructure. It also directly contributes to the following Interdisciplinary Working Groups: Stress and Deformation Over Time (SDOT) and SCEC Community Models (SCM) by providing information on geologic fault slip rates and subsurface fault geometry that can be used to evaluate 1) deformation and earthquake cycle models and 2) the Community Fault Model (CFM), respectively. It has importance to the USGS EHP programs (i.e. National Seismic Hazard Mapping Program) and WGCEP. Our work provides a “proof of concept” dataset that can be used as leverage to pursue additional funding from other sources, including NSF and USGS NEHRP.
Broader Impacts This work supported one Masters student project and was conducted by PI Rood in conjunction with a PhD student as part of a wider PhD project investigating the tectonic geomorphology and seismic hazards of the Ventura Basin. The work provided one Masters student and two PhD students with valuable experience in earthquake geology field work, and enabled one Masters student and one PhD student to learn the theory, laboratory procedures, and application of cosmogenic isotopes in Earth Sciences. The work resulted in the following publication:
A. Hughes, D.H. Rood, A.C. Whittaker, R.E. Bell, T.K. Rockwell, Y. Levy, K.M. Wilcken, L.B. Corbett, P.R. Bierman, D.E. DeVecchio, S.T. Marshall, L.D. Gurrola, C. Nicholson, Geomorphic evidence for the geometry and slip rate of a young, low-angle thrust fault: Implications for hazard assessment and fault interaction in complex tectonic environments, Earth and Planetary Science Letters, Volume 504, 2018, Pages 198-210, ISSN 0012-821X, https://doi.org/10.1016/j.epsl.2018.10.003.
Exemplary Figure Figure 6