SCEC Award Number 14137 View PDF
Proposal Category Individual Proposal (Special Fault Study Area)
Proposal Title Fault Dynamics and Tsunamis in the Ventura Basin
Investigator(s)
Name Organization
David Oglesby University of California, Riverside
Other Participants Kenny Ryan, Ph.D. student, UC Riverside; Eric Geist, Researcher, USGS, Menlo Park
SCEC Priorities 6b, 4a, 3e SCEC Groups USR, FARM, CS
Report Due Date 03/15/2015 Date Report Submitted N/A
Project Abstract
 Abstract: Within the Ventura basin in southern California is a network of coastal dip-slip faults that can likely produce earthquakes of magnitude 7 or greater, as well as significant local tsunamis. We construct a 3D dynamic rupture model of an earthquake on the connected Pitas Point and Lower Red Mountain faults to model low-frequency ground motion and the resulting tsunami, with a goal of elucidating the seismic and tsunami hazard in this area. Our model results in an average static stress drop of 6 megapascals, an average fault slip of 7.6 meters, and a moment magnitude of 7.7, consistent with paleoseismic data in the region. Corresponding tsunami modeling uses the final seafloor displacement from the fault rupture models as initial conditions to compute local propagation and inundation. The tsunami model results in large peak tsunami amplitudes northward and eastward due to site and path effects from bathymetry. In particular, modeled inundation in the Ventura area is significantly greater than that indicated by state of California’s current reference inundation line. Results from these modeling efforts can help indicate regions of high tsunami hazard, and with further development, the use of this methodology in tsunamigenic regions worldwide can contribute to hazard assessments.
Intellectual Merit This proposed work is part of the coordinated effort to investigate the proposed Ventura Anticline and Thrust System SFSA; dynamic rupture modeling and tsunami modeling of the type proposed herein are both cornerstones of this larger project. As such, we are using structural and stressing rate information gathered by other SFSA researchers as soon as they are available. In turn, our source models can be used by other SFSA researchers to help pinpoint the best places for future work to further constrain faulting behavior. Thus, the relationship between modeling and structural determination is a two-way street. This work is related to SCEC Research Objectives 6b (Modeling of ruptures that includes realistic dynamic weakening mechanisms, off-fault plastic deformation, and is constrained by source inversions), 4a (Detailed geologic, seismic, geodetic, and hydrologic investigations of fault complexities at Special Fault Study Areas and other important regions), and 3e (Construction of computational simulations of dynamic earthquake ruptures to help constrain stress levels along major faults, to help explain the heat-flow paradox, and to help us understand extreme slip localization, the dynamics of self-healing ruptures, and the potential for repeated slip on faults during earthquakes).

Broader Impacts This work will have important significance for ground motion and seismic hazard estimates in the Ventura Basin. In particular, the resultant slip models can be used as the basis for broadband ground motion models. The results should also shed light on the likelihood of multi-fault rupture in this region, and thus on the maximum earthquake size. The resultant tsunami models will help to characterize the tsunami hazard in southern California; because they will be based on slip models that are themselves physically based, the tsunami models should provide physically plausible estimates of local runup. In the future, this type of analysis could be applied in multiple locations in California and elsewhere.
This work contributed strongly to the education of a graduate student who is learning both fault dynamic and tsunami modeling.
Exemplary Figure Figure 5. Map of localized peak tsunami amplitude, in meters (around Ventura, CA), resulting from slip on the Pitas Point and Lower Red Mountain fault system. The solid black line indicates the coastline. The solid red line is the statewide tsunami inundation map coordinated by the California Emergency Management Agency. Letters indicate example locations (approximate): SB = Santa Barbara; VH = Ventura Harbor; SCRM = Santa Clara River Mouth; MSB = McGrath State Beach; CIHE = Channel Islands Harbor Entrance. Inset shows the map boundary in black. Note that inundation from the model is significantly greater in many places than the statewide estimate.