SCEC Award Number 13163 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 (UCR)
SCEC Priorities 6, 4, 3 SCEC Groups FARM, GMP
Report Due Date 03/15/2014 Date Report Submitted N/A
Project Abstract
 The Ventura Basin in Southern California is an area that is increasingly recognized to present a significant seismic hazard. It is underlain by a network of dip-slip faults that appear to connect at depth, raising the possibility that they may rupture in a large multisegment earthquake with magnitude up to 7.6 (Hubbard, 2011). In addition, at least two large thrust faults (the Ventura/Pitas Point and Red Mountain) extend offshore, and may thus produce a significant local tsunami whether they rupture separately or in tandem. We are working on 3D dynamic rupture models for potential earthquakes in the Ventura Basin and offshore, and plan to use the ground motion output from these models to produce scenario tsunami models. This work is part of a coordinated approach to examine the hazard associated with the Ventura Anticline and Thrust System SFSA. In the past year we have been working on integrating our finite element code with meshing software that will allow us to model the full geometrical complexity of this fault system. We have made good progress in this respect, and plan to begin our numerical modeling within the next few months. In this annual report, we present our current meshes for the fault system, which point the way toward our next steps. The results will advance the science of tsunami research by including dynamic modeling as its foundation, and will have important implications for both seismic and tsunami hazard in the Ventura area.
Intellectual Merit This work is still very much in progress, so we do not have any specific research results to report at this time. However, we have done quite a bit of work in incorporating accurate fault geometry for the Ventura Basin fault system into our finite element numerical modeling method. We are currently integrating the meshing software CUBIT with the finite element code FaultMod (Barall, 2009) to allow us to model the fault geometry of this system in great detail. Proper incorporation of fault geometry will be crucial in our quest to determine the rupture extent of likely earthquakes in the region, and in particular whether earthquakes may propagate between different faults, generating much larger magnitude events than had previously been thought possible.

We use fault geometry based on that of Hubbard (2011).These faults may be meshed using triangular or quadrilateral faces, and then the bulk is meshed with either tetrahedra or hexahedra. Our next step, which we hope to begin in a month or two, is to run preliminary spontaneous dynamic rupture models on the Pitas Point fault, and use the results to produce a simple set of tsunami scenarios for this follow. This work will help to advance SCEC’s goal to study the Ventura Basin Special Fault Study Area (SFSA) in terms of its earthquake and tsunami hazard potential. As new faulting data become available, we will incorporate it into our models. With the development of this flexible combination of meshing and dynamic modeling, we will be able to produce realistic models that we hope will be useful to the broader community.
Broader Impacts Our results 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.
Exemplary Figure Figure 2. Meshed faults in the Ventura Basin as visualized in CUBIT. Fault geometry from Hubbard (2011). The faults are meshed at low resolution for ease of visualization; actual fault mesh will be much higher resolution.