SCEC Award Number 16075 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Dynamic and Kinematic Modeling of Backthrust Faulting on the Ventura Fault System: Validation using the San Simeon Earthquake
Name Organization
Percy Galvez AECOM Jeff Bayless AECOM Paul Somerville AECOM
Other Participants
SCEC Priorities 4a, 4e, 6b SCEC Groups CCSP, GMP, FARM
Report Due Date 03/15/2017 Date Report Submitted 03/15/2017
Project Abstract
We use dynamic rupture modeling to investigate the conditions under which conjugate backthrust fault-ing can occur, and to use kinematic ground motion simulations, guided by the dynamic modeling, in broadband simulations of conjugate backthrust faulting. Special focus is placed on the Ventura fault system, which is the subject of a special fault study area. We use SPECFEM3D (Galvez et. al., 2014, 2016) to perform dynamic rupture modeling for branching faults. The rupture process is simulated by rate-and-state friction with aging law. To compute the initial parameters, we perform earthquake cycle modeling. We use a quasi-dynamic solver with adaptive time step to resolve the interseismic period and naturally nucleate the earthquake. Once the event nucleates, we import the stresses, friction and state to the dynamic solver to perform dynamic rupture modeling. In this way, we do not need to prescribe or guess the initial conditions needed for the dynamic modeling. Once the rupture nucleates on the deep section of the Ventura fault, the rupture propagates up-dip and reaches the junction with the Lion backthrust fault in about 5 seconds. At the junction, the rupture splays and breaks the Lion backthrust and dies out after a few seconds, breaking only the deep section of the Lion fault. The second rupture on the Ventura fault continues and breaks the free surface. We use the rupture time, slip functions, and final slip from the dynamic rupture simulations o perform kinematic rupture modeling of the ground motions from splay ruptures.
Intellectual Merit Ground motion prediction equations are based on a single fault plane representation of the earthquake source, and therefore do not provide reliable estimates of ground motions from complex fault systems such as conjugate backthrust faults. Kinematic ground motion simulation can be used to estimate the ground motions from such complex faults, but there are many uncertainties in the details of how the main and backthrust fault segments interact which can only be addressed using dynamic rupture modeling. We need to understand how rupture initiates on the backthrust fault, so that we can kinematically model its location and timing. In the modeling of individual fault segments, we need to know which source parameters such as rise time, slip duration and final slip should be determined from the seismic moment of the backthrust segment rather than those of the overall event.
Broader Impacts This project has supported the already strong collaboration of the group of scientists who work on and for the SCEC broadband platform, by contributing to the research goals and interacting on a regular basis with scientists (and engineers.) Possible benefits of the activity to society involve the improvement of earthquake simulations, which will eventually be used in seismic design, particularly for near fault ground motions.
Exemplary Figure Figure 4. The snapshot sequence of the splay rupture for Ventura-Lion faults. This earthquake nucleates on the ramp of the Ventura fault.