SCEC Award Number 12208 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Quasi-Dynamic Earthquake Cycle Simulations with Off-Fault Plasticity
Investigator(s)
Name Organization
Eric Dunham Stanford University
Other Participants Brittany Erickson (postdoc, Stanford)
SCEC Priorities 3f, 3c, 2e SCEC Groups FARM, SDOT, GMP
Report Due Date 03/15/2013 Date Report Submitted N/A
Project Abstract
 We have developed a numerical method for simulating full earthquake cycles with multiple events with rate-and-state friction, variable material properties and off-fault plasticity. The volume discretization present in our model allows us to incorporate these features, where we use finite dierences and weak enforcement of boundary conditions. We assume antiplane deformation in 2d and solve the equations for static equilibrium. Our adaptive time-stepping method allows us to integrate quickly through the interseismic period as well as fully resolve quasi-dynamic rupture. We used this method to study how both material heterogeneities and off-fault plasticity aect the earthquake process. We queried the SCEC-CVM database in order to account for material properties at depth at various locations in southern California. We found the presence of a sedimentary basin increases the recurrence interval for earthquakes, as well as introduces the emergence of a sub-basin rupture preceding each event. In order to account for o-fault plasticity, we further developed our method to solve an incremental problem where the constitutive relation involves an elastoplastic tangent stiffness tensor. Thus far we have been able to simulate multiple earthquakes which cause plastic yielding to occur and plastic strain to accrue. This will be useful in further studies to understand how damage left by past earthquakes aects subsequent events.
Intellectual Merit Earthquake cycle modeling will soon become an integral part of earthquake forecasting, as it permits us to study interactions between multiple events and even different faults. In the context of this long-term objective, our present research has focused on developing numerical methods for earthquake modeling with rate-and-state friction, spatially variable material properties, and off-fault inelastic deformation. All are likely to be fundamental to the physics of earthquake nucleation, propagation, arrest, and interaction.
Broader Impacts The project supported the training of postdoctoral fellow Brittany Erickson. The research will eventually lead to more realistic physics-based earthquake cycle modeling capabilities that can be employed to characterize earthquake interactions and the long-term tectonic behavior of faults in sedimentary basins and other structurally complex areas.
Exemplary Figure Figure 2: (a) Blue is surface slip velocity with no basin (recurrence interval is slightly less than 150 years). Basin with a depth of 4 km (red), the recurrence interval increases to approximately 200 years. Basin simulation experiences a sub-basin rupture, which is felt at surface around 100 years after each event. Basin yields larger values for the max surface slip velocity. (b) Slip profiles plotted in solid black contours every 5 years during the interseismic period (when max(V ) < 1 mm/s) and in dashed every second during quasidynamic event. A sub-basin event emerges, unable to penetrate through the basin, followed by full-basin rupture that reaches the surface. Slip is inhibited by the presence of the basin. The sub-basin rupture leaves a stress concentration, which allows the next event to propagate all the way to the surface.
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