SCEC Award Number 07146 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Study of the bimaterial effect and potential preferred rupture direction through simulations of earthquake sequences
Investigator(s)
Name Organization
Nadia Lapusta California Institute of Technology
Other Participants Yi Liu, graduate student
SCEC Priorities A9, A8, A7 SCEC Groups FARM, EFP
Report Due Date N/A Date Report Submitted N/A
Project Abstract
 In this project, the goal was to study the dynamics of bimaterial faults, e.g., faults between two dissimilar elastic media. The initial plan was to extend the spectral boundary element formulation - that had been successfully used to study earthquake sequences in models with the uniform elastic bulk - to the bimaterial models. Unfortunately, variable time stepping that works very well for the case of the same material on both sides of the fault does not lead to stable simulations in the bimaterial case. Hence we have concentrated our efforts on developing a spectral element methodology (SEM) for simulating long-term slip histories. By combining implicit quasi-static SEM with fully dynamic SEM, we were able to simulate a long-term slip history that included aseismic slip punctuated by a sequence of dynamic ruptures in a simple 2D earthquake model of a fault that separates identical elastic media. The results are in excellent agreement with the boundary-integral simulations of the same problem. Since SEM readily allows variations in bulk properties, and since the quasi-static part of the simulation is already fully implicit and hence allows to variable time stepping, extending the code to the bimaterial problem should not pose any conceptual difficulty.
Intellectual Merit The research has led to the development of the modeling approach that allows to study long-term history of the fault – including earthquake sequences – in fault models with heterogeneous bulk, including bimaterial, layered, and damage-zone scenarios. Understanding earthquake behavior in such more realistic models is directly related to the SCEC mission “to develop physics-based models of the nucleation, propagation and arrest of dynamic earthquake ruptures”.
Broader Impacts The project involved two graduate students, who received training in this multidisciplinary project. One of the students was from the engineering background.
Exemplary Figure Figure 2. Comparison of simulation results for the SEM and BIM methods. Several years have been simulated, and the fault produced a sequence of small repeating events. The agreement between the two methods is excellent. The developed SEM methodology can be used for simulating long-term histories of seismic and aseismic slip in the bimaterial problem.
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