SCEC Award Number 17162 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title A multi-surface plasticity model for 3D wave propagation simulation using AWP
Investigator(s)
Name Organization
Daniel Roten San Diego State University Kim Olsen San Diego State University Yifeng Cui University of California, San Diego
Other Participants
SCEC Priorities 4a, 4c, 2c SCEC Groups CS, Seismology, GM
Report Due Date 06/15/2018 Date Report Submitted 11/12/2018
Project Abstract
 We have implemented an Iwan-type plasticity model in the CPU version of the AWP finite difference (FD) code. AWP-Iwan tracks a series of von Mises yield surfaces arranged in a parallel-series configuration, which in combination reproduce Masing unloading and reloading behavior in three dimensions. The implementation was verified against the 1D FD difference code Noah by simulating the site response of the KiK-net site KSRH10. A verification run for a 2D sediment-filled valley was also carried out, using solutions obtained with Noah2D as a reference. Synthetics obtained with AWP-Iwan using 20 yield surfaces were found to be consistent with the reference solutions in the time and frequency domains. AWP-Iwan was deployed on NCSA Blue Waters to simulate a M 7.8 earthquake on the southern San Andreas fault with realistic near-surface nonlinear behavior in the fill of sedimentary basins. These simulations confirm the importance of nonlinear effects on long-period surface waves during a ShakeOut-type earthquake scenario, with spectral accelerations at 3s reduced by ∼50% in Whittier Narrows and downtown Los Angeles with respect to a linear simulation.
Intellectual Merit This project directly addressed one of SCEC's basic question of earthquake science (Q4). Effects of nonlinearity in surface waves have not received enough attention in the past, yet they are fundamental to the question of whether
the classic separate treatment of source, path and site effects is appropriate. Results of our simulations, carried out using a realistic multi-surface plasticity model, confirm that nonlinear effects in surface waves would be important during a M7.8 earthquake on the southern San Andreas fault. The improved code will be useful for ground motion prediction in many other scenarios. Lessons learned from the implementation of the Iwan model in AWP could prove valuable for developers of other finite difference and finite element codes, especially in the framework of the very successful collaboration within the SCEC/USGS rupture code verification and validation project.
Broader Impacts SCEC activities such as the Shakeout drill and Cybershake continue to have a broad impact on earthquake preparedness and resilience. This research will improve the accuracy of future earthquake scenario simulations (such as ShakeOut) by accounting for realistic nonlinear soil behavior. Current research aims to account for nonlinear effects explored in our simulations into Cybershake, and pave the wave for physics-based seismic hazard maps at frequencies beyond 1 Hz.
Exemplary Figure Figure 10: Minimum value of shear modulus G, normalized by low-strain shear modulus Gmax, at the free
surface encountered during the simulation.