Arthur Rodgers | 19-ERD-037
Physics-based, three-dimensional (3D) numerical simulations of earthquake ground motions provide an alternative to reliance on limited and highly scattered empirical data and models for seismic hazard assessment. In this project, we demonstrated that high resolution, fully deterministic earthquake ground motions can be calculated to higher frequencies than have ever been considered. We performed fully 3D earthquake ground motion simulations on the Sierra and Lassen high-performance computing (HPC) platforms at Lawrence Livermore National Laboratory. Ground motions were computed with SW4, a summation-by-parts finite difference code for anelastic wave propagation. The Laboratory's HPC platforms feature graphics processing unit (GPU) acceleration for improved performance, and SW4 was recently enhanced to run efficiently on GPU-accelerated platforms.
We found that SW4 runs almost fifty times faster in terms of node-hours on new GPU-accelerated platforms compared to conventional central processing unit (CPU) platforms with agreement of computed ground motion time-series to the full single precision which they are written. On Sierra, focusing on moment magnitude (M W ) 7.0 earthquakes on the Hayward Fault, we ran three simulations resolving ground motions from static displacements (0 Hz) to frequencies of 10 Hz (wavelengths as short as 50 meters) making the highest resolution, regional scale earthquake simulations for California. Results showed good agreement between simulated ground motion intensities (peak ground velocity and acceleration, spectral response) and empirical models, including frequencies above 10 Hz. On Lassen, we ran a suite of 52 M W 7.0 Hayward Fault earthquake simulations resolved 0-5 Hz for both plane-layered one-dimensional (1D) and 3D Earth models. The simulations were used to develop a methodology for characterizing and removing systematic path and site effects that bias ground motion intensities. Simulations using the newly enhanced SW4 code enable us to run higher resolution seismic simulations with shorter run times, providing a new capability for seismic hazard and risk studies.
Impact on Mission
Our research leveraged the Laboratory's core capabilities in HPC, simulation, and data science–including the Sierra and Lassen GPU-accelerated platforms–along with Livermore's advanced numerical methods for wave propagation to provide a new approach for more efficient seismic simulations. This work benefits safety, energy, and national security programs of importance to the nation, the Laboratory, and research partners from academia and the energy industry.
Publications, Presentations, Etc.
Rodgers, A., et al. 2018. "Sierra Advances Resolution of Hayward Fault Earthquake Simulations." Technical Report, Lawrence Livermore National Laboratory, Livermore, CA. doi: 10.2172/1476179. LLNL-TR-758317.
Rodgers, A. 2019. "Pushing the Limits of Regional-Scale Fully Deterministic Large Earthquake Ground Motion Simulations on High-Performance Computers with Three-Dimensional Earth Structure and Topography: Hayward Fault Scenarios and Generic Ruptures in Simple Models." Presentation at the Seismological Society of America Annual Meeting, Seattle, WA, April 2019. LLNL-PRES-772604.