Towards bridging the SEAS and earthquake simulator efforts: Using the Cajon Pass earthquake gate as a test site

Benchun Duan, Qingjun Meng, & Zhi Shang

Published September 10, 2023, SCEC Contribution #12976, 2023 SCEC Annual Meeting Poster #122

The SEAS group in SCEC has been working on verifying various codes in the community for simulating the Sequences of Earthquakes and Aseismic Slip (SEAS) in recent years. Another group working on earthquake simulators (such as RSQSim) has a longer history. These classical earthquake simulators do not simulate the spontaneously dynamic rupture process, though they can be applied to complex fault systems such as the San Andreas Fault system (SAF). The codes in the SEAS group have the potential to include spontaneous rupture simulation, but most simulations done by these codes have been limited to simple fault geometry. We have been developing a finite-element-method (FEM) code to simulate earthquake cycles with spontaneous rupture included, which can be applied to geometrically complex faults. We call this type of codes as dynamic earthquake simulators, which can bridge the SEAS and earthquake simulator efforts.

Our dynamic earthquake simulator is based on an explicit FEM code EQdyna, which is one of the codes in the SCEC dynamic rupture code verification group. EQdyna is directly used to simulate the dynamic rupture process, while a dynamic relaxation technique is adopted to allow EQdyna to simulate the quasi-static processes of earthquake cycles, including the nucleation, postseismic and interseismic processes. This EQdyna-based dynamic earthquake simulator has been applied to study seismic and aseismic slip behavior on a shallow dipping subduction zone. To apply it to geometrically complex fault systems such as SAF, we need to integrate it with a third-party meshing code that can generate high-quality hexahedral elements for complex fault geometry, as EQdyna primarily uses hexahedral elements for computing efficiency. This also involves how to partition a large, geometrically complex model domain into smaller domains for MPI-based high-performance computing. In this study, we address these issues with the Cajon Pass earthquake gate as a test site. We choose Coreform Cubit as the meshing code, and we use Metis and Scotch for mesh domain partitioning. We develop a workflow for the test site, including extracting the fault geometry from SCEC CFM, converting it into STL format, meshing in Cubit, partitioning by Metis and Scotch, and integrating with EQdyna. We apply this workflow to the test site for a dynamic rupture simulation. We will continue this effort to explore rupture behaviors of the Cajon Pass over many earthquake cycles in the future.

Citation
Duan, B., Meng, Q., & Shang, Z. (2023, 09). Towards bridging the SEAS and earthquake simulator efforts: Using the Cajon Pass earthquake gate as a test site. Poster Presentation at 2023 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)