Incorporating Full Elastodynamic Effects and Dipping Fault Geometries in Community Code Verification Exercises for Simulations of Earthquake Sequences and Aseismic Slip (SEAS)

Brittany A. Erickson, Junle Jiang, Valere R. Lambert, Mohamed Abdelmeguid, Martin Almquist, Jean-Paul Ampuero, Ryosuke Ando, Sylvain D. Barbot, Camilla Cattania, Alexandre Chen, Luca Dal Zilio, Eric M. Dunham, Ahmed E. Elbanna, Alice-Agnes Gabriel, Tobias W. Harvey, Yihe Huang, Yoshihiro Kaneko, Jeremy E. Kozdon, Nadia Lapusta, Duo Li, Meng Li, Chao Liang, Yajing Liu, So Ozawa, Casper Pranger, Paul Segall, Yudong Sun, Prithvi Thakur, Carsten Uphoff, Ylona van Dinther, & Yuyun Yang

Under Review September 30, 2022, SCEC Contribution #12627

Numerical modeling of earthquake dynamics and derived insight for seismic hazard relies on credible, reproducible model results. The SEAS (Sequences of Earthquakes and Aseismic Slip) initiative has set out to facilitate community code comparisons, and verify and advance the next generation of physics-based earthquake models that reproduce all phases of the seismic cycle. With the goal of advancing SEAS models to robustly incorporate physical and geometrical complexities, here we present code comparison results from two new benchmark problems: BP1-FD considers full elastodynamic effects and BP3-QD considers dipping fault geometries. Eight modeling groups participated in each benchmark, allowing us to explore these physical ingredients across multiple codes and better understand associated numerical considerations. We find that numerical resolution and computational domain size are critical parameters to obtain matching results, with increasing domain-size requirements posing challenges for volume-based codes even in 2D settings. Codes for BP1-FD implemented different criteria for switching between quasi-static and dynamic solvers, which require tuning to obtain matching results. In BP3-QD, proper remote boundaries conditions consistent with specified rigid body translation are required to obtain matching surface displacements. With these numerical and mathematical issues resolved, we obtain good agreement among codes in long-term fault behavior, earthquake recurrence intervals, and rupture features of peak slip rates and stress drops for both benchmarks. Including full inertial effects generates events with larger slip rates and rupture speeds compared to the quasi-dynamic counterpart. For BP3QD, both dip angle and sense of motion (thrust versus normal faulting) alter ground motion on the hanging and foot walls, and influence event patterns, with some sequences exhibiting similarsized characteristic earthquakes, and others exhibiting several earthquakes of differing magnitudes. These findings underscore the importance of considering full dynamics and non-vertical dip angles in SEAS models, as both influence short and long-term earthquake behavior, and associated hazards.

Key Words
earthquake source processes, wave propagation, aseismic slip, numerical modeling, code verification, community project

Citation
Erickson, B. A., Jiang, J., Lambert, V. R., Abdelmeguid, M., Almquist, M., Ampuero, J., Ando, R., Barbot, S. D., Cattania, C., Chen, A., Dal Zilio, L., Dunham, E. M., Elbanna, A. E., Gabriel, A., Harvey, T. W., Huang, Y., Kaneko, Y., Kozdon, J. E., Lapusta, N., Li, D., Li, M., Liang, C., Liu, Y., Ozawa, S., Pranger, C., Segall, P., Sun, Y., Thakur, P., Uphoff, C., van Dinther, Y., & Yang, Y. (2022). Incorporating Full Elastodynamic Effects and Dipping Fault Geometries in Community Code Verification Exercises for Simulations of Earthquake Sequences and Aseismic Slip (SEAS). Bulletin of the Seismological Society of America, (under review).


Related Projects & Working Groups
SEAS, FRAM, SDOT