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Published March 1, 2020 | Submitted
Journal Article Open

Community Code Verification Exercise for Simulating Sequences of Earthquakes and Aseismic Slip (SEAS)


Numerical simulations of sequences of earthquakes and aseismic slip (SEAS) have made great progress over past decades to address important questions in earthquake physics. However, significant challenges in SEAS modeling remain in resolving multiscale interactions between earthquake nucleation, dynamic rupture, and aseismic slip, and understanding physical factors controlling observables such as seismicity and ground deformation. The increasing complexity of SEAS modeling calls for extensive efforts to verify codes and advance these simulations with rigor, reproducibility, and broadened impact. In 2018, we initiated a community code‐verification exercise for SEAS simulations, supported by the Southern California Earthquake Center. Here, we report the findings from our first two benchmark problems (BP1 and BP2), designed to verify different computational methods in solving a mathematically well‐defined, basic faulting problem. We consider a 2D antiplane problem, with a 1D planar vertical strike‐slip fault obeying rate‐and‐state friction, embedded in a 2D homogeneous, linear elastic half‐space. Sequences of quasi‐dynamic earthquakes with periodic occurrences (BP1) or bimodal sizes (BP2) and their interactions with aseismic slip are simulated. The comparison of results from 11 groups using different numerical methods show excellent agreements in long‐term and coseismic fault behavior. In BP1, we found that truncated domain boundaries influence interseismic stressing, earthquake recurrence, and coseismic rupture, and that model agreement is only achieved with sufficiently large domain sizes. In BP2, we found that complexity of fault behavior depends on how well physical length scales related to spontaneous nucleation and rupture propagation are resolved. Poor numerical resolution can result in artificial complexity, impacting simulation results that are of potential interest for characterizing seismic hazard such as earthquake size distributions, moment release, and recurrence times. These results inform the development of more advanced SEAS models, contributing to our further understanding of earthquake system dynamics.

Additional Information

© 2020 Seismological Society of America. Manuscript received 5 September 2019; Published online 29 January 2020. The authors thank Steve Day, Alice‐Agnes Gabriel, Jeff McGuire, and Fred Pollitz for reviewing the article. Brittany A. Erickson, Junle Jiang, and Michael Barall were supported through the Southern California Earthquake Center Grant Numbers 18099 and 19109. Two sequences of earthquakes and aseismic slip (SEAS)‐themed workshops were funded by Southern California Earthquake Center (SCEC) Award Numbers 17151 and 18102. SCEC is funded by National Science Foundation (NSF) Cooperative Agreement EAR‐0529922 and U.S. Geological Survey (USGS) Cooperative Agreement 07HQAG0008. This is SCEC Contribution Number 9066. Brittany A. Erickson and Junle Jiang designed the benchmark problems, analyzed model results, co‐organized the workshops and cowrote this article, with equal contributions. Michael Barall developed and maintains the online platform. Michael Barall, Nadia Lapusta, Eric M. Dunham, and Ruth Harris provided major support and advice in forming the working group, obtaining funding, and manuscript writing. Remaining coauthors provided feedback on benchmark designs, participated in the benchmark exercises, helped revise the article and are hence listed alphabetically. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Data and Resources: Our online platform (http://scecdata.usc.edu/cvws/seas/) is being developed and maintained by Michael Barall. The data for local fault properties are stored on the platform. Full details of the benchmark including governing equations and initial and fault interface conditions are available at http://scecdata.usc.edu/cvws/seas/index.html. Southern California Earthquake Center (SCEC) funded workshop presentations are available at http://scecdata.usc.edu/cvws/seas/workshop_presentations.html. SCycle code is available at https://github.com/kali-allison/SCycle. FDCycle code is available at https://github.com/brittany-erickson/FDCycle. QDESDG code is available at https://github.com/jkozdon/QDESDG. Quasi‐DYNamic earthquake simulator (QDYN) code is available at https://github.com/ydluo/qdyn. All websites were last accessed in December 2019.

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