Community‐Driven Code Comparisons for Three‐Dimensional Dynamic Modeling of Sequences of Earthquakes and Aseismic Slip

Abstract

Dynamic modeling of sequences of earthquakes and aseismic slip (SEAS) provides a self‐consistent, physics‐based framework to connect, interpret, and predict diverse geophysical observations across spatial and temporal scales. Amid growing applications of SEAS models, numerical code verification is essential to ensure reliable simulation results but is often infeasible due to the lack of analytical solutions. Here, we develop two benchmarks for three‐dimensional (3D) SEAS problems to compare and verify numerical codes based on boundary‐element, finite‐element, and finite‐difference methods, in a community initiative. Our benchmarks consider a planar vertical strike‐slip fault obeying a rate‐ and state‐dependent friction law, in a 3D homogeneous, linear elastic whole‐space or half‐space, where spontaneous earthquakes and slow slip arise due to tectonic‐like loading. We use a suite of quasi‐dynamic simulations from 10 modeling groups to assess the agreement during all phases of multiple seismic cycles. We find excellent quantitative agreement among simulated outputs for sufficiently large model domains and small grid spacings. However, discrepancies in rupture fronts of the initial event are influenced by the free surface and various computational factors. The recurrence intervals and nucleation phase of later earthquakes are particularly sensitive to numerical resolution and domain‐size‐dependent loading. Despite such variability, key properties of individual earthquakes, including rupture style, duration, total slip, peak slip rate, and stress drop, are comparable among even marginally resolved simulations. Our benchmark efforts offer a community‐based example to improve numerical simulations and reveal sensitivities of model observables, which are important for advancing SEAS models to better understand earthquake system dynamics.

Characteristics of Earthquake Cycles: A Cross‐Dimensional Comparison of 0D to 3D Numerical Models

“…Therefore both the interseismic and coseismic characteristics are not sensitive to what kind of loading boundary condition is applied. Comparison in the SEAS benchmark BP4‐QD of different modeling groups demonstrated the same idea: numerical results generally agreed with each other when computational domain was large enough, where for the numerical method's convenience, either stress‐free or constant‐moving boundary condition is chosen at far‐away boundaries (Jiang et al., 2022).…”

Rate and State Friction as a Spatially Regularized Transient Viscous Flow Law

“…We have also seen that the diffusion process is associated with a smaller time scale, and thus, stricter time step constraints than the interfacial model. We note that both spatial and temporal resolution requirements already place challenging constraints on simulations of seismic and aseismic slip sequences (Erickson et al, 2020;Jiang et al, 2022).…”

Contribution of Viscoelastic Stress to the Synchronization of Earthquake Cycles on Oceanic Transform Faults

“…During rupture propagation, the smallest size of the system is a stress concentration near the rupture tip. Numerical models of the seismic cycle with rupture propagation need to resolve the length scale of the cohesion zone, estimated as (Day et al, 2005;Jiang et al, 2022;Lapusta & Liu, 2009)…”