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ABSTRACT: Numerical modeling of earthquake dynamics and derived insight for seismic hazard relies on credible, reproducible model results. The sequences of earthquakes and aseismic slip (SEAS) 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. Seven and eight modeling groups participated in BP1-FD and BP3-QD, respectively, allowing us to explore these physical ingredients across multiple codes and better understand associated numerical considerations. With new comparison metrics, we find that numerical resolution and computational domain size are critical parameters to obtain matching results. Codes for BP1-FD implement different criteria for switching between quasi-static and dynamic solvers, which require tuning to obtain matching results. In BP3-QD, proper remote boundary conditions consistent with specified rigid body translation are required to obtain matching surface displacements. With these numerical and mathematical issues resolved, we obtain excellent quantitative agreements among codes in earthquake interevent times, event moments, and coseismic slip, with reasonable agreements made in peak slip rates and rupture arrival time. We find that including full inertial effects generates events with larger slip rates and rupture speeds compared to the quasi-dynamic counterpart. For BP3-QD, 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 similar-size characteristic earthquakes, and others exhibiting different-size events. These findings underscore the importance of considering full elastodynamics and nonvertical dip angles in SEAS models, as both influence short- and long-term earthquake behavior and are relevant to seismic hazard.

Geophysical observations suggest that temporal changes in pore fluid pressure correlate with slow slip events (SSEs) at some subduction zones, including the Hikurangi and Cascadia subduction zones. These fluctuations in pore fluid pressure are attributed to fluid migration before and during SSEs, which may modulate SSE occurrence. To examine the effect of pore fluid pressure changes on SSE generation, we develop numerical models in which periodic pore‐pressure perturbations are applied to a stably sliding, rate‐strengthening fault. By varying the physical characteristics of the pore‐pressure perturbations (amplitude, characteristic length and period), we find models that reproduce shallow Hikurangi SSE properties (duration, magnitude, slip, recurrence) and SSE moments and durations from different subduction zones. The stress drops of modeled SSEs range from ∼20–120 kPa while the amplitudes of pore‐pressure perturbations are several MPa, broadly consistent with those inferred from observations. Our results indicate that large permeability values of ∼10−14 to 10−10 m2 are needed to reproduce the observed SSE properties. Such high values could be due to transient and localized increases in fault zone permeability in the shear zone where SSEs occur. Our results suggest that SSEs may arise on faults in rate‐strengthening frictional conditions subject to pore‐pressure perturbations. Plain Language Summary: Slow slip events (SSEs), with slower velocities and longer durations than regular earthquakes, have been detected at several subduction zones worldwide. Recent observations have led researchers to infer that pore fluid pressure—the pressure of fluids in the pore space of rocks—changes during SSEs that occur along the shallow (<15 km depth) portion of the Hikurangi subduction zone, where the Pacific Plate subducts beneath the Australian plate. Similar observations have been reported during SSEs in different subduction zones. However, how pore fluid pressure changes are linked to SSEs is poorly understood. To investigate this issue, we develop physics‐based models in which periodic perturbations in pore fluid pressure are imposed on a fault governed by the expected frictional behavior of rocks derived from laboratory experiments. These pore fluid pressure perturbations induce SSEs, and the features of these events (duration, magnitude, peak velocity, recurrence interval) change with the characteristics of the pore fluid pressure change (size, amplitude, and period). After exploring different perturbation characteristics, we find models that capture the observed features of SSEs along the Hikurangi margin and in different subduction zones. This study suggests that pore fluid pressure changes may play an important role in SSE occurrence. Key Points: Periodic pore fluid pressure perturbations on a rate‐strengthening fault induce slow slip events (SSEs)Source properties of induced SSEs vary with perturbation characteristics (length scale, amplitude, period)Model reproduces source properties of shallow Hikurangi SSEs, and duration and magnitude of SSEs in different subduction zones [ABSTRACT FROM AUTHOR]