Effects of loading schemes in volumetric simulations of sequences of earthquakes and aseismic slip (SEAS) in subduction zones

Jeena Yun , Yuri Fialko , Dave A May, Alice-Agnes Gabriel, Charles A Williams, Dunyu Liu 

State-of-the-art simulations of sequences of earthquakes and aseismic slip (SEAS) require realistic loading conditions and physics-based constitutive laws to produce the full spectrum of fault slip. Previous studies have shown that loading schemes may affect long-term system behavior, including earthquake recurrence intervals. However, the effects of loading schemes on rupture characteristics and off-fault deformation patterns remain poorly understood, particularly for non-planar dipping faults. Here, we systematically compare three loading schemes for a curved megathrust. In "parallel loading", we prescribe far-field velocities on the sides of a parallelogram-shaped domain aligned with the deep fault root. In "side push loading", we prescribe horizontal shortening. In "subducting slab loading", we prescribe a constant velocity at the bottom of the subducting plate. We find that earthquake sequences are similar under parallel and side push loading schemes, whereas additional complexity emerges under subducting slab loading, exhibiting different recurrence intervals, average slip, and stress drops. Parallel and side push loading schemes result in a long-term accumulation of vertical displacements and fault-normal stresses, which is mitigated under subducting slab loading. Among the three loading methods, subducting slab loading scheme produces deformation patterns most consistent with geodetic observations, including surface displacements due to earthquakes, afterslip, and slow slip events. We further examine the effects of domain length, slab thickness, and material heterogeneities on simulated rupture characteristics and deformation patterns. These results highlight the role of loading conditions on modeled deformation patterns in SEAS simulations.