Partial ruptures governed by the complex interplay between geodetic slip deficit, rigidity, and pore fluid pressure in 3D Cascadia dynamic rupture simulations

Physics-based simulations are crucial to assessing the seismic hazard in the Cascadia subduction zone (CSZ), requiring assumptions about fault stress and material properties. Geodetic slip deficit models (SDMs) may inform the initial stresses governing megathrust earthquake dynamics. We present a unified workflow linking SDMs to 3D dynamic rupture simulations, and 22 rupture scenarios to unravel the dynamic trade-offs of assumptions on SDMs, rigidity, and pore fluid pressure. We find that margin-wide rupture requires a large slip deficit in the central CSZ. Comparisons between Gaussian and smoother, shallow coupled SDMs show significant differences in stress distributions and rupture dynamics. Variations in depth dependent rigidity cause competing effects, particularly in the near-trench region. Higher overall rigidity can increase fault slip but also result in lower initial shear stresses, inhibiting slip. The state of pore fluid pressure is crucial in balancing the SDM-informed initial shear stresses with realistic dynamic rupture processes, especially assuming small recurrence time scaling factors. This study highlights the importance of self-consistent assumptions on rigidity and initial stresses between geodetic, structural, and dynamic rupture models, providing a foundation for future simulations focusing on ground motions and tsunami generation.