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Physics-based dynamic rupture simulations are valuable for assessing the seismic hazard in the Cascadia subduction zone (CSZ), but require assumptions about fault stress and material properties. Geodetic slip deficit models (SDMs) may provide information about 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 for SDMs, rigidity, and pore fluid pressure. We find that margin-wide rupture, an earthquake that ruptures the entire length of the plate boundary, 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 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 for rigidity and initial stresses between geodetic, structural, and dynamic rupture models, providing a foundation for future simulations of ground motions and tsunami generation.
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The State of Pore Fluid Pressure and 3‐D Megathrust Earthquake Dynamics
Abstract We study the effects of pore fluid pressure (Pf) on the pre‐earthquake, near‐fault stress state, and 3‐D earthquake rupture dynamics through six scenarios utilizing a structural model based on the 2004Mw9.1 Sumatra‐Andaman earthquake. As pre‐earthquakePfmagnitude increases, effective normal stress and fault shear strength decrease. As a result, magnitude, slip, peak slip rate, stress drop, and rupture velocity of the scenario earthquakes decrease. Comparison of results with observations of the 2004 earthquake support that pre‐earthquakePfaverages near 97% of lithostatic pressure, leading to pre‐earthquake average shear and effective normal tractions of 4–5 and 22 MPa. The megathrust in these scenarios is weak, in terms of low mean shear traction at static failure and low dynamic friction coefficient during rupture. Apparent co‐seismic principal stress rotations and absolute post‐seismic stresses in these scenarios are consistent with the variety of observed aftershock focal mechanisms. In all scenarios, the mean apparent stress rotations are larger above than below the megathrust. Scenarios with largerPfmagnitudes exhibit lower mean apparent principal stress rotations. We further evaluate pre‐earthquakePfdepth distribution. IfPffollows a sublithostatic gradient, pre‐earthquake effective normal stress increases with depth. IfPffollows the lithostatic gradient exactly, then this normal stress is constant, shifting peak slip and peak slip rate updip. This renders constraints on near‐trench strength and constitutive behavior crucial for mitigating hazard. These scenarios provide opportunity for future calibration with site‐specific measurements to constrain dynamically plausible megathrust strength andPfgradients.
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- Award ID(s):
- 2121568
- PAR ID:
- 10369466
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Solid Earth
- Volume:
- 127
- Issue:
- 4
- ISSN:
- 2169-9313
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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