Assessing Margin-Wide Rupture Behaviors Along the Cascadia Megathrust With 3-D Dynamic Rupture Simulations

Area of Science:

• Geophysics
• Seismology
• Tectonics

Background:

• The Pacific Northwest coast, from California to British Columbia, is at high risk of major earthquakes and tsunamis originating from the Cascadia subduction zone.
• Evidence indicates that large megathrust earthquakes (magnitude 8+) have occurred historically, with the most recent in 1700 A.D.
• Key uncertainties remain regarding the initiation points, rupture propagation conditions, and slip distribution of future great megathrust events.

Purpose of the Study:

• To develop the first 3-D fully dynamic rupture simulations for the Cascadia subduction zone.
• To investigate the influence of fault stress, strength, and friction on earthquake rupture dynamics.
• To address outstanding questions about nucleation location, rupture extent, and slip magnitude for future great earthquakes.

Main Methods:

• Utilized 3-D fully dynamic rupture simulations driven by fault stress, strength, and friction.
• Constrained initial dynamic stress drop distribution using geodetic coupling models.
• Incorporated segment locations derived from geologic analyses.

Main Results:

• Demonstrated the sensitivity of nucleation location and stress drop to seismic moment and coseismic subsidence.
• Found that final earthquake size is strongly dependent on the slip deficit in central Cascadia, especially for specific initiation locations.
• Developed simulations that can replicate the 1700 A.D. coastal subsidence without requiring localized high-stress asperities.

Conclusions:

• The study provides crucial insights into the mechanics of great earthquakes in the Cascadia subduction zone.
• Results can inform earthquake and tsunami hazard assessments for the Pacific Northwest and other subduction zones with limited seismic data.
• The findings highlight the importance of geodetic coupling models and dynamic rupture simulations in understanding subduction zone earthquake behavior.