Using dynamic earthquake rupture models to quantify rupture characteristics and upper plate deformation for the Cascadia megathrust

T here is ample geologic evidence to support the occurrence of multiple M>8 and larger earthquakes along the Cascadia megathrust for the last ~10 kya. Coseismic subsidence was observed along the Pacific Northwest coastline during the most recent event in 1700 A.D.

However, because there are no modern seismic recordings of megathrust earthquakes for this subduction zone, most rupture simulation efforts to date have focused on how stochastic or kinematic on-fault slip parameterizations borrowed from other megathrust events (e.g., Tohoku, Maule) affect tsunami hazard or predict ground motions. Geodetic observations, on the other hand, are readily available above the Cascadia megathrust and suggest varying degrees of locking, or slip deficit.

We take geodetic inversions for slip-rate deficit and convert them to slip by assuming megathrust recurrence intervals constrained by paleoseismic data. We then go one step further and use these kinematic slip parameterizations to derive initial shear stress levels on the megathrust as initial input into our dynamic rupture simulations. Furthermore, we build upon previously designed 2D dynamic rupture models (Ramos and Huang, 2019) that incorporate an abruptly positive to negative stress drop from the base of the locked to transition regions of the fault.

Our goal is to use physics-based dynamic rupture simulations to elucidate which factors are most important for controlling down-dip or along-strike rupture extent and to investigate how the interplay of topography and fault curvature influences coseismic uplift or subsidence. Understanding the role of geometry, material effects, and heterogeneous fault strength distributions will benefit seismic hazards analysis by providing physically informed earthquake scenarios for the Pacific Northwest.