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Geodetic Imaging of Strain Partitioning Between the Megathrust and Crustal Faults in Cascadia

Description: 

Strain accumulates in the Cascadia subduction zone region over interseismic periods and is released via large magnitude earthquakes and slow-slip events (SSE). The spatial distribution of strain accumulation can vary due to megathrust geometry, extent of interplate coupling, upper-plate fault configuration, and the degree of forearc segmentation. Here, we use interseismic GNSS surface velocities to constrain elastic block models and evaluate a suite of possible block configurations that are primarily based on the Cascadia Region Earthquake Science Center Community Fault Model. In addition, we include several sets of offshore faults that trend sub-perpendicular to the trench and a network of dip- and strike-slip faults in southern Cascadia to test possible segmentation of the forearc. Because several models fit the inverted GNSS velocities equally well, we compare modeled fault slip rates to geologic estimates and uplift rates to leveling and tidal gauge data in order to delineate between models. Segmented forearc models fit independent uplift rates better than continuous forearc models, and in some cases, the addition of segments improves the model fit of crustal fault slip rates to geologic rates. However, the slip rates on the trench-perpendicular faults that segment the megathrust do not agree with previously published slip rates. Most models estimate shallow megathrust coupling that is stronger offshore Washington (46-48°N latitude) and northern California (40.5-42°N) than it is offshore Oregon. The coupling distribution on the megathrust is sensitive to fault segmentation, and the greatest differences among models arise in southern Cascadia and offshore Vancouver Island. Slip deficit accumulated on the megathrust can be released via SSEs, impacting the net spatial distribution of coupling over longer time periods. As a consequence, coupling on the megathrust varies temporally. Constraining the spatial distribution of interseismic coupling and its temporal variations that may arise from SSEs can improve our understanding of the seismic hazard in the Cascadia subduction zone.

Session: The Landscape Record of Earthquakes and Faulting - II

Type: Oral

Date: 4/16/2025

Presentation Time: 10:30 AM (local time)

Presenting Author: Hanna

Student Presenter: No

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