Simulation-Based Scenario ShakeMaps for Large Magnitude (Mw 6.5+) Crustal Earthquakes on the Seattle, Tacoma, and Southern Whidbey Island Faults, Washington, USA

ABSTRACT Scenario ground-motion maps based on empirical ground-motion models (GMMs) provide a rapid and generally reliable means of estimating the amplitude and distribution of earthquake shaking. However, because GMMs are designed for broad applicability, they often rely on simplified representations of Earth structure, which can limit their accuracy in regions with complex source, path, and site effects. This can substantially impact the accuracy of predicted shaking in areas like western Washington State, where deep, interconnected basin structure exerts a strong influence on seismic-wave propagation. In this study, we present a new suite of simulation-based scenario ShakeMaps that characterize ground shaking from large-magnitude (Mw 6.5–7.5) earthquakes on the Seattle, Tacoma, and southern Whidbey Island faults. These maps are developed using results from recent 3D wave propagation simulations (Stone et al., 2022, 2023, 2025) that incorporate realistic rupture geometries, variable slip distributions, and a regional 3D seismic velocity model with shallow soils. Broadband ground motions are estimated by combining the low-frequency (