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Scenario ShakeMaps for Cascadia Subduction Zone Megathrust Earthquakes Using 3D Ground Motion Simulations

Description: 

The U.S. Geological Survey develops scenario ShakeMaps for hypothetical future earthquakes using shaking estimates from empirical ground motion models (GMMs) or simulations. These scenario ShakeMaps are critical products that are used by communities for emergency response planning and public outreach. Although GMM-based scenario ShakeMaps are most common, they can lack critical features that impact seismic hazard estimates, such as 3-D basin effects and regionally specific rupture characteristics. Here, we develop scenario ShakeMaps for the Cascadia Subduction Zone (CSZ) earthquakes using ground shaking information from 36 full-margin 3D broadband simulations.

To develop broadband synthetic ground motions, we use a hybrid approach that combines (1) low-frequency (< 1 Hz) deterministic synthetics calculated in a 3D seismic velocity model with (2) high-frequency (1-10 Hz) stochastic waveforms using a 1 Hz matched filter. The earthquake scenarios are built using a logic tree approach, varying the up and downdip limits of slip, hypocenter location, slip distribution, and event magnitude (M8.7-9.2). Due the minimum shear wave velocity used in the simulations of 600 m/s, we incorporate site adjustments using regional Vs30 values and soil velocity profiles. With these scenario ShakeMaps, we examine inter- and intra-event variability to highlight the impacts of rupture characteristics and 3D velocity structure on ground motion variability. We also compare our ShakeMaps to GMMs developed for Cascadia interface earthquakes, showing that utilizing 3D simulations has a profound impact on regional hazard estimates. These scenario ShakeMaps are the first step in building multi-hazard maps to quantify the regional impacts of ground shaking and cascading hazards such as tsunami inundation, landslides, liquefaction and land-level change.

Session: Advancing Seismic Hazard and Risk Assessment through Multi-Disciplinary Approaches - I

Type: Oral

Date: 4/15/2026

Presentation Time: 11:15 AM (local time)

Presenting Author: Audrey Dunham

Student Presenter: No

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