FY 2026

The impact of 3D structure on coseismic coastal land-level change and tsunami generation in the Cascadia Subduction Zone

Dunham, A., J. Kim, E. Wirth, D. Schmidt, R. LeVeque, Y. Wei, L. Adams, and F. Polliz

Geophys. Res. Lett., 52(24), e2025GL117783, doi: 10.1029/2025GL117783, View open access article at AGU/Wiley (external link) (2025)

Estimates of coseismic vertical displacements from past and potential future subduction zone earthquakes provide critical constraints on regional seismic and tsunami hazard. Many studies use elastic homogeneous half-space models to calculate vertical displacements from a specified earthquake slip distribution, neglecting complexities of 3D structure in subduction zone settings. Here, we use 3D ground motion simulations of potential Cascadia Subduction Zone earthquakes to investigate the impact of realistic 3D Earth structure on estimated vertical displacements. We show that offshore uplift increases when including 3D structure due to high fault slip in low-rigidity accretionary wedge sediments and coastal subsidence decreases due to higher rigidity material at depth. These larger offshore uplifts cause increased tsunami maximum wave heights, and coastal subsidence at paleoseismic sites decreases on average by ∼17 cm, or ∼60%, which can have important implications for the amplitude and extent of slip in earthquake scenarios developed based on paleoseismic data constraints.

Plain Language Summary. Estimating the expected shaking from a future earthquake or inundation from a tsunami can help prepare for these hazards and make our society more resilient. However, different techniques can yield different results and impact the estimated hazard. In this study, we investigate how different modeling approaches influence the estimation of coseismic land-level change due to hypothetical earthquake scenarios in the Cascadia Subduction Zone. We find that including realistic 3D Earth structure, as opposed to uniform properties, results in less coastal subsidence and more offshore uplift during an earthquake. By comparing our estimates to coastal geologic evidence from past earthquakes and incorporating them into tsunami simulations, we demonstrate the impacts of using realistic 3D Earth structure on both seismic and tsunami hazard estimates.