A Probabilistic Framework for Coseismic Tsunami Design-Paper

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The paper presents a probabilistic framework for evaluating earthquake shaking and tsunami inundation as a coupled hazard. Conventional seismic and tsunami hazard analyses treat the events independently, even when a nearby earthquake could generate a tsunami. Combining their separate design-level demands can therefore pair loads from different, unlikely-to-co-occur events and produce overly conservative estimates of sequential loading.<br /><br />The proposed method extends probabilistic seismic and tsunami hazard analysis to calculate the likelihood of jointly exceeding specified ground-motion and tsunami-amplitude thresholds. It accounts for earthquake magnitude and distance, ground-motion and tsunami models, and the correlation between shaking and tsunami amplitude. Because no established correlation model is available, the authors test a range of correlation coefficients and recommend using an envelope of the resulting hazard curves.<br /><br />The framework is applied to the Friday Harbor Ferry Terminal in Washington State, considering Cascadia Subduction Zone earthquakes. The results show that conditional tsunami hazard decreases as the accompanying spectral acceleration increases: large shaking and large inundation at the site are both possible, but their joint occurrence is relatively unlikely. For a 2,475-year return period, independent analyses give a 5-second spectral acceleration of 0.051 g and a tsunami amplitude of 6 m. A joint-hazard combination with 0.04 g shaking corresponds to a tsunami amplitude of 3.7 m.<br /><br />The authors emphasize that structures must still be designed to resist the independent seismic and tsunami loads. The framework instead refines assessment of their combined, sequential effects, which may include earthquake-related structural damage, liquefaction, and lateral spreading before tsunami loading. Further work is needed to establish appropriate design combinations and correlation models.

Keywords

earthquake shaking

tsunami inundation

probabilistic hazard analysis

coupled hazard

joint exceedance

seismic hazard

tsunami hazard

Cascadia Subduction Zone

spectral acceleration

Friday Harbor Ferry Terminal