Abstract:
Tsunamis are a critical consideration for design of waterfront facilities in the Pacific Northwest. Structural design for tsunami loading must consider uplift, scour, debris impact, and other effects. If a tsunami is generated by a distant seismic source, such as Alaska subduction zone events, local earthquake shaking does not occur before tsunami inundation. Where local seismic sources can generate tsunamis (e.g. Cascadia Subduction Zone or Seattle Fault), the effects of the preceding earthquake must be considered in tsunami structural design. Earthquake effects can include structural damage and geotechnical impacts, such as liquefaction or lateral spreading.
Seismic ground motions and tsunami wave height are commonly evaluated in separate probabilistic analyses: a probabilistic seismic hazard analysis and a probabilistic tsunami hazard analysis. These analyses produce a relationship between the hazard (ground motion or wave height) and an annual rate of exceedance (or return period). Importantly, the hazard analyses are independent and therefore do not consider the joint probability of a local earthquake producing a tsunami.
This study uses the seismic and tsunami hazard analyses to develop a joint seismic-tsunami hazard model. For a particular probability of exceedance, the joint model produces significantly lower seismic forces and tsunami wave heights than the independent models. The consequences of the lowered seismic and tsunami loads are demonstrated for a site in the Puget Sound Region of Washington State.