Oregon Sea Grant

The 2004 Indian Ocean and 2011 Tohoku tsunami events have shown the destructive power of tsunami inundation to the constructed environment in addition to the tragic loss of life. A comparable event is expected for the Cascadia Subduction Zone (CSZ) which will impact the west coast of North America. Research efforts have focused on understanding and predicting the hazard to mitigate potential impacts. This thesis presents two manuscripts which pertain to estimating infrastructure damage and determining design loads of tsunami inundation.

The first manuscript estimates damage to buildings and economic loss for Seaside, Oregon, for CSZ events ranging from 3 to 25 m of slip along the entire fault. The analysis provides a community scale estimate of the hazard with calculations performed at the parcel level. Hydrodynamic results are obtained from the numerical model MOST and damage estimates are based on fragility curves from the recent literature. Seaside is located on low lying coastal land which makes it particularly sensitive to the magnitude of the events. For the range of events modeled, the percentage of building within the inundation zone ranges from 9 to 88%, with average economic losses ranging from $2 million to $1.2 billion.

The second manuscript introduces a new tsunami inundation model based on the concept of an energy grade line to estimate the hydrodynamic quantities of maximum flow depth, velocity, and momentum flux between the shoreline and extent of inundation along a 1D transect. Using the numerical model FUNWAVE empirical relations were derived to tune the model. For simple bi-linear beaches the average error for the tuned model in flow depth, velocity, and momentum flux were 10, 23, and 10%, respectively; and for complex bathymetry at Rockaway Beach, Oregon, without recalibration, the errors were 14, 44, and 14% for flow depth, velocity, and momentum flux, respectively.