Concept of Community Fragilities for Tsunami Coastal Inundation Studies

Abstract

Tsunamis have devastated coastal regions worldwide, with the most recent being the result of the Great Tohoku Japan earthquake and tsunami, which was a M9.0 undersea megathrust earthquake that occurred off the east coast of Japan on March 11, 2011. In this study, a fragility formulation is utilized to develop and illustrate the concept of community fragilities for a community subjected to a wave of a particular height because fragilities are independent of occurrence rate. The fragility formulation for single structures is explained and then extended to the community scale by assigning one of eight archetype structural models and corresponding fragility to each of the buildings in a community. One key feature of the approach is that both the earthquake and tsunami are considered in succession. Three wave forces, i.e., hydrostatic, hydrodynamic, and impulsive wave forces, and the successive hazard loadings, i.e., earthquakes and tsunamis, were considered during the analysis. While debris loading is often critical during inundation, it is not assessed here but should be eventually considered. The tsunami fragility methodology is briefly demonstrated on a single building and then extended to Cannon Beach, Oregon, as an illustrative example. The fragility approach shows that community fragilities follow a similar trend with single structure fragilities and can help with decision making for retrofit and land-use planning. The concept proposed herein can provide a framework regardless of the structural or hydrodynamic model used, provided information on the community is available and a basic understanding of the structure types can be developed.