TSUNAMI INUNDATION MODELING FOR THE NEW ASCE 7-16 CHAPTER ON TSUNAMI LOADS AND EFFECTS

The recently published update to the American Society of Civil Engineers’ “Minimum Design Loads for Buildings and Other Structures”, commonly referred to as ASCE 7-16, for the first time includes a chapter on tsunami loads and effects. The area of applicability of the tsunami design provisions and the design parameters are based on probabilistic tsunami inundation maps (2,500 year return period) that have been developed for the five states bordering the Pacific Ocean: California, Oregon, Washington, Alaska and Hawai’i.These maps were determined using a two-step approach.

First, we computed offshore probabilistic exceedance amplitudes based on a comprehensive source model that includes all the major subduction zones around the Pacific, with full consideration of aleatory variability in the source and propagation terms as well as epistemic uncertainties. For this analysis, we made use of the fact that wave propagation in deeper water can be represented as a linear process, which allows us to integrate the hazard over thousands of scenarios.

In a second step, we computed inundation maps using a limited set of scenarios, based on the source disaggregation of the first step, using non-linear tsunami propagation models. These propagation computations are much more involved numerically, which is why it is not possible yet to compute the probabilistic inundation directly.

Both the offshore exceedance amplitudes as well as the runup line are included in the ASCE 7-16 tsunami chapter, and are used as constraint in the prescribed procedures for computing the actual design parameters (flow depth and velocity) at the site. We will present examples of these maps and some examples of the computation of site-specific design parameters.