No natural disaster in modern history has impacted a broader region, or impacted more lives in more diverse communities, than the 2004 Indian Ocean tsunami. For many, this disaster redefined the scale of conceivable impacts of natural disasters. The scales of natural processes that contributed to this disaster were equally tremendous, including the magnitude of the tsunamigenic earthquake, the largest on Earth since the Chilean earthquake of 1960; the volume of water displaced during the earthquake and the speed with which the resulting wave could traverse an entire ocean basin; and the force and extent of the wave runup where the tsunami reached coastal areas. Yet on geological timescales, such events are common.

We must prepare for such natural events. In the context of nuclear facilities, preparation involves understanding, or forecasting, the impact of potential tsunami on coastal sites (McKinley and Alexander, Chapter 22, this volume). This includes developing an understanding of the sources of tsunami, the propagation of tsunami waves, and their wave height, wavelength and runup. This chapter reviews tsunami processes, and introduces the concept of probabilistic tsunami hazard assessment, parallel to other types of hazard analysis already common for nuclear facilities.

What is a tsunami?

Tsunami comes from the Japanese word meaning “harbor wave.” In Japanese, the word tsunami is the same in both the singular and plural form. In English tsunamis is often used for the plural, although both tsunami and tsunamis are correct.Atsunami is a series of waves that are rapidly generated when a large volume of water (e.g. a lake, the sea, the ocean) is vertically displaced by an impulse disturbance such as an explosion, earthquake, volcanic eruption, landslide or meteorite impact.