In the creation of “surprise tsunami”, submarine landslides head the suspect list. Moreover, improving technologies for seafloor mapping continue to sway perceptions on the number and size of surprises that may lay in wait offshore. At best, an entirely new distribution and magnitude of tsunami hazards has yet to be fully appreciated. At worst, landslides may pose serious tsunami hazard to coastlines worldwide, including those regarded as immune. To raise the proper degree of awareness, without needless alarm, the potential and frequency of landslide tsunami have to be assessed quantitatively. This assessment requires gaining a solid understanding of tsunami generation by landslides, and undertaking a census of the locations and extent of historical and potential submarine slides. This paper begins the process by offering models of landslide tsunami production, propagation and shoaling; and by exercising the theory on several real and hypothetical landslides offshore Hawaii, Norway and the United States eastern seaboard. I finish by broaching a line of attack for the hazard assessment by building on previous work that computed probabilistic tsunami hazard from asteroid impacts.
Earthquakes generate most tsunami. Rightly so, tsunami research has concentrated on the hazards posed by seismic sources. The past decade however, has witnessed mounting evidence of tsunami parented by submarine landslides. In fact, submarine landslides have become prime suspects in the creation of “surprise tsunami” from small or distant earthquakes. As exemplified by the wave that devastated New Guinea's north coast in 1998 (Tappin, et. al., 1999; Geist, 2000), surprise tsunami can initiate far outside of the epicentral area of an associated earthquake, or be far larger than expectedgiven the earthquake size. In contemplating the great number and im-mense extent of seabed failures known to have frequented recent geological history, the biggest surprise just may arrive without any precursory seismic warning at all a tsunami sprung from a spontaneous submarine landslide.
The geography of earthquakes only casually resembles the geography of submarine landslides. Tsunami excitation mechanisms between earth-quakes and landslides differ substantially too. Accordingly, an entirely new distribution and magnitude of tsunami hazards has yet to be fully appreciated. Landslides may pose perceptible tsunami hazards to areas regarded as immune – the Gulf of Mexico, the North Sea, or the eastern seaboard of the United States. Many of these areas, unaccustomed to earthquakes and earthquake tsunami, lie on flat and passive continental margins. A 5-meter sea wave striking there would over-run far more territory than a similar wave hitting a rugged shore, such as California's north coast.
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