### Tsunami Waves 7,000 Kilometers from Epicenter

 The BBC reports today of the effect of 3 meter high tsunami waves as far away as the fishing settlement of Hafun, in north-east Somalia, which is located more than 7,000km (4,000 miles) from the epicenter of the earthquake. Pictures from Hafun are available here, and a simple tsunami wave diagram can be found here.

University of Alaska, Fairbanks, has a short note on tsunami waves and the factors affecting their rate of travel and dispersion. However, the focus of this elementary note is on storm-generated waves.

The University of Washington, Seattle, maintains a page on general tsunami information, including a multi-media documentation of recent tsunami events, but no readily available information appears there for calculating the speed and rate of dispersion from a single observation of the wave at a known distance form the epicenter. From what I know about the physics of water waves it should be possible to come up with rough but very useful speed and dispersion estimates based on such (single point w.r.t. epicenter) information. There is a link to tsunami research centers in the U.S. which I didn't have time to pursue in detail.

The USC Tsunami Research Center seems to be the most web-friendly and promising online source of material on tsunami research. It is worthy of further exploration. See, for example, video clips of some simulations for a tsunami event off the coast of California. (If the video simulations included wave amplitude and time progression (or relevant non-dimensional numbers), some non-dimensional analysis could allow rough extensions to similar cases.) Some of the research publications of this center on the analytics of tsunamis should be useful for extracting a simple model to compute speed and dispersion rates. For example, this paper may be start but it considers the case of shallow water wave amplitude evolution. The reference in the paper to "Lamb" is probably to Sir Horace Lamb's seminal work Hydrodynamics of 1879, chapter VIII of which is devoted to the analytical study of tidal waves of various kinds. (I believe Ludwig Wittgenstein studied with Sir Lamb before starting his work with Bertrand Russell.)

While the more fancy analytics and high-compute simulations taking account of coast-line land formations may be of great interest to property insurers and pure scientists, conservative back-of-the-envelope estimates for speed and dispersion of tsunami should still be possible for any middle-schooler to perform and for any fluid dynamics student to explain.

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