An earthquake with surface magnitude (Ms ) 7.0 occurred 100 km off the Nicaraguan coast on September 2, 1992 (GMT). Despite its moderate size, this earthquake generated a sizable tsunami, which caused extensive damage along the coast of Nicaragua. In late September, about 170 people, mostly children, were listed dead or missing; 500 were listed injured; and over 13,000 were listed homeless, with more than 1500 homes destroyed. Damage was the most significant since the 1983 Japan Sea earthquake tsunami, which killed 100 people in Japan. The Flores (Indonesia) earthquake and tsunami of December 12, 1992, were more destructive than the Nicaragua or Japan Sea events.

Dominant periods determined from tide gauge records of the 2004 Sumatra tsunami were used to estimate the size of the tsunami source. A period of 40 minutes dominates the initial motions and spectra are consistent with a fault width of 110 km for a sea depth of 1000 m. Another dominant period of 140 minutes in the spectra observed at the direction of fault azimuth can be explained using a fault length of 1200 km. These values taken together are consistent with source formation on the continental slope with width of 110 km and length of 1200 km along Nicobar and Andaman Islands.

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An edge wave traveling along a continental shelf with a sloping region sandwitched by a flat shelf and an ocean bottom is investigated theoretically by estimating the dispersion relation and the amplitude distribution versus the distance from the coast.The results are discussed in comparison with a step shelf model.It is demonstrated that dispersion curves shifted toward a long period range with decrease of a dip angle of a sloping region and that the minimum point of a group velocity curve becomes less clearer in the case of a sloping model. It is found that the maximum amplitude of the Kamchatka tsunami observed in Japan can be accounted for by an edge wave propagated along the shelf. The result is useful for predicting arrival time of the maximum amplitude for a distant tsunami with an oblique incidence to the continental shelf.Edge wave has so far been studied by many investigators. For examples, SEZAWA and KANAI (1939) pointed out an analogy between edge wave on a shelf with a step and Love wave in seismology. REID (1958) estimated the effect of Coriolis force on an edge wave on a sloping shelf. NAKAMURA (1962) theoretically investigated generation of edge wave on a continental shelf for a cylindrical source and obtained a theoretical marigram. HATORI and TAKAHASI (1964) applied the dispersion relation by NAKAMURA (1962) to the Iturup tsunami of 1963. AIDA et al. (1968) investigated an edge wave traveling along a curved shelf experimentally. MUNK et al. (1964) discussed trapped and leaky modes on the continental shelf off California using the shelf profile approximated by a series of steps. Generally a typical continental shelf is approximated by a linear slope and a fairly uniform profile over a long distance. Thus a linear sloping model is considered to be appropriate for a typical shelf like the Pacific shelf of north east Japan. Therefore, it is of significance to obtain analytical solutions for a linear sloping model between two flat regions. Such analytical solutions make it easy to investigate the property of the model and to compare theoretical results to observed ones.