ИСТИНА

Tsunamis are usually considered as nondispersive long waves. However, tsunamis may exhibit dispersive propagation at a sufficiently great traveling distance L>3/H2, where  is the wave length and H is the ocean depth. In certain cases, when horizontal size of tsunami source turns out to be comparable with ocean depth, manifestations of the phase dispersion one may expect quite close to the source, at distances of tens of kilometers. Tsunami on January 13, 2007 on Central Kuril Islands may serve here as a good example. Its narrow source in conjunction with significant ocean depth (Kuril Trench) provided favorable conditions for manifestations of the phase dispersion before the wave reached the nearest shore situated at 150 km from the tsunami source. Traditional models based on the long-waves theory obviously fails to describe dispersive waves properly. Being dispersive in a deep water region, tsunami while approaching the shore, surely turns into nondispersive wave in shallow water region. We suggest a combined numerical model. Calculation domain is separated into deep and shallow areas by a given isobath. In the deep-water area, waves are described within the framework of the linear potential theory (vertical-resolving model), whereas in the shallow-water area the long-waves theory (vertical-averaged model) is applied. Both models are dynamically coupled along the separating isobath. On the outer (seaward) borders of calculation domain the free-pass boundary condition is imposed. Along the shoreline the normal velocity of water is set to zero. The combined numerical model is applied for simulation of tsunamis occurred on Central Kuril Islands on 15.11.2006 and 13.01.2007.