Numerical modeling of waves for a tsunami early warning system

Numerical modeling of waves for a tsunami early warning system
the 400 elliptic equations is 4 hours, using the same computer described
before. The numerical results of the overall propagation process appear in
good qualitative agreement with the conclusions of Tinti et al. (2006b).
The tsunami triggered by the subaerial landslide, propagates seawards with
almost circular fronts. The fronts travel more slowly near the Stromboli
coastline. About 4 minutes since the trigger of the tsunami, the entire
Stromboli coast is under the attack of the waves, while the leading wave
is about to hit the northern coast of Panarea (about 20 km South-West of
the Stromboli island). The results of the computations are presented for 4
points of interest (see sketch on Figure 5.7). Point 1 is just at the wave-maker
boundary. Point 2 is South-West of the generation area, in proximity of the
Ginostra village, along the coast. Point 3 is about at the South corner of
the island, in proximity of Punta Lena. Finally the results in proximity of
Basiluzzo, 14 km away from the island are presented at point 4.
Figure 5.8 presents the numerical results in terms of water surface
elevation at the four points introduced above. The fully frequency dispersive
model (thick line) is compared with the linear long waves model (thin line).
At the point 1 appear the sequence of crest-trough of the N-waves imposed
at this point. As the distance from the ‘Sciara del Fuoco’ source grows, the
height of the first positive wave reduces, and it appears other waves following.
It can be noted at the other points 3 and 4, that the first incoming wave is
not the highest. In particular at the point 4, in front of Basiluzzo Island
(the most distant point from the generation area considered here) the first
wave arrives for both models after about 240 s, which is consistent with the
shallow water wave celerity in a constant water depth equal to the mean water
depth between Stromboli and Basiluzzo (about 600 m). Here the results show
significant differences between the two models: in the linear long wave theory
the energy appears to be concentrated at the first incoming waves, while in
the frequency dispersive model results the more dangerous waves are not the
first ones.
The same simulation is now presented in a real time application, in
order to show how the model would work inside an early warning system.
As already introduced the model can be applied in two stages. In the
first computations a tsunami scenario is reproduced assuming to known the
area/boundaries of generation and here imposing a unit source term; in the
second stages the water surface elevation has to be known, i.e. measured,
at some point, in order to calculate the real source term and estimate the
produced wave field. After the a priori tsunami simulations (i.e. unit source
Università degli Studi di Roma Tre - DSIC 100