Numerical modeling of waves for a tsunami early warning system

Numerical modeling of waves for a tsunami early warning system
first stage, before the tsunami event, and to be able to solve in real time the
forecasting calculations. This second part can be computed only if a tsunami
wave detection is available and can be used to correct the pre-calculations of
the a priori stage. It has been discussed the importance of where the tsunami
is detected, i.e. where to locate tidal gauges or pressure sensors. The best
solution would be to have nearshore measurements to forecast the near wave
field, and even offshore measurements in order to register wave features of
tsunami propagating in deep water, since the wave field generated nearshore
presents a wave energy spectrum different from that of offshore wave field.
Furthermore the model is suitable to be applied in real time because is very
robust. After the unit source term computations have been carried out, the
results at the point of interest are obtained also for very unrealistic/noised
input time series. This is what happens in real time when the tsunami is
deteced by tidal gauges: before the signal of the whole tsunami is measured,
the model must have already forecasted the inundation field. The ability
of the model to predict the water surface elevation at one target point, as
the data become available at a gauge close to the generation area, has been
tested in section 5.3.
In the present thesis a model application was highlighted, which is
more suitable to reproduce large geographycal scale tsunami scenarios. It
make use of the matching between the elliptic MSE and its parabolic
approximation, which requires less computations. The elliptic MSE has the
advantage of being able to reproduce diffraction and reflection, but needs
heavier computations; the parabolic MSE has the advantage of being solved
with lower computational costs, but is able to correctly reproduce just the
undisturbed waves propagation. It appeared natural to perform a model
which takes the advantages of using both equation solution, in order to be
accurate and efficient. A simple numerical experiment to test this model
application has been shown. When performing a similar application in a
geographical domain more attention needs to be given. A few examples: the
numerical solution of the parabolic MSE has to take into account when waves
reach a shoreline and stop their propagation; a parabolic approximation
should be solved which allows a wider wave propagation with respect to
the predefined wave motion direction (see the paper of Dalrymple and Kirby,
1988).
All the numerical implementations of the model described here refer
to tsunamis generated by aerial or submerged landslides; however it is
important to keep in mind that the present model can be applied even to
Università degli Studi di Roma Tre - DSIC 107