Numerical modeling of waves for a tsunami early warning system

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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
Numerical modeling of waves for a tsunami early warning system earthquakes generated tsunamis. In those cases attention needs to be paid to a different reproduction of the generation mechanism. Normally underwater earthquakes involve the seafloor movement of a larger area, therefore a division of the seismic fault into more segments can be suggested. Since the model equations are linear, the resulting wave field can be calculated by superimposing the solutions of each scenario generated by the movement of a single segment. In view of the implementation of tsunami early warning system, pre-calculated scenarios can be constructed with the tsunamogenic source along all the faults of the sea/ocean of interest. Thus when a tsunami event occurs, its detection in more than one point, with further seismic information, can be used to determine the position of the source and its energy tranferred to the water. Università degli Studi di Roma Tre - DSIC 108
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Università degli studi ROMA TRE Ph
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To my father Michele, my mother Ant
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Abstract A numerical model based on
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Sommario Un modello numerico basato
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Contents 1 Introduction 3 1.1 Tsuna
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List of Figures 1.1 Principal phase
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xiii 4.13 Panels a and b: absolute
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4.32 Comparison of the free surface
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xvii 5.8 Numerical results of the S
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List of Tables 4.1 Radial and Angul
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Numerical modeling of waves for a t
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η1 (m) η2 (m) η3 (m) η4 (m) η5
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Page 77 and 78: η (m) 0.02 0 −0.02 Numerical mod
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Numerical modeling of waves for a tsunami early warning system

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