Numerical modeling of waves for a tsunami early warning system

Numerical modeling of waves for a tsunami early warning system
4.4 Landslide generated waves along a
straigth beach
This section describes the results of numerical and physical experiments,
which reproduce tsunami generated by landslide partially submerged, which
falls down a sloping straight beach. The analysis of the generated wave
field is given with particular attention to the propagation close to the shore.
Three dimensional physical experiments, performed at the LIAM laboratory
of L’Aquila University, Italy, are described in details in the paper of Di Risio
et al. (2009a). The wave tank has dimensions in plan of 10.8 m in the
long-shore direction and 5.4 m in the cross-shore one, while has a maximum
water depth of 0.8 m. The landslide model is a rigid body, with the shape of
an half of the ellipsoid described by the equation x 2 /a 2 + y 2 /b 2 + z 2 /c 2 =1,
where a =0.2 m, b =0.4 m and c =0.05 m, for a total volume V =0.0084
m 3 . In figure 4.19 is reported a sketch of the landslide model in the plan
view and two transverse sections. The landslide is constrained to slide down
the inclined surface by means of rails. The slope of the coast is of 1/3 (1
vertical, 3 horizontal). The generated water waves are free of propagating
both offshore and alongshore, since the plan dimensions of the used wave tank
are of at least one order of magnitude larger than the width of the landslide,
which can be considered to be a length scale of the waves propagating
alongshore. The experimental study has been carried out reproducing both
subaerial and partially submerged landslides. The wave generation process
is studied by means of video records of the near field and measurements of
the landslide movement; the properties of the waves propagating along the
coast are derived on the basis of runup and water surface level gauges.
A capacitive accelerometer (Metra-Mess CB41) is placed inside the
landslide. The measurement of the acceleration of this body can then be
used to reconstruct, by time integration, its velocity and position in time.
A video camera frames the area where the landslide enters into the water.
A regular grid has been drawn on the slope in order to analyze the image
sequences. The water surface elevation has been measured in the wave tank
by means of traditional resistive wave gauges (resolution of 0.1 mm, noise of
0.3 mm); however the focus of the research is mostly on the run-up along
the coast. In order to measure the instantaneous movements of the shoreline
special wave gauges have been built by the technicians employing two steel
bars (square section of 4 mm x 4 mm) directly embedded into the PVC of
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