3D numerical simulation of hydro-acoustic waves registered during the 2012 negros-cebu earthquake

The paper investigates on the hydro-acoustic waves propagation caused by the underwater earthquake, occurred on 6 February 2012, between the Negros and Cebu islands, in the Philippines. Hydro-acoustic waves are pressure waves that propagate at the sound celerity in water. These waves can be triggered by the sudden vertical sea-bed movement, due to underwater earthquakes. The results of three dimensional numerical simulations, which solve the wave equation in a weakly compressible sea water domain are presented. The hydro-acoustic signal is compared to an underwater acoustic signal recorded during the event by a scuba diver, who was about 12 km far from the earthquake epicenter

A NUMERICAL MODEL FOR THE EFFICIENT SIMULATION OF MULTIPLE LANDSLIDE-TSUNAMI SCENARIOS

Submarine landslides can pose serious tsunami hazard to coastal communities, occurring frequently near the coast itself. The properties of the tsunami and the consequent inundation depend on many factors, such as the geometry, the rheology and the kinematic of the landslide and the local bathymetry. However, when evaluating the risk related to landslide tsunamis, it is very difficult to accurately predict all of the above mentioned parameters. It is therefore useful to carry out many simulations of tsunami generation and propagation, with reference to different landslide scenarios, in order to deal with such uncertainties (see for example the probabilistic approach by Grilli et al. 2009). Accurate computations of landslide tsunami generation, propagation, and inundation, however, is computationally expensive, thus limiting the possible maximum number of scenarios. To partially overcome this difficulty, in the present research, a numerical model is proposed that can efficiently compute a large number of tsunami simulations triggered by different landslides. The main goal is to provide a numerical tool that can be used in a Monte Carlo approach framework. Following the study by Ward (2001), we propose a methodology taking advantage of the linear superposition of elementary tsunami solutions

Modal analysis of semi-enclosed basins

Abstract This paper presents a novel technique for the computation of eigenvalues and eigenvectors of partially enclosed basins such as harbours and bays. The procedure makes use of the finite element approximation of the linear shallow water equations, and converts the time-depending problem into an eigenvalues one. The main point of novelty of this research is the mathematical condition used at the boundary that separates the computational domain from the open sea. While classical techniques impose a zero surface elevation (i.e. a nodal line), here an approximate radiation condition is applied. The use of a radiation condition at the open boundary gives a quadratic eigenvalue problem that admits as solution complex eigenvalues and eigenvectors, thus describing the flow in terms of both standing and progressive waves. The new method is applied to an idealized long and narrow harbour, for which an analytical solution of long wave resonance exists, and to the harbour of Marina di Carrara (Italy), for which measurements and previous numerical computation results are available. In both cases the results show good agreement with the available data

a depth integrated equation for large scale modeling of tsunami in weakly compressible fluid

Pressure waves generated by fast seabed movement in weakly compressible sea water, namely hydro-acoustic waves travel at the sound celerity in water (about 1500 m/s). These waves are precursors of the counterpart long free-surface gravity waves and contain significant information on the tsunamigenic source. Measurement of hydro-acoustic waves can therefore anticipate the tsunami arrival and significantly enhance the promptness and accuracy of tsunami early warning systems. In this paper derivation of a novel depth-integrated numerical model for reproduction of hydroacoustic waves is presented and the application of this computationally ecient model on two devastating historical tsunamis of Mediterranean Sea in real bathymetry analyzed to reveal the eect of variable bathymetry. On the basis of the model results, some hints for deep sea observatory are given

Force measurements on storm walls due to overtopping waves: a middle-scale model experiment

The so-called post-overtopping processes are of wide interest for coastal engineers. Dedicated middle-scale tests have been carried out to measure impacts of an overtopped wave on a storm wall at low freeboard coastal structures. A smooth dike slope and a vertical wall, both with a promenade at crest level and a storm wall at the end of it, have been tested in a scale of 1/6. Impacts have been measured both with pressure and force transducers; the two systems provided similar results. A correlation between the hydraulic conditions and the wave impacts on the storm wall is proposed. Further analysis is ongoing to also include the post-overtopping characteristics to increase insight on the acting parameters in this proces

A simplified model of rip currents systems around discontinuous submerged breakwaters

Although in the last years, several numerical models have been shown to be able to reproduce rip currents around discontinuous submerged barriers, only few simple methods of practical use are available for estimating main flow parameters, like the current intensity and the mean water levels, in terms of geometrical (barrier and gap dimensions) parameters and wave characteristics. The aim of this paper is to present a simplified model to be used for an easy estimate of these important rip currents parameters. The model, which is based on rough simplifications, considers the area between the shoreline and the barrier as a reservoir in which water is pumped by breaking short waves across the barrier and from which water flows out at the gap. Four equations (mass and momentum conservation across the barrier, free discharge at the gap and balance of water pumped towards the shore and freely flowing offshore) are used to derive one single model equation that can be solved for the wave set-up and subsequently used for rip current velocity calculation. Two free parameters appear in this equation which respectively account for energy losses at the gap (C-v) and bed friction (mu). The proposed model is validated against available laboratory experiments to show its ability in providing reasonable estimates of the desired parameters, that may be considered by engineers adequate at the preliminary design stage of submerged breakwaters and that can be used for evaluating hydrodynamics on barred beaches. (C) 2004 Elsevier B.V. All rights reserved