Large-scale numerical modeling of hydro-acoustic waves generated by tsunamigenic earthquakes

Abstract. Tsunamigenic fast movements of the seabed generate pressure waves in weakly compressible seawater, namely hydro-acoustic waves, which travel at the sound celerity in water (about 1500 m s−1). These waves travel much faster than the counterpart long free-surface gravity waves and contain significant information on the source. Measurement of hydro-acoustic waves can therefore anticipate the tsunami arrival and significantly improve the capability of tsunami early warning systems. In this paper a novel numerical model for reproduction of hydro-acoustic waves is applied to analyze the generation and propagation in real bathymetry of these pressure perturbations for two historical catastrophic earthquake scenarios in Mediterranean Sea. The model is based on the solution of a depth-integrated equation, and therefore results are computationally efficient in reconstructing the hydro-acoustic waves propagation scenarios

Real-time inversion of tsunamis generated by landslides

Abstract. In this paper, we test a method for forecasting in real-time the properties of offshore propagating tsunami waves generated by landslides, with the aim of supporting tsunami early warning systems. The method uses an inversion procedure, that takes input data measurements of water surface elevation at a point close to the tsunamigenic source. The measurements are used to correct the results of pre-computed numerical simulations, reproducing the wave field induced by different landslide scenarios. The accuracy of the method is evaluated using the results of laboratory experiments, aimed at studying tsunamis generated by landslides sliding along the flank of a circular shoreline island. The paper investigates what the optimal position is of where to measure the tsunamis, what the effects are, the accuracy of the results, and of uncertainties on the landslide scenarios. Finally, the method is successfully tested using partial input time series, simulating the behaviour of the system in real-time during the tsunami event when forecasts are updated, as the measurements become available

Extended mild-slope equations for compressible fluids

In this paper we derive new forms of the mildslope equation (MSE) for water waves in a weakly compressible fluid on a slowly varying bathymetry, with surface and bottom disturbances. The MSE is a powerful tool to model the refraction-diffraction dynamics of water waves propagating on a variable bathymetry [1]. Traditionally, mild-slope models are derived by assuming that the wave steepness is small, the fluid is inviscid and incompressible and the motion is irrotational. Furthermore, no disturbances are normally considered both on the free surface and at the bottom of the fluid domain [2]. In this paper we shall find new expressions of the MSE by relaxing the incompressibility hypothesis and considering both surface and bottom disturbances. We shall name the set of new formulae as the extended acoustic-gravity mild-slope equations (EAG-MSE). Such a system of equations can be implemented in numerical models for the early detection of coastal flooding based on the hydro-acoustic precursors of surface gravity waves (see [3]–[5])

Inclusion of landslide tsunamis generation into a depth integrated wave model

A numerical model based on the mild slope equation, suitable to reproduce the propagation of small amplitude tsunamis in the far field, is extended to reproduce the generation and the propagation of waves generated by landslides. The wave generation is modeled through a forcing term included in the field equation, which reproduces the effects of the movement of a submerged landslide on the fluid. The measurements of three dimensional laboratory experiments, which simulate tsunamis generated by landslide sliding along the flank of a conical island, are compared with the theoretical calculation results. The present approach is also compared with the similar method of Tinti et al. (2006) used for the generation of these waves in depth integrated model, and the different behavior when using frequency-dispersive and non-dispersive equations is highlighted

Modeling tsunamis generated by submerged landslides using depth integrated equations

We present a depth integrated numerical model for the simulation of the generation and the propagation of tsunamis generated by submerged landslides. The model is able to reproduce at low computational costs the full frequency dispersion of the waves and uses an ad hoc treatment for the incorporation of the effects of the moving seafloor to reproduce the generation of the waves. We also compare the present approach with some simplified techniques used in the past for the generation of these waves in depth integrated models, and we highlight the different behavior of frequency-dispersive and non-dispersive model equations. Reference solutions for comparison and discussion are obtained from the application of a three dimensional solver of the Laplace equation. All the numerical models used in this research are based on linearized model equations and boundary conditions and are therefore expected to provide reliable results for problems involving small amplitude waves and small thickness landslides. The model seems to be useful for rapid and accurate estimation of the properties of landslide generated waves, and can be used to support a tsunami early warning system. (C) 2009 Elsevier Ltd. All rights reserved