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Tsunamigenic earthquakes trigger pressure waves in the ocean, given the weak compressibility of the sea water. For particular conditions, a resonant behavior of the water layer can occur, which influences the energy transfer from the sea-bed motion to the ocean. In this paper, the resonance conditions are explained and analyzed, focusing on the hydro-acoustic waves in the proximity of the earthquake area. A preliminary estimation of the generation parameters (sea-bed rising time, velocity) is given, by means of parametric numerical simulations for simplified conditions. The results confirm the importance of measuring, modeling, and interpreting such waves for tsunami early detection and warning.

Detection of low-frequency hydro-acoustic waves as precursor components of destructive tsunamis can enhance the promptness and the accuracy of Tsunami Early Warning Systems (TEWS). We reconstruct the hydro-acoustic wave field generated by the 2012 Haida Gwaii tsunamigenic earthquake using a 2-D horizontal numerical model based on the integration over the depth of the compressible fluid wave equation and considering a mild sloped rigid seabed. Spectral analysis of the wave field obtained at different water depths and distances from the source revealed the frequency range of low-frequency elastic oscillations of sea water. The resulting 2-D numerical model gave us the opportunity to study the hydro-acoustic wave propagation in a large-scale domain with available computers and to support the idea of deep-sea observatory and data interpretation. The model provides satisfactory results, compared with in situ measurements, in the reproduction of the long-gravitational waves. Differences between numerical results and field data are probably due to the lack of exact knowledge of sea bottom motion and to the rigid seabed approximation, indicating the need for further study of poro-elastic bottom effects.

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.

The paper presents a numerical model to reproduce the tsunami generation and propagation, which can be applied in real-time to be used as a forecasting tool. Free surface elevation measurements in a point close to the tsunami generation area, allows the real-time prediction of tsunami in the far field. This is possible due to an inversion technique. The measurements and modeling of hydro-acoustic waves could shorten the time for spreading the alarm and reduce the number of false alerts. In the paper new investigation about hydro-acoustic waves are also presented in order to outline their possible use to support Tsunami Early Warning System.