Fast evaluation of tsunami scenarios: uncertainty assessment for a Mediterranean Sea database

Abstract

Abstract. We present a database of pre-calculated tsunami waveforms for the entire Mediterranean Sea, obtained by numerical propagation of uniformly spaced Gaussian-shaped elementary sources for the sea level elevation. Based on any initial sea surface displacement, the database allows the fast calculation of full waveforms at coastal sites by linear superposition. A computationally inexpensive procedure is set to estimate the coefficients for the linear superposition. The elementary sources size and spacing is fine enough to satisfactorily reproduce the effects of M >= 6.0 earthquakes. Tsunami propagation is modelled by using the Tsunami-HySEA code, a GPU finite volumes solver for the shallow water equations. Like other existing methods based on the initial sea level elevation, this database is independent on the faulting geometry and mechanism, which makes it applicable in any tectonic environment. However, this is the first time to our knowledge that the uncertainty associated to such a procedure is systematically analysed, and that relatively small earthquakes, which may be relevant in the near field of the source in a complex tectonic setting, are considered. We model a large set of synthetic tsunami test scenarios, selected to explore the uncertainty introduced when approximating tsunami waveforms and their maxima by fast and simplified linear combination. The resulting product is suitable for different applications such as probabilistic tsunami hazard analysis, tsunami source inversions and tsunami warning systems.

Tsunami generation potential of a strike-slip fault tip in the westernmost Mediterranean

“…The combination of this kind of numerical model with an efficient GPU results in a faster than real-time (FTRT) numerical model capable of simulating the generation, propagation and inundation of a tsunami in a region covered by a grid with several million cells in only a few minutes. This model has been extensively validated under the standard benchmarks proposed by the National Tsunami Hazards Mitigation Program (NTHMP) of the U.S.A. 28 , 39 and has been extensively tested in several scenarios and compared with other well-established tsunami models 40 , 41 .…”

Tsunami Generation Potential of a Strike-slip Fault Tip in the Westernmost Mediterranean

“…The combination of this kind of numerical model with an efficient GPU results in a faster than real-time (FTRT) numerical model capable of simulating the generation, propagation and inundation of a tsunami in a region covered by a grid with several million cells in only a few minutes. This model has been extensively validated under the standard benchmarks proposed by the National Tsunami Hazards Mitigation Program (NTHMP) of the U.S.A. 37,38 and has been extensively tested in several scenarios and compared with other well-established tsunami models 39,40 .…”

A New Approximate Method for Quantifying Tsunami Maximum Inundation Height Probability

“…-In regional PTHA, these simulations are barely affordable; therefore, both tsunami time history and g ij are here approximated as a linear combination of unit sources (Molinari et al 2016). Here we introduce z ij as a further source of epistemic uncertainty, which is introduced by combining unit sources rather than simulating all of them as a single source.…”

“…-The correction d à from the empirical distribution d ¼ ðz À gÞ=g. This is the distribution of the relative error of the approximated g values due to the use of unit sources (as defined in Molinari et al (2016), see their Figure 4d). This distribution is obtained by aggregation of a very large number of NLSW simulations with variable source and site, over a quite large range of tsunami intensities (up to [ 10 m), and we may assume that they reasonably approximate this uncertainty source for PTHA purposes.…”