Multisource Bayesian Probabilistic Tsunami Hazard Analysis for the Gulf of Naples (Italy)

Abstract

A methodology for a comprehensive probabilistic tsunami hazard analysis is presented for the major sources of tsunamis (seismic events, landslides, and volcanic activity) and preliminarily applied in the Gulf of Naples (Italy). The methodology uses both a modular procedure to evaluate the tsunami hazard and a Bayesian analysis to include the historical information of the past tsunami events. In the SourceModule the submarine earthquakes and the submarine mass failures are initially identified in a gridded domain and defined by a set of parameters, producing the sea floor deformations and the corresponding initial tsunami waves. Differently volcanic tsunamis generate sea surface waves caused by pyroclastic density currents from Somma‐Vesuvius. In the PropagationModule the tsunami waves are simulated and propagated in the deep sea by a numerical model that solves the shallow water equations. In the ImpactModule the tsunami wave heights are estimated at the coast using the Green's amplification law. The selected tsunami intensity is the wave height. In the BayesianModule the probabilistic tsunami analysis computes the long‐term comprehensive Bayesian probabilistic tsunami hazard analysis. In the prior analysis the probabilities from the scenarios in which the tsunami parameter overcomes the selected threshold levels are combined with the spatial, temporal, and frequency‐size probabilities of occurrence of the tsunamigenic sources. The prior probability density functions are integrated with the likelihood derived from the historical information based on past tsunami data. The posterior probability density functions are evaluated to produce the hazard curves in selected sites of the Gulf of Naples.

On the landslide tsunami uncertainty and hazard

“…To this end, just a handful of landslide probabilistic tsunami hazard analysis (PTHA or LPTHA) studies also quantifying the temporal probability of tsunamis exists in the scientific literature, e.g. Grezio et al 2012, Lane et al 2016and Grezio et al 2020. However, none of the landslide PTHA studies to date appropriately addresses tsunami uncertainty due to the unknown variability in landslide dynamics.…”

Probabilistic Tsunami Hazard and Risk Analysis: A Review of Research Gaps

“…Volcanic PTHA, coined VPTHA here, is even less developed than LPTHA (Grezio et al, 2017). Among the few examples are the VPTHA framework developed in Ulvrova et al (2016) and Paris et al (2019) for underwater explosions at Campi Flegrei, and Grezio et al (2020) for pyroclastic flows of Vesuvius. Given that risk reduction measures at volcanoes are often related to the identification of precursory patterns preceding eruptions or to recognizing unrest episodes with increased volcanic activity, the volcanic hazard is often computed conditional to eruptions or unrest, and without an explicit quantification of long-term probability.…”

“…This difficulty leads to simplified modeling schemes (e.g., Bevilacqua et al, 2017;Sandri et al, 2018). These simplified strategies may be too reduced for an effective constraint of their tsunami potential (Grezio et al, 2020). Some phenomena may be represented by empirical models (for submarine explosions, see Paris et al, 2019, and for caldera collapse, see Ulvrova et al, 2016).…”

Tsunami risk management for crustal earthquakes and non-seismic sources in Italy

“…Vesuvius is responsible for the largest part of the historical tsunamis reported in EMTC: the two most famous and catastrophic eruptions occurred on 24 August 79 AD and on 17 December 1631 are both reported to have been accompanied by significant sea movements. A short review of the numerical simulations of pyroclastic flow impact and consequent tsunami generation in the Gulf of Naples can be found in [46,98,321].…”

“…Tsunami early warning and hazard assessment from non-seismic sources such as landslides and volcano flank instabilities, which are closely related phenomena, are less developed than their seismic equivalents. Consequently, despite few prototypal examples of PTHA including non-seismic sources exist [11,17,32,98], a standardized approach to model the hazard and manage the warnings for tsunamis caused by such non-seismic sources does not exist (e.g. [11,17,54,65]).…”