When probabilistic seismic hazard climbs volcanoes: the Mt Etna case, Italy – Part 2: computational implementation and first results

Abstract

Abstract. This paper describes the model implementation and presents results of a probabilistic seismic hazard assessment (PSHA) for the Mt Etna volcanic region in Sicily, Italy considering local volcano-tectonic earthquakes. Working in a volcanic region presents new challenges not typically faced in more standard PSHA, which are most broadly due to the nature of the local volcano-tectonic earthquakes, the cone shape of the volcano, and the attenuation properties of seismic waves in the volcanic region. These have been accounted for through the development of a seismic source model that integrates data from different disciplines (historical and instrumental earthquake datasets, tectonic fault data, etc. presented in a companion paper Part I, Azzaro et al., 2017), and by the development and software implementation of original tools for the computation, such as a new ground-motion prediction equation and magnitude-scaling relationship specifically derived for this volcanic area, and the capability to account for the surficial topography in the hazard calculation, which influences source-to-site distances. Hazard calculations have been carried out using two widely used PSHA software packages (CRISIS, Ordaz et al., 2013; the OpenQuake-engine, Pagani et al., 2014). Results are referred to short to mid-term exposure times (10 % probability of exceedance in 5 and 30 years, Poisson and time-dependent) and spectral amplitudes of engineering interest. A preliminary exploration of the impact of site-specific response is also presented for the most densely inhabited region, and the variability in expected ground motion is finally commented. These results do not account for the M > 6 regional seismogenic sources that dominate the PSHA at long return periods, but present a different viewpoint that we believe is also relevant for retrofitting of the existing buildings, and for driving impending interventions of risk reduction.

The Use of Continuous Wavelet Transform for Ground-Roll Attenuation

“…This technique firstly introduced by Nogoshi and Igarashi (1971), was put into practice by and became in recent years widely used since it provides a reliable estimate of the fundamental frequency of soft soil deposits. The good agreement observed between results obtained using earthquake records and ambient noise has pointed out that microtremors are a valid tool to investigate ground motion polarization properties Di Giulio et al, 2009;Panzera et al, 2017). Crisci et al, 2008).…”

“…Complex earthquake source models have being increasingly incorporated in probabilistic seismic hazard assessment (PSHA) by some countries. In Italy, we recently included in the modelling realistic geological complexities of non-rectangular faults, rough topography, and departure from traditional stationary assumptions, as is required during an ongoing seismic sequence or in volcanic contexts Peruzza et al, 2016Peruzza et al, , 2017. We briefly present an aftershock PSHA (sensu Yeo and Cornell, 2009) case study in Italy and the lessons learnt from it.…”

“…The H/V spectral ratio (HVSR, of background seismic noise is probably the most used and efficient technique to estimate the site response in case of simple layered structures, overcoming the use of a reference site. Site effects can also modify the polarization of particle motion due to the proximity of fault damage zones (Pischiutta et al, 2017;Panzera et al, 2017) and topographic irregularities Pischiutta et al, 2010;Formisano et al, 2012). Accross fault zones the horizontal polarization of seismic signals usually shows high angle respect to the fault strike direction.…”

Numerical Site Spectral Amplification Due to Structural Control of Shallow Faults in Wadi Natash, Eastern Desert, Egypt

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Recently, studies by [2] and [3] have focused on analyzing the site effects due to the presence of fault zones. Ground motion amplification of directional effects along a polarized horizontal component could be observed because of active faults and extended fractures (e.g.

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