GNGTS 2024 - Atti del 42° Convegno Nazionale
Session 2.2 GNGTS 2024 Figure 1b shows an updated version of the map of slope resistance demand. It relies on more recent informaCon and tools, namely the ZS9 seismogenic zonaCon (Melem et al., 2004), the latest abenuaCon relaCon for Arias Intensity published by Sabeba et al., (2021) and the sopware R-CRISIS for the seismic hazard assessment (Ordaz et al., 2017). A comparison of the two maps reveals significant differences, in parCcular an increase of the maximum value of (A c ) 10 from 0.04 to 0.06 g. The spaCal distribuCon of (A c ) 10 values is strongly influenced by the geometry of the seismogenic zones, which cause a minimum in the central part of Daunia and higher values both in the northern and southern parts. Higher (A c ) 10 values coincide with the areas including many old, large deep-seated landslides of unknown origin (Ardizzone et al., 2023). These landslides are generally larger than the recent slope failures triggered by rainfall, and Wasowski et al. (2022) presented circumstanCal evidence for their co-seismic origin. Data on site resonance properHes Our previous study on slope resistance demand in Daunia have not incorporated the effect of site amplificaCon. At present, a sopware package like R-CRISIS allow taking into account the site effects providing in input a matrix of the spaCal distribuCon of amplificaCon factors. A detailed evaluaCon of such effects requires the acquisiCon of many data, which is not feasible for regional scale studies. Thus, for a preliminary esCmate of the influence of site effects on slope resistance demand, we explore the uClity of informaCon on site resonance properCes obtained from ambient noise analysis carried out during the 1 st level of Seismic MicrozonaCon of the Daunia urban and peri-urban areas. A large set of noise recordings (about 1000) have been acquired on different lithologies and slope stability condiCons. We iniCally examined the results obtained from their processing with the HVNR method (Nakamura, 1989), which idenCfies local site condiCons from peak values in the raCos between the spectral amplitudes of the horizontal and verCcal components of the recordings. For each Daunia municipality, the resonance amplitudes and frequencies and the lithology at the measurement sites were idenCfied, disCnguishing whether these sites are on landslide or stable areas. The following flysch formaCons are most common at the measurement sites: FAE - Flysch di Faeto (Upper Burdigalian-Lower Tortonian). Limestone-marly-clayey alternaCon with a bentonite base. It is divided into a predominantly peliCc facies (FAEp) and a predominantly calcareniCc facies (FAEc). FYR – Flysch Rosso (Cretaceous-Aquitanian). Grey-green to reddish mudstones alternaCng with blackish layers of jaspers, with intercalaCons of breccias, calcarenites and calciluCtes. Fig. 2 shows the distribuCon of resonance frequencies and H/V peak amplitudes resulCng from noise measurements. The most recurring frequencies are between 0.9 and 4 Hz, while the most recurrent peak amplitudes are between 2 and 4. The abenCon is focused on sites
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