Site response analyses for complex geological and morphological conditions: relevant case-histories from 3rd level seismic microzonation in Central Italy

Abstract

The paper presents the results of 5 case studies on complex site effects selected within the project for the level 3 seismic microzonation of several municipalities of Central Italy damaged by the 2016 seismic sequence. The case studies are characterized by different geological and morphological configurations: Monte San Martino is located along a hill slope, Montedinove and Arquata del Tronto villages are located at ridge top whereas Capitignano and Norcia lie in correspondence of sediment-filled valleys. Peculiarities of the sites are constituted by the presence of weathered/jointed rock mass, fault zone, shear wave velocity inversion, complex surface and buried morphologies. These factors make the definition of the subsoil model and the evaluation of the local response particularly complex and difficult to ascertain. For each site, after the discussion of the subsoil model, the results of site response numerical analyses are presented in terms of amplification factors and acceleration response spectra in selected points. The physical phenomena governing the site response have also been investigated at each site by comparing 1D and 2D numerical analyses. Implications are deduced for seismic microzonation studies in similar geological and morphological conditions.

On the Site-Amplification and Soil-Structure Interaction in Urm Structures: Use of Fragility Curves to Assess the Simplified Code-Approach

“…Various reconnaissance studies after seismic events [1,2,3] as well as more specific studies at scale of whole historical centres [4,5,6] testified as the site-amplification effects (either associated to topographic and soil stratigraphic effects) may play a relevant role, together with their vulnerability, in determining the resulting damage levels on existing unreinforced (URM) masonry. The microzonation studies, developed in various area in Italy after the recent seismic events [7,8] that hit the country, confirmed this potential risk factor. Together with this evidence at large scale or on huge building stocks, studies based on detailed models of prototype buildings and more refined analyses methods turn out very useful to understand the phenomenon and also deepen the potential effect of the soil-foundation-structure interaction (SFS).…”

Guest editorial: seismic microzonation of Central Italy following the 2016–2017 seismic sequence

“…According to the Italian approach, the results of all information gathered in the studies are summarized in a Seismic Microzonation map, which is drawn based on the spatial distribution of estimated ground-motion amplification effects. Pergalani et al (2019) provided an overview of the main results and critical issues of the Seismic Microzonation procedure applied to the 138 municipalities of Central Italy. A procedure to obtain SM3 maps with the selection of suitable amplification factors to be used in the identification of areas seismically homogeneous was proposed starting from 1D/2D ground response analyses.…”

“…Finally, Pagliaroli et al (2019) present the results of the ground response analyses performed for 5 complex geological and morphological conditions, selected within the SM project. Implications are then deduced for Seismic Microzonation studies in similar geological and morphological conditions: (1) for slope configurations, 1D analyses could be enough to provide reliable estimation of amplification factors, despite the presence of an inclined bedrock; (2) for ridge configurations, 2D ridge resonance governs the seismic response for periods corresponding to wavelengths comparable with the base size of the relief, exceeding the simplified topographic amplification factors proposed by technical codes; (3) for valley configurations, 2D analyses result mandatory to properly quantify amplification factors at the edge of a large valley, while in the centre of a large valley 2D effects can be neglected.…”

The seismic microzonation study of Pescara del Tronto (Central Italy) during and after the Central Italy earthquake sequence.

“…Looking at shear-waves velocity values in Table 2 the discrepancy between local "geological" and "seismic" bedrock clearly arises, indeed the cover terrains/ geologic bedrock contact surface does not actually correspond to the top of the local seismic bedrock, furthermore the V s contrast between the two geological bedrock units is also significant and only partially expected, since in some sites few kilometers north of Pescara del Tronto (Borgo, San Francesco, Arquata del Tronto cliff) the velocity contrast between the same lithotypes was less pronounced according to L3SM geophysical data (e.g. Giallini et al 2019;Pagliaroli et al 2019;Primofiore et al 2020).…”