GNGTS 2016 - Atti del 35° Convegno Nazionale

GNGTS 2016 S essione 2.2 415 Results from the first level of the seismic microzoning Sulmona urban area. According to the GdL MS (2008), the objective of the first level of microzoning activity is to identify portions of territory that are characterized by a homogeneous seismic behaviour (MOPS) based on geological and geotechnical data gained by past investigations supported by local administrations that appointed local professionals and new quick investigations (for example noise measurements). Past investigation campaigns have been generally undertaken for other purpose than the seismic microzonation. These characterization campaigns are commonly used to get information of the lithotypes and stratigraphic succession near the surface although they were commonly performed for other purposes than to collect physical and mechanical dataset of soil properties useful for dynamic characterization. This is the main reason why, at level 1, a few data are available of physical and mechanical values of soil properties to estimate the liquefaction susceptibility of soils. Concerning the level 1 microzoning at the intramontane Sulmona basin, based on past in field data, high local seismic amplifications are expected due to the presence of complex geological, geomorphological and tectonic features. In fact, it shows an asymmetric half-graben-like geometry (Fig. 1c). The deepest available borehole passes through a 435 m of continental deposits but not reaching the carbonate bedrock. The continental Fig. 2 – Simplified stratigraphic logs of the two investigated wells (S1 and S2; see Fig. 1 for their locations). a) S1 is deepened to the valley floor and intercepts the water table. It passes through recent fine grained alluvial deposits laying above mud and clays lacustrine deposits, in an area identified as a liquefaction prone area, near the railway station. b) S2 is located in the historic center of the Sulmona town in alluvial deposits constituted by gravels and sands passing to lacustrine deposits. This passage always shows a velocity value inversion. The code spectrum related to the SLV ultimate limit state is overpassed over the whole interesting range of periods (0.1-1 s) by the median of the spectra calculated through the numerical simulations of local seismic responses. c) The profile of the factor of safety against liquefaction (FSL) calculated at S1 site. The calculations performed here, based on preliminary analyses, show that site S1 is not susceptible to liquefaction.