GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.1 GNGTS 2024 The study area L’Aquila downtown is placed in the L'Aquila-Scoppito intermontane basin (ASB) which is a half- graben bordered by SW-dipping normal mostly actve faults located in its northern border, which are responsible for the historical and present seismicity. ASB is flled with approximately maximum 600 meters of Plio-Quaternary contnental slope, colluvial and alluvial deposits which overlie unconformably the carbonate bedrock formed by Jurassic to Miocene marine carbonate units (Antonielli et al., 2020; Fig. 3). Heterometric breccias with clayey-silty matrix (S. Demetrio-Colle Cantaro Unit) represent the frst Plio-Quaternary detrital sedimentaton in the ASB. These lithologies and the underlying bedrock are unconformably overlain by alluvial and marshy deposits composed by silt, clay, and sands (Madonna della Strada Unit – MDS, Early Pleistocene) (Tallini et al., 2019). The Fosso di Genzano Unit (FGS), incised into the earlier deposits, is composed by gravel and sand, pertaining to Middle Pleistocene alluvial fans. The shallow part of the gently S-dipping hill, in which L’Aquila downtown is located, is mainly composed by 20-100 m-thick of L'Aquila Breccia Unit (LAB). LAB lays unconformably upon FGS and MDS and consists of heterometric poorly sorted carbonate clasts, sometmes with sandy- clayey calcareous matrix sedimented during the Middle Pleistocene with rock-avalanche process (Antonielli et al., 2020). In the southern part of L’Aquila hill, alluvial lens of sand and gravel (ALE) is interlayered within LAB (Fig. 3). The Red Soil Unit (RS) covers unconformably LAB (Tallini et al., 2020). RS includes reddish clayey colluvial sediment and epikarst deposits and exhibits highly variable thickness, reaching up to 30 meters. RS formed during a humid and warm interglacial phase of the Upper Pleistocene at the expense of LAB. Data about geological features potentally controlling subsidence processes To perform a geological and seismic characterizaton of the study area, a total of 142 Shear Wave Velocity (Vs) in-situ measurements, pertaining to the shallow lithologies within LAHC, were acquired from bibliographic sources (e.g., Amoroso et al., 2018). Furthermore, logs from an extensive dataset of 573 boreholes, many of which were drilled afer the 2009 earthquake to facilitate the reconstructon of LAHC buildings, were integrated with geological data from the literature (e.g., Tallini et al., 2020). The collected data formed a substantal database that facilitated numerous GIS-based processing, aimed to assess the surface geology and the RS thickness (Sciortno et al., 2023). Due to their high compressibility, RS have been recognized in various studies as lithology responsible for site- specifc seismic amplifcatons (e.g., Tallini et al., 2020). The produced geological map was rasterized, assigning a Vs (Shear Wave Velocity) value to each lithology based on literature data from Downhole (DH) and MASW in situ measurements (e.g., Amoroso et al., 2018). Geomorphological and hydrogeological characterizaton of the LAHC area were carried out through the analysis of a digital terrain model (DEM) and of the piezometric level.