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Vignaroli, Gianluca
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Vignaroli, Gianluca
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gianluca.vignaroli@unibo.it
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gianluca.vignaroli@igag.cnr.it
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- PublicationRestrictedThe geosciences perspective on seismic response assessment and application to risk mitigation - Guest EditorialEarthquake effects cause dramatic social damage in terms of deaths, injuries and homeless, as well as economic losses when they impact human activities and infrastructures. During the last four decades, the number of people living in areas potentially exposed to earthquakes has almost doubled, as about 2.7 billion people presently reside in seismically active regions. In the period 2001-2020, earthquakes (and tsunamis) were responsible for an average (per year) of 38,000 killed people, more than 6.2 million affected people, and economic losses of about 35 billion US$ (CRED’s Emergency Events Database, 2021; https:// www.cred.be/publications). Not only the most destructive events (e.g., Sumatra 2004, Haiti 2010, Fukushima 2011), but also minor worldwide distributed earthquakes (about 15,000 per year events with magnitude between 7.0 and 4.0) are continuously revealing the essential role of prevention activities devoted to the assessment, management, and mitigation of seismic risk in urban settlements. This is the case of Italy, one of the Mediterranean regions more prone to seismic activity where even earthquakes of moderate magnitude produced dramatic scenarios of devastated villages and loss of lives. The last earthquakes in northern-central Italy (the 2009 Mw=6.1 L’Aquila event, the 2012 ML=5.9. Emilia event, the 2016-2017 up to Mw 6.5 Amatrice-Norcia sequence) severely damaged many residential and strategic infrastructures, and hundreds of people died after the collapses of structures and unreinforced masonry buildings. For these seismic sequences, several technical and scientific activities were carried out in the emergency and post-emergency phases (i) to collect information related the nature and the source of the seismic event (e.g., Lavecchia et al., 2012; Chiaraluce et al., 2017; Wilkinson et al., 2017; Pezzo et al., 2018), (ii) to identify the extent and evaluation of local site effects in comparison to the building damage pattern (e.g., Tertulliani et al., 2012; Douglas et al., 2015), and (iii) to support reconstruction in the damaged settlements (e.g., Moscatelli et al., 2020; Vessia et al., 2021). We learnt from these emergency and post-emergency activities that a strategy for seismic hazard assessment and risk mitigation requires the combination of multidisciplinary and multiscale approaches to manage heterogeneous datasets and procedures, which would provide limited knowledge and ambiguous results if taken separately. A geosciences perspective should aim to overcome these difficulties by integrating specific case histories and methodological approaches to properly investigate the seismogenic process and the site response. Geological, geotechnical, and geophysical data collected during field activities contribute to the formulation of a reliable conceptual model of the subsoil, with a representation of the geological features and the physical and mechanical behaviour of the geomaterials. Based on field data and model results, geoscientists are required (i) to evaluate the ground shaking level at a target site including the soil amplification phenomena due to local geological conditions (Donati et al., 1998; Calderoni et al. 2010; Sarris et al., 2010; Leyton et al., 2013; Fabbrocino et al., 2015; Papadopoulos et al., 2017; Giallini et al., 2020), (ii) to provide map of active faults and their traces at the surface or imaging buried structures (e.g., Ben-Zion et al., 2003; Galli et al., 2014; Tarabusi & Caputo, 2017; Villani et al., 2018), (iii) to assess the liquefaction susceptibility in saturated sandy soils (Wotherspoon et al., 2012; Papathanassiou et al., 2015; Lai et al., 2019), and (iv) to investigate the phenomena related to slope instabilities (Jibson 2007; Terrier et al., 2014; Nowicki et al, 2014; Allstadt et al., 2018; Martino et al., 2020). A geosciences perspective provides the required link between regional-to-local-scale applications and normative/guidelines devoted to the seismic response assessment and risk mitigation, taking advantage of the upgraded competencies in Earth Science disciplines, and connected with the development of new and improved technological instruments for environmental monitoring and laboratory and in-situ testing.
52 26 - PublicationRestrictedThe role of trapped fluids during the development and deformation of a carbonate/shale intra-wedge tectonic mélange (Mt. Massico, Southern Apennines, Italy)(2020-05-18)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; Numerous studies exist on exhumed tectonic mélanges along subduction channels whereas, in accretionary wedge interiors, deformation mechanisms and related fluid circulation in tectonic mélanges are still underexplored. We combine structural and microstructural observations with geochemical (stable and clumped isotopes and isotope composition of noble gases in fluid inclusions of calcite veins) and U-Pb geochronological data to define deformation mechanisms and syn-tectonic fluid circulation within the Mt. Massico intra-wedge tectonic mélange, located in the inner part of the central-southern Apennines accretionary wedge, Italy. This mélange developed by shear deformation at the base of a clastic succession. Deformation was characterized by disruption of the primary bedding, mixing, and deformation of relicts of competent olistoliths and strata within a weak matrix of deformed clayey and marly interbeds. Recurrent cycles of mutually overprinting fracturing/veining and pressure-solution processes generated a block-in-matrix texture. The geochemical signatures of syntectonic calcite veins suggest calcite precipitation in a closed system from warm (108°-147 °C) paleofluids, with δ18O vlaues between þ9‰ and 14‰, such as trapped pore waters after extensive 18O exchange with the local limestone host rock and/or derived by clay dehydration processes at T > 120 °C. The 3He/4He ratios in fluid inclusions are lower than 0.1 Ra, indicating that He was exclusively sourced from the crust. We conclude that: (1) intraformational rheological contrasts, inherited trapped fluids, and low-permeability barriers such as marlyshaly matrix, can promote the generation of intra-wedge tectonic mélanges and the development of transient fluid overpressure; (2) clay-rich tectonic mélanges, developed along intra-wedge décollement layers, may generate low-permeability barriers hindering the fluid redistribution within accretionary wedges.790 9 - PublicationOpen AccessCentral Apennines and its earthquakes: from sedimentology and active tectonics to seismic microzonation studies(2019-09)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; The Central Apennines represents a wonderful record of a still active complex stratigraphic and structural history, as testified by recent earthquakes (L'Aquila 2009, Mw 6.1; Amatrice-Norcia 2016, Mw 6.5). Normal faults activity contributed to the formation of tectonic basins that hosted continental deposits, which recorded the long term traces at surface of large earthquakes. Moreover local seismic amplification has been observed, as result of peculiar geological and structural conditions. The field trip will illustrate examples of earthquake-induced effects due to the recent seismic sequence, in relation to the local stratigraphic and structural setting. The main steps of the geological evolution of Central Apennines, from Jurassic up to the Present, will be investigated which will help define contrasting responses to earthquakes between the cover terrains and the seismic bedrock. Evidences for regional uplift and active faulting, which interplayed with Quaternary climatic changes to feed the mountain chain into its present shape will be illustrated. The effects of recent earthquakes on towns and villages will be described considering the contributon of sediments characterization and the results of the recent advanced seismic microzonation studies.122 93