Search

On December 29th, 2020, a strong Mw 6.4 earthquake hit central Croatia. The epicenter was located approximately 3 km southwest of Petrinja, and the intensity was estimated to VIII-IX EMS. The earthquake led to significant environmental effects related to earthquake magnitude, focal depth, and geological and geotechnical properties of the affected area.The Croatian Geological Survey (HGI-CGS) conducted extensive geological and geodetic surveys starting a few hours following the main shock to measure the earthquake’s effects,including those on infrastructures. Ten geologists from the Department of Geology carried out surveys from Decmber 31st, 2020 to January 7th, 2021 along the potential seismogenic source (inferred from geological maps and InSAR data) and in the wider epicentral area that suffered significant damage (e.g., Glina and Sisak).During a second phase, researchers from the University of Zagreb (PMF UniZG), Slovenia (GeoZS), Italy (INGV, ISPRA, U. Chieti) and France (CEREGE, IRSN) were mobilized to complete the observations. The collaboration with these geologists allowed to deepen the investigations and to bring further detail to quantify the effects. The surveys were then compiled based on data formats used by the European Community, namely those of the INGV EMERGEO team (Villani et al., 2017; for environmental effects including surface ruptures and liquefaction) and those of the SURE group (Baize et al., 2019 for surface ruptures).These observations revealed that the earthquake triggered a discontinuous, few km-long surface rupture with a maximum displacement of about 20 cm, which is consistent with the lower average of observations made on similar events (Wells and Coppersmith, 1994). Liquefaction spread over several tens of square kilometers mostly in river plains, the most distant being about 20 km from the epicenter (to be confirmed!). Other observed effects include lateral spreading, landslides, groundwater regime changes, rockfalls, and various infrastructure damage.The compilation of the acquired dataset into a unified database, consistent with database of other historical and recent events, is essential for establishing reliable empirical relations between geological effects and physical characteristics of earthquakes (magnitude, depth). This forms the basis for seismic hazard assessments, whether for “surface rupture”, “liquefaction”, or “ground-shaking” potential.

On December 26, 2018, the largest instrumental earthquake ever recorded in Mt. Etna (Sicily, southern Italy) shook the eastern flank of the volcano, with epicenter near the Fleri village along the right-lateral Fiandaca Fault (focal depth less than 1 km, Mw 4.9). The mainshock was accompanied by widespread surface faulting. We surveyed and mapped the coseismic ground ruptures and collected structural data on their orientation, displacement and fabric at surface. We compared the fault zone characteristics with near surface and deeper driving factors (topography and morphology of the buried top of sedimentary basement). The shallow geological layering underneath influenced the surface expression of faulting during the 2018 event: the top surface of the basement could be considered as a detachment surface for a shallow sliding block. The earthquake occurred on top of a depression of the sedimentary basement forcing the sliding eastward, causing at surface the re-arrangement of the fault strand pattern and deformation style, switching from shear faulting to a tensile failure. The Fleri earthquake therefore provides an unprecedented dataset for understanding 1) active faulting in the European largest onshore volcano, 2) the complex dynamics of this edifice, and 3) contributing to a more refined seismic hazard assessment.

Il progetto RETRACE-3D (centRal italy EarThquakes integRAted Crustal modEl) è volto alla caratterizzazione tridimensionale, geologica e sismotettonica, del volume di crosta terrestre che a partire dal 24 agosto 2016 è stato interessato dai terremoti di Amatrice, Visso e Norcia, e dalla relativa sequenza sismica. Il progetto è il risultato di una collaborazione tra il Dipartimento della Protezione Civile, l’Istituto Nazionale di Geofisica e Vulcanologia (INGV), il Consiglio Nazionale delle Ricerche che partecipa con l’Istituto di Geologia Ambientale e Geoingegneria (CNR-IGAG) e l’Istituto per il Rilevamento Elettromagnetico dell’Ambiente (CNR-IREA) e l’Istituto Superiore per la Protezione e la Ricerca Ambientale (ISPRA), con la collaborazione di Eni e Total, realtà private ma anch’esse parte del Servizio nazionale della Protezione Civile, che hanno messo a disposizione i propri dati di sottosuolo. La finalità principale del progetto è stata ricostruire un quadro 3D di alta qualità della distribuzione dei diversi tipi di rocce nel sottosuolo in questa porzione di Appennino centralee delle possibili sorgenti sismogenetiche presenti in quel settore di crosta terrestre. Il progetto RETRACE-3D è stata un’occasione di lavoro multidisciplinare unica nel suo genere, alla quale hanno partecipato esperte ed esperti del Dipartimento della Protezione Civile e ricercatrici e ricercatori appartenenti ai Centri di Competenza del Dipartimento stesso, contribuendo al miglioramento delle conoscenze sui terremoti e ad una migliore valutazione della pericolosità sismica del territorio italiano. I percorsi di lavoro seguiti e le collaborazioni sviluppate all’interno del progetto sono da considerarsi di valore confrontabile con i risultati scientifici ottenuti, esi intende sottolineare come esperienze positive e propositive come quelle realizzate nel progetto RETRACE-3Dpossano costituire, in futuro, uno standard di azione e interazione tra i singoli ricercatori di diverse Istituzioni scientifiche e gli esperti del Dipartimento della Protezione Civile, anche al di fuori delle fasi emergenziali e post-emergenziali di una sequenza sismica. Il presente Rapporto finale è frutto dell’attività e dell’opinione degli autori. I contenuti non rappresentano necessariamente l’opinione generale delle istituzioni di cui i singoli autori fanno parte. La proprietà intellettuale dei risultati qui riportati è degli autori. Sebbene sia stato fatto ogni sforzo possibile per integrare i dati disponibili, non viene fornita alcuna garanzia, esplicita o implicita, in merito all'accuratezza e all'affidabilità dei dati forniti in RETRACE-3D GEOMOD. Gli utenti sono invitati a considerare l'incertezza epistemica intrinseca di tale prodotto per ogni suo possibile utilizzo e a tenere conto che il modello ha una scala equivalente a 1:250.000. RETRACE-3D GEOMOD è stato progettato per analisi a scala regionale; per studi e utilizzi diversi, a scale più locali (dettaglio superiore alla scala 1:250.000), andranno previste da parte degli utilizzatori indagini locali e sito specifiche. Gli utenti sono invitati a considerare attentamente la natura e la scala del contenuto di RETRACE-3D GEOMOD prima qualunque utilizzo. Gli autori di RETRACE-3D GEOMOD non sono responsabili per utilizzi diversi da quelli dichiarati.

Inundation maps are a fundamental tool for coastal risk management and in particular for designing evacuation maps and evacuation planning. These in turn are a necessary component of the tsunami warning systems’ last-mile. In Italy inundation maps are informed by a probabilistic tsunami hazard model. Based on a given level of acceptable risk, Italian authorities in charge for this task recommended to consider, as design hazard intensity, the average return period of 2500 years and the 84th percentile of the hazard model uncertainty. An available, regional-scale tsunami hazard model was used that covers the entire Italian coastline. Safety factors based on analysis of run-up variability and an empirical coastal dissipation law on a digital terrain model (DTM) were applied to convert the regional hazard into the design run-up and the corresponding evacuation maps with a GIS-based approach. Since the regional hazard cannot fully capture the local-scale variability, this simplified and conservative approach is considered a viable and feasible practice to inform local coastal risk management in the absence of high-resolution hazard models. The present work is a first attempt to quantify the uncertainty stemming from such procedure. We compare the GIS-based inundation maps informed by a regional model with those obtained from a local high-resolution hazard model. Two locations on the coast of eastern Sicily were considered, and the local hazard was addressed with the same seismic model as the regional one, but using a higher-resolution DTM and massive numerical inundation calculations with the GPU-based Tsunami-HySEA nonlinear shallow water code. This study shows that the GIS-based inundation maps used for planning deal conservatively with potential hazard underestimation at the local scale, stemming from typically unmodeled uncertainties in the numerical source and tsunami evolution models. The GIS-based maps used for planning fall within the estimated “error-bar” due to such uncertainties. The analysis also demonstrates the need to develop local assessments to serve very specific risk mitigation actions to reduce the uncertainty. More in general, the presented case-studies highlight the importance to explore ways of dealing with uncertainty hidden within the high-resolution numerical inundation models, e.g., related to the crude parameterization of the bottom friction, or the inaccuracy of the DTM.