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The RETRACE-3D project (centRal italy EarThquakes integRAted Crustal model) focused on the revision of all the available geological and geophysical data in the area interested by the 2016-2018 seismic sequence of central Italy, with the final aim to reconstruct a reliable and consistent 3D geological model of that area. It is based on a collaboration, which was framed into a formal agreement, between Dipartimento della Protezione Civile (the Italian Civil Protection Department), Istituto di Geologia Ambientale e Geoingegneria, and Istituto per il Rilevamento Elettromagnetico of the Consiglio Nazionale delle Ricerche, Istituto Nazionale di Geofisica e Vulcanologia, and Istituto Superiore per la Protezione e la Ricerca Ambientale. The agreement purpose was to develop a project aimed at the geological and seismotectonic characterisation of the crustal volume hosting that seismic sequence. We present and discuss the approach, methodology and results of the project. The 3D geological model of the study area is developed in detail down to a depth of about 12 km, and extended to the Moho based on available regional-scale information. The model is available on the RETRACE-3D project website (www.retrace3d.it).

Young and tectonically active mountain chains like the Central Apennines (Italy) represent challenging areas where to investigate the relationship between fault development and seismotectonics. Those areas are fashioned by a very complex patterns of seismicity, which have been associated both to single fault or complex fault systems activation. The high structural complexity and repeated cycles of tectonic phases can be clearly recognized even from surface geology, especially when supported by highly detailed stratigraphic constraints. Nevertheless, the overprint of subsequent deformational stages must be taken into careful account since geological observations made at the surface might mask different structural architecture at depth, with consequent important implication for seismotectonics. The RETRACE-3D project focused on the review of a large set of underground data acquired for hydrocarbons explorations in the area struck by the 2016-2018 Central Apennines seismic sequence, integrated with surface geological information, to build a robust and comprehensive 3D geological model to be related to observed seismicity. Results primarily show that, at least for the shallow crust, the general architecture of the chain is still dominated by large-scale compressional structures associated to the build-up phase of the Central Apennines. We generally found widespread evidence of fault segmentation, reactivation of faults, as well as the recent generation of new sets of extensional faults. For these latter in particular, the surface expression and their evolution are conditioned by the presence of previous structures at depth. This contribution would open new points of discussion regarding a more realistic estimate of seismic hazard of complex areas such as the Central Apennines.

Young and tectonically active mountain chains like Central Apennines (Italy), characterized by a high structural complexity, represent astonishing examples for making strong inferences on seismotectonics. Repeated cycles of tectonic phases recognized by surface geology result in the development of a series of interacting fault systems as well as in a widespread reactivation of inherited structures, usually disarticulating pre-existing tectonic arrangements. In this context, what is observable at surface might mask a different structural architecture at depth, where shallow structures may be decoupled from the deeper ones. In the last decades, Central Apennines have been affected by a complex pattern of seismicity, which has been associated to the activation of both single faults and complex fault systems. Within the framework of the RETRACE-3D project, we reviewed a large set of underground data acquired for hydrocarbons explorations in the area struck by the 2016-2018 Central Apennines seismic sequence. Main goal is to build a comprehensive 3D geological model able to match the superficial observations with the deeper ones, and with the recent seismicity. Although the current extensional tectonic regime, results primarily show that the main architecture of this portion of the chain is still dominated by previous compressional large-scale structures, widespread evidence of segmentation, reactivation and even inversion of various sets of inherited faults. A reliable 3D geological modelling down to seismogenic depths as well as the recognition of reactivated paleo-structures play a fundamental role in understanding the seismotectonics of the considered area, also allowing to more robustly infer on the seismogenic potential of faults. This work would also open new points of discussion regarding information and input data needed to improve the assessment of seismic hazard in mountain chains such as the Central Apennines.

The structural architecture of a portion of the eastern side of the Tyrrhenian Sea back-arc basin has been defined reinterpreting a public data set made up by seismic reflection profiles. A detailed reconstruction of the extensional front migration trough time across the area has been achieved. Migration has been defined by identifying the generation of unconformities in the graben-like basins developed in the area, as due to the activation and deactivation of normal faults. Such phenomena are part of a tectonic process that also involved blocks rotation, crustal thinning, and stretching. Syn-rift extension affected the area since the early to middle Miocene (our estimate), principally interesting the north-westernmost sectors. During late Miocene and throughout the Plio-Quaternary the extensional front moved stepwise toward the southeastern and eastern sectors. Widespread postrift conditions established over the whole area since the late Pliocene to early Pleistocene. Since the Quaternary, the locus of active extension further migrated toward the present onshore area, where a pronounced volcanic phase developed. In this evolutionary framework the rates of observed migration could be correlated with the acceleration of Calabrian slab rollback since Pliocene. Furthermore, direct evidences of magmatism were not recognized in the offshore. Although the observed crustal thinning, the absence of volcanic bodies in the study area could be related to normal faults which were unable to sufficiently extend the crust, in association with lower crust and mantle processes unable to produce melts.

The structural architecture of a portion of the eastern side of the Tyrrhenian Sea back-arc basin has been defined reinterpreting a public dataset made up by seismic reflection profiles. A detailed reconstruction of the extensional front migration trough time across the area has been achieved. Migration has been defined by identifying the generation of unconformities in the graben-like basins developed in the area, as due to the activation and deactivation of normal faults. Such phenomena are part of a tectonic process that also involved blocks rotation, crustal thinning and stretching. Syn-rift extension affected the area since the ?Early-Middle Miocene, principally interesting the north-westernmost sectors. During late Miocene and throughout the Plio-Quaternary the extensional front moved stepwise toward the southeastern and eastern sectors. Widespread post-rift conditions established over the whole area since the late Pliocene-early Pleistocene. Since the Quaternary the locus of active extension further migrated toward the present onshore area, where a pronounced volcanic phase developed. In this evolutionary framework the rates of observed migration could be correlated with the acceleration of calabrian slab roll-back since Pliocene. Furthermore direct evidences of magmatism were not recognized in the offshore. Although the observed crustal thinning, the absence of volcanic bodies in the study area could be related to normal faults which were unable to sufficiently extend the crust, in association with lower crust and mantle processes unable to produce melts.

We compute a high-resolution topographic model of the Moho beneath the fault system activated during the 2016–2017 Central Italy seismic sequence, using Receiver Function (RF) analyses. We document that Ps conversions recorded in RF data-set varies abruptly at very short distance across the crustal lineament called Ancona-Anzio Line (AAL). Moho depth varies from about 25-30 km in the Tyrrhenian domain on the West to 35-40 km in the Adriatic domain in the East. Where the two domains are juxtaposed along the AAL, Moho depth values cluster around 50 km depth, in a stripe-like area 20 km wide. Such unique feature marks the deformation zone in the lithosphere and testifies the abrupt change in delamination style in the two sectors of the Apennines. Intermittent large normal faulting earthquakes driven by across-belt extension break through such inherited strong structural changes, conditioned by localized barriers to fluids migration and overpressuring.

Despite the exponential increase of studies on plastic debris in recent years, there are still few works focusing on the problem as it relates to inland waters: little is known about the accumulation and dispersion dynamics on lake shores, and there are no standardized sampling methods for monitoring purposes. The accumulation of plastic litter in natural habitats also threatens the resident organisms. In this paper, we investigated the abundance and accumulation of plastic particles, ranging in size from 1 to 50mm, from the beach sediment of three volcanic lakes in Central Italy: Albano, Bracciano, and Vico. The collection was designed to define the most important variables that one must consider in order to obtain a representative sample of plastic litter in a lake environment. In view of the high heterogeneity of sampling protocols used, comparison among the obtained results is limited and sometimes impossible. By using one of the proposed sampling methodologies, and critically analyzing the results, we aimed to highlight a possible monitoring criterion and to identify specific elements that can be meaningful and representative. The samples were collected in May and September 2017. For each lake, we sampled plastic items and sediments from two beaches. Albano contained the largest amount of plastic (in weight), while Bracciano had the largest number of particles. Our observations lead us to infer that the number of particles is the parameter most sensitive to environmental variations, as well as the more suitable for monitoring with greater definition the differences between sites. Moreover, sampling should be taken in different seasons, following a sampling pattern that includes at least two beaches placed in strategic positions with respect to wind and waves. In order to identify new indicators to evaluate the entry points of plastic into the food web, we collected, from the same sites analyzed, some specimens of the Talitrid Amphipod Cryptorchestia garbinii, a detritivorous species having a critical role in debris turnover of these environments. To investigate the microplastic (MP) ingestion in natural conditions, we analyzed their digestive tracts with both Nile red staining method and micro-FTIR spectroscopy. The analyses confirmed that C. garbinii was able to ingest plastics in natural conditions. Therefore, it can signify one of the entry points for microplastics (MPs) in the trophic chain. This observation constitutes the first evidence of MP ingestion in this species.

We describe the eruptive activity of the Pleistocene composite Baccano maar crater in the Sabatini Volcanic Complex (Central Italy) combining stratigraphy, grain size/componentry and rare earth element and Yttrium (REY) composition of its eruptive products with the stratigraphy and geothermal data derived from deep wells drilled on the Baccano structural high. The main lithological characteristics of the basal Baccano maar pyroclastic deposit, composed of more than 60% wt of non-thermometamorphosed lithic clasts from the sedimentary basement, show that the first eruption was magmatic-hydrothermal in nature. The lithology of the sedimentary lithic clasts indicates that the fragmentation level was at a depth of −1,000 to −1,200 m, with fragment depth verified by deep well stratigraphy. The 15% wt juvenile non-vesicular glass components suggest that magma played a minor role in powering the eruption. Assuming that the high-salinity hot hydrothermal fluids (365−1,400 m) by the aggressive hydrothermal fluids enriched in acid components (HF, HCl, and H2SO4) may have contributed to increased CO2 partial pressure that helped to drive the hydrofracturing. This could have caused rapid vapour separation and pressure drop, allowing the almost simultaneous breaking of the aquifer cover and brecciation of the calcareous units down to −1,000 to −1,200 m depth. The relative abundance of calcareous lithics in the basal part of the first Baccano eruptive unit, representing about the upper 200 m of stratigraphy below the top of the Baccano structural high, reveals the descent of the piezometric surface during the eruption. Combining deep well information and maar product stratigraphy, using also REY data from maar pyroclastic fragments and the basement rocks we draw an interpretative model for the Baccano maarforming eruption, concluding that a) magmatic-hydrothermal eruptions may originate deeper than previously thought, and b) hydrothermal fluids circulating in limestone aquifers ma