Ercoli, Maurizio

A multidisciplinary approach including archaeological, geophysical, and geological/geomorphological surveys provided pieces of evidence that allowed us to identify the Sibari fault zone (SFZ) in Northern Calabria (Italy). The SFZ runs in a ~ NE-SW direction for a length of ~18 km from the Ionian coastline to Terranova da Sibari and has an oblique normal-dextral kinematics. The envelope of the SFZ is derived from several direct and indirect evidence resulting in subparallel and locally en-echelon fault traces over a maximum 500 m-wide band, running at different elevations across hills and flat lands. The SFZ was active since at least the Middle-Upper Pleistocene, producing faulting of alluvial deposits, marine terraces, drainage incisions, and the archaeological structures of Sybaris. Given the fault length and assuming a seismogenic behavior, the SFZ is a primary earthquake source possibly producing moderate to large earthquakes (M ≥ 6). We calculated the average slip rates along the SFZ based on the ages and on the accumulated displacements of offset streams and marine terraces. The estimates are of 0.05–0.18 mm/yr and 0.41–0.70 mm/yr for vertical and dextral slip, respectively. Based on both the measured (min. 30 cm) and the expected value (av. 40 cm) of lateral slip per event, we infer an average recurrence for surface faulting events on the SFZ of about 700–1000 yrs. The most recent surface faulting earthquake occurred on the fault is dated 1300–1100 yrs. ago, highlighting that the elapsed time approaches the estimated average recurrence. Considering these findings, the newly recognized SFZ should be included among the faults that contain a potential seismic hazard in this poorly known portion of the Ionian sector of northern Calabria.

The NE-dipping Anghiari normal fault, bounding to the west the Sansepolcro basin in the Upper Tiber Valley (northern Apennines), is thought to be a synthetic splay of the Altotiberina low-angle normal fault (LANF), an active ENE-dipping extensional detachment whose seismogenic behavior is debated. In order to assess the Anghiari fault capability to break the surface during strong earthquakes and be the source of historical earthquakes, we acquired high resolution topographic data, performed field survey and geophysical investigations (Seismic reflection, Ground Penetrating Radar, Electrical Resistivity Tomography) and dug three paleoseismological trenches across different fault sections of the Anghiari fault. The acquired data reveal for the first time the Late Pleistocene to historical activity of the Anghiari fault, constraining the age of seven paleo-earthquakes over the last 25 ka, the youngest of which is comparable with one of the poorly constrained historical earthquakes of the Sansepolcro basin. The yielded slip rate is >0.2 mm/yr averaged over the last 25 ka and the recurrence interval is about 2,500–3,200 years. An analysis of the anisotropy of the magnetic susceptibility performed in one of the paleoseismological trenches revealed an extensional stress field, continuously acting during the sedimentation of the entire trenched stratigraphy. Our results confirm the ability of the Anghiari fault to generate surface faulting earthquakes. In addition, if the Anghiari fault does sole at depth into the Altotiberina low-angle normal fault, this LANF could also be seismogenic and generate M > 6

In 2016–2017, a destructive sequence of earthquakes affected a wide portion of Central Italy, activating a complex, 80-km long system of SW-dipping normal faults and causing impressive surface faulting and widespread damage. Former studies providing reconstructions of the fault systems activated during this sequence, are mostly based on high-resolution seismological and geodetic data. In this paper, we integrate surface and subsurface geological data with the ones obtained by an irregular network of seismic reflection profiles, aimed at providing a comprehensive reconstruction of the subsurface lithologies and structures in this area. We have constructed a set of five geological cross-sections, passing through the mainshock epicentral areas (Mw > 5.5) of the seismic sequence. The cross-sections are extrapolated down to a depth of ca. 12 km, along which we have plotted relocated seismicity. Combined geological and seismological data support a new 3D seismotectonic model, illustrating the propagation through time and space of the seismic ruptures during the sequence. Our results show that the litho-mechanical stratigraphy exerted a primary control on the distribution of seismicity, as it is mostly hosted in the more competent lithologies (i.e. the Late Triassic-Paleogene succession, consisting of carbonates and evaporites). In addition, we illustrate the crucial role played by the inherited compressional structures in determining the lateral and vertical variations of the rheological properties of the upper crust and, eventually, the overall geometry and segmentation of the seismogenic extensional system. The workflow proposed here can be applied to other seismogenic zones throughout the world, since reliable seismotectonic models require an accurate reconstruction of the subsurface geological setting, based on a close integration of geological, geophysical and seismological data.

Central Italy was affected by a long seismic sequence in 2016 and 2017, characterized by five main-shocks with Mw>5.0. The Mw 6.5 mainshock occurred on 30 October 2016 close to the town of Norcia, located in the intra-Apennine Norcia basin. Different degrees of damages were observed during this seismic crisis, caused by a variable seismic shaking. This was also due to important 1D and 2D variation of Quaternary fluvio-lacustrine sediments infilling the basin. Following such considerations, a new geophysical dataset of seismic vibration measurements was acquired in the study area during the period April 2017-November 2019. We collected mainly single-seismic station noise data, to infer the distribution of resonance frequency (f0) of the basin. A total of 60 sites were measured to cover the entire extension in the basin. We deployed seismometers along three transects of a total length of 21 km, mostly along the main structural directions of the basin (i.e. NNW-SSE and NE-SW). Two 2D arrays of seismic stations with a elicoidal-shaped geometry, and a set of MASW active data were also acquired in the northern sector of the basin, in order to better constrain the seismic velocity of the sedimentary infilling. These new records have been integrated with available geological information in order to reconstruct the deep structure of the basin, as discussed in the research paper by [2]. The entire dataset used in [2] is here provided, together with 7 additional records recovered for the basin (i.e. N54-N60) and ancillary open-source geospatial data. The dataset can be used for different purposes: specific research on the Norcia basin, comparative studies on similar areas around the world, development of new data modeling and testing of new analysis software, and as a training dataset for machine learning applications.

During the 2016–2017, a seismic sequence struck the Central Italy, involving four regions (Umbria, Marche, Abruzzo and Lazio) and causing important damages and victims in inhabited areas such as Norcia and Amatrice towns. The strongest event of the seismic sequence was a Mw 6.5 event with epicenter at about 5 km far from the Norcia area, which is an intermontane basin prone to ground motion amplification. The historical town of Norcia and the surrounding hamlets were recently investigated by the microzonation activity, but information on the geometry and velocity are still partial considering the entire basin. Indeed, past studies aimed at reconstructing the elastic and geometrical properties focusing mainly on the northern part of the basin. Specifically in this paper, we integrated seismic and geological data to get a better knowledge of the properties of the Quaternary Norcia basin. A geological survey was carried out to provide a geological map and three geological cross-sections. We analyzed new seismic ambient vibrations data, collected by single-seismic stations, to infer the distribution of resonant frequency (f0) for the entire basin. We used passive arrays of seismic stations to better define the velocity profiles of the area. In the northern part of the basin, two 2D arrays with elliptical-like shapes were deployed showing strong discrepancies of the elastic soil properties in proximity of Norcia town. We found shear-wave velocities of the near-surface profile of about 300–400 and 500–800 m/s in presence of palustrine and alluvial fan deposits, respectively. Further, the values of f0 are abruptly varying from 0.5 Hz in the SW sector of Norcia village up to 2 Hz in its NE sector. Ambient vibration data reveal less pronounced variation of f0 in the southern part of the basin, with resonant values that are almost in the range 1–1.3 Hz. In the southern sector, a 1D array was arranged along a 5-km line and was analyzed by means of seismic noise cross-correlation analysis suggesting the presence of a deeper seismic contrast. The integration of geophysical and geological results has allowed to infer insights on the subsurface geometry of the basin.

During the 2016-2017, a long and complex seismic sequence struck the Central Italy, involving four regions (Umbria, Marche, Abruzzi and Lazio) and causing important damages and victims in inhabited areas such as Norcia and Amatrice towns. Norcia is an historical town situated in an extensional inter-montane basin, and a MCS intensity level of 7.5 was estimated after the 30 October 2016 Mw 6.5 event. In order to shed light on the subsurface geology and seismic response of the Norcia basin, we have performed an integrated geological and geophysical study, focusing our efforts on its most populated northern sector. The results of the field geological survey and the collection of available well stratigraphic logs have allowed us to identify the main Quaternary lithostratigraphic units laying on the carbonate substrate. From the bottom to the top we find: i) clayey deposits typical of lacustrine deposition, intercepted only by deep boreholes; ii) cemented conglomerates outcropping in the NE sector, related to wide alluvial fans occasionally affected by pervasive fracturing and faulting; iii) unconsolidated conglomerates units in silt and clay matrix typical of alluvial plain environment, mainly outcropping in the SW sector of the alluvial plane; iv) unconsolidated carbonate units representing debris-flow deposits filling the valleys that connect the carbonate slopes with the flat morphology of the plain; v) marshy and clayey deposit related to the actual palustrine deposits; After identified the main Quaternary geology units, we performed a geophysical survey with the well-known Horizontal-to-Vertical Spectral Ratio (HVSR/Nakamura) method. We deployed 20 single-seismic stations to record some hours of ambient vibrations. We used two different equipments (Reftek130 digitizer with Lennartz-5sec and a SARA Geobox 4.5 Hz) deployed along two main orthogonal transects (ENE-WSW and N-S direction, respectively) covering the whole area of interest. HVSR analysis shows and heterogeneous pattern of “fundamental frequency” (F0) according to the different portions of the basin. F0 is varying in the Norcia basin from 0.55 to 10 Hz. HVSR results can be summarized in four main groups, suggesting a direct link with the different characteristics of the lithostratigraphic units and their variable thickness: 1) a relatively flat spectrum with a single peak at high frequencies (range 4-10 Hz) for stations located above the carbonate bedrock; 2) broad peaks and F0 larger than 1 Hz in the NE area with respect to Norcia town. We observed broad peaks between 1-4 Hz and often a secondary peak at about 10 Hz, that is likely related to the presence of alluvial fan; 3) very narrow sharp peaks at 0.5-1 Hz are characteristic of the stations located in the SW-zone, which is the part where the basin shows higher thicknesses of the infilling continental deposits; 4) a bi-modal behaviour of the spectra, with a first broad peak between 0.5-1 Hz and a second one over 10 Hz is observed in the area of the inhabited city centre. The integration between the data provided by the geological survey, experimental geophysical H/V data and available information on the velocity allows us to infer the thicknesses of deposits underneath the basin, and the depth of the underlying carbonate bedrock. The integration of geological information and geophysical data, that show sharp lateral changes in the shape of peaks, suggest also a possible control of the main tectonic elements that characterize the area. Such new results, allowed us to carry out an integrated model of the substructure geometry of the Norcia basin. More specifically, the alluvial conoids present in the NE area seems to reach a depth variable from 20 to about 50 m, overlaying thick alluvial and lacustrine deposits throughout the basin. Below the Norcia inhabited area and in the SW part of the basin, which is the areas where the bedrock is suspected to be deeper, these “soft” deposits may reach a depth of 250-300 meters. The preliminary results of this study, also include some research products: an inedited digital geological map scale 1:10.000 created with QGIS software; a “Frequency-Amplitude” map from the HVSR analysis and two seismo-stratigraphic cross sections, highlighting the contact between infilling Quaternary units and the seismic "bedrock". Further acquisition of ambient vibrations trough 2D array of seismic stations will be carried out to better constrain the shear-wave velocity profile.

In this study, laboratory and GPR water content measurements on two sandy soils are compared. A robust procedure to constrain GPR surveys is provided, aiming to obtain accurate and reliable soil moisture information at the field scale. The application of the well-known Topp’s equation, provided good results only for water contents (hv) from 5 to 17%. Therefore, integrated analyses are mandatory to better understand the subsurface structures and the water content pattern in unsaturated zones. Data and results here presented represent the first reference for typical sandy soils outcropping in Central Italy, providing solid constraints for engineering and hydrogeological applications.

Starting from 24 August 2016, a long seismic sequence, including nine Mw > 5.0 earthquakes, struck a wide area of the Central Italy. A large amount of geological, geodetic, and seismological data envisages a complex system of NNW-SSE trending, seismogenic normal faults. These active tectonic structures are well known at the surface and consistent with previous seismotectonic studies. In order to improve the comprehension of the seismotectonic framework of this seismic sequence, we provide a novel reconstruction of the subsurface geology of the area close to the NorciaMw 6.5 mainshock (30 October 2016), based on previously unpublished seismic reflection profiles and available geological data. All the data have been synthesized along a 47 km long, WSW-ENE trending geological cross section, interpreted down to a depth of 12 km. Comparing the subsurface geological model with the available seismological data, we find that the majority of seismicity is confined within the sedimentary sequence and does not penetrate the underlying basement. The basement has been constrained at depths of 8 to 11 km and coincides with the cutoff of the seismicity. We have also traced the trajectories of the seismogenic normal faults activated during this seismic sequence, reconciling the high-angle (dip>65°) normal faults exposed at the surface, with their angle (dip < 50°) at hypocentral depths. The results of this study may be useful for better understanding the rheological properties of the seismogenic rock volume, as well as the coseismic deformations of the topographic surface observed by geodetic techniques and field mapping.

In this work, we analysed the seismic noise recorded at Mt. Etna by 18 stations during the interval 2007–2015 in the frequency band 0.1–0.3 Hz, chosen to avoid contamination from volcanic tremor. Variations in time of medium seismic velocity in the range − 0.8 to 0.8% were found, mostly affecting the stations located on the volcano summit and flanks. Based on the investigated frequency content, the Δv/v changes took place from the surface to a depth of ~ 4.5–6.5 km. To identify the source mechanism of the observed medium changes, the variations were quantitatively compared by wavelet transform coherence with volcano-tectonic and meteorological parameters. A significant relationship with meteorological parameters with seasonal periodicity (especially air temperature and snow loading) was found, probably caused by thermo-elastic strain and increasing-decreasing surface loading cycles. Moreover, a sharp medium velocity decrease, taking place in mid-December 2009 and clearly time-related to the largest volcano-tectonic strain release phenomenon of the investigated period, was also found. Such a velocity decrease was interpreted as resulting from ascent of fluids and gas exsolution taking place at the same time as the volcano-tectonic swarm.

The Castrovillari scarps (Cfs) are located in northern Calabria (Italy) and consist of three main WSW-dipping fault scarps resulting from multiple rupture events. At the surface, these scarps are defined by multiple breaks in slope. Despite its near-surface complexity, the faults likely merge to form a single normal fault at about 200 m depth, which we refer to as the Castrovillari fault. We present the results of a multidisciplinary and multiscale study at a selected site of the Cfs with the aim to (i) characterize the geometry at the surface and at depth and (ii) obtain constraints on the fault slip history. We investigate the site by merging data from quantitative geomorphological analyses, electrical resistivity and ground penetrating radar surveys, and palaeoseismological trenching along a ∼40 m high scarp. The closely spaced investigations allow us to reconstruct the shallow stratigraphy, define the fault locations, and measure the faulted stratigraphic offsets down to 20 m depth. Despite the varying resolutions, each of the adopted approaches suggests the presence of sub-parallel fault planes below the scarps at approximately the same location. The merged datasets permit the evaluation of the fault array (along strike for 220 m within a 370-m-wide zone). The main fault zone consists of two closely spaced NW–SE striking fault planes in the upper portion of the scarp slope and another fault at the scarp foot. The 3-D image of the fault surfaces shows west to southwest dipping planes with values between 70◦ and 80◦; the two closely spaced planes join at about 200 m below the surface. The 8-to-12-m-high upper fault, which shows the higher vertical displacements, accommodated most of the deformation during the Holocene. Results from the trenching analysis indicate a minimum slip per event of 0.6 m and a maximum short-term slip rate of 0.6 mm yr–1 for the Cf. The shallow subsurface imaging techniques are particularly helpful in evaluating the possible field uncertainties related to postfaulting modification by erosional/depositional/human processes, such as within stream valleys and urbanized zones.