We present the first version of the software POPE (Probability of Occurrence of Paleoseismic Earthquakes, POPEv1.0), designed to assist seismologists in reconstructing the timing of paleoseismic earthquakes on a fault, based on event ages derived from multiple trenches along that fault. The main feature of POPEv1.0 is that it accounts for uncertainties in the input paleoseismic data (i.e. the paleoearthquake ages from trenches) and generates multiple fault rupture scenarios by applying a probabilistic aggregation method that also considers less likely, but plausible, ways of combining paleoseismological data from different trenches. Some of these scenarios may subsequently be excluded through an independent expert selection process, based on their consistency with available stratigraphic, structural and historical constraints. To show the use of POPEv1.0 and discuss the underlying methodology, we apply it to the paleoseismic data from two faults in Central Italy, the Ovindoli-Pezza and Monte Ocre faults, and discuss the implications of results for seismic hazard assessment in the region.

The 2020 Mw 6.4 Petrinja earthquake in central Croatia is one of the European strongest continental earthquakes in recent decades. This event shed light on the poorly investigated Petrinja-Pokupsko Fault (PPKF) zone, a right-lateral fault system accommodating a fraction of the shortening between the Adria and European plates. Through field observations and high-resolution Lidar-derived digital elevation models of the central section of the PPKF, we precisely mapped the fault trace, revealing a discontinuous geometry with a main fault strand and left-stepping segments in agreement with the position of the 2020 surface ruptures. To the north, the accumulated relief from this transpressive fault system decreases, and the fault trace becomes less distinct, suggesting a northward propagation of the deformation. Cumulative offsets of 4 to 24 meters along the main fault strands in the central and southern sections of the fault attest to its Quaternary activity. Dating results suggest offset markers at the Marine Isotopic Stage 4 (MIS 4), the Late Glacial Maximum (LGM) or the Early Holocene periods, allowing for the first direct estimation of the fault slip rates. Preliminary estimates indicate that, assuming a common MIS 4 or LGM age for the investigated markers, fault slip rates range from 0.2 to 0.7 mm/yr and 0.7 to 1.6 mm/yr, respectively. In contrast, assigning Early Holocene ages would imply much higher - and likely unrealistic - slip rates of 1.6 to 3.9 mm/yr. Although the estimated loading rates vary greatly and depend on strong assumptions regarding the age of the markers abandonment, our results suggest a minimum fault slip-rate of 0.2 mm/yr for local seismic hazard assessments.

The 2020 MW 6.4 Petrinja (Croatia) earthquake induced extensive and diversified liquefaction and lateral spreading phenomena within approximate to 20 km radius from the epicenter. A detailed investigation from field and Unmanned Aerial Vehicle (UAV) surveys was carried out by a European researcher team (EUTeam) in the months following the mainshock. This work focuses on 61 surveyed sites: field observations were coupled with laboratory tests for soil classification and sediment composition. The adopted procedure provides an in-depth geological and geotechnical characterization of the liquefied sites in the Petrinja region. The liquefaction evidences are mainly associated to alluvial plain environments, in particular to meander paleochannels, and the ejected material is predominantly siliciclastic, made up of very rounded quartz-rich lithics. Few sites are dominated by angular carbonate rock fragments, related to liquefaction in cataclastic deposits along tectonic fractures. The ejected sediment includes a wide range of grain-size from silt to gravel. The peculiar presence of gravel in the liquefied deposits (up to 28% in some samples) confirms the need of expanding the grain-size boundaries for liquefiable coarse-grained gravelly soils. The information gathered from the post-earthquake surveys and from the sedimentological and geotechnical analysis for each studied site were compiled in organized data sheets, providing a striking instrument for in-depth earthquake studies, both for geological and geotechnical engineering purposes. The format defined for the data sheet can be functional and applicable also in liquefaction studies from different geological and depositional settings.

Using the published paleoseismological trenching data for 16 faults in Central Italy, we compile a new data base of surface faulting earthquakes, having a quite stationary temporal distribution since 6000 BCE. By applying a probabilistic aggregation method, we correlate the event ages from distinct trenches on each fault, to construct all possible individual fault rupture scenarios, consistent with geological constraints. These inferred fault time histories are the basis for both individual fault and regional seismic hazard evaluation. We found that the mean recurrence time of each fault goes from about 1 to 4 thousand years for individual faults, whereas the value at regional scale is close to 120 yr. The small size of individual fault data samples does not allow us to infer straightforward information on the fault temporal behaviour, but only to evaluate the reliability of a chosen occurrence model for each fault. Therefore, hazard assessment is carried out by including the uncertainties related to both ages and probability distribution of the interevent times. We find that both these have a large impact on the probabilities of next rupture for individual faults: these depend on basic features of the temporal model and on the relation between the elapsed time and the mean interevent time. At a regional scale, we cannot exclude the simplest possible model, that is, the Poissonian behaviour, that provides quite stable probabilities of future events, close to 27 per cent in the next 50 yr.

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.

Europe has experienced over the last years earthquakes of moderate magnitude (Mw 5-6), yet destructive, reminding us of the seismogenic potential of slowly deforming regions. Among them, the 2020 Mw 6.4 Petrinja earthquake ruptured the Petrinja-Pokupsko Fault (PPKF) in Central Croatia, about 50-km southeast of Zagreb, a region in which the caracterisation of seismogenic faults had been insufficiently studied before that event. Understanding the strain accommodation through time and space is critical for accurate assessment of the regional seismic hazard.Using field observations and high-resolution topographical data derived from airborne LiDAR (~10 cm resolution) and tri-stereo satellite images (Pléiades, resolution 50 cm), we accurately mapped the fault trace, underlined at several sites by geomorphic markers such as valleys, terrace risers, and alluvial fans that have recorded cumulative displacements ranging from 5 to > 50 m and potentially up to ~180 m. Along the studied section, our fault mapping is composed of a clear NW-SE-trending 10-km-long strand between Donja and Cepelis, and of 1-4-km-long right-stepping segments marked by a non-negligible vertical component. The southern strand is composed of 2-3 sub-parallel segments that accommodate the deformation within a < 500 m wide fault zone.We have identified several sites on the main southern strand where offsets have been accurately measured and where displaced markers have been sampled for cosmogenic nuclide exposure dating and radiocarbon datings. This will allow to estimate the slip-rate for this fault at different sites and over several time spans.The mapped fault appears very discontinuous with the deformation absorbed by a series of small fault sections rather than on a single fault strand. This likely reflects a recent transpressive deformation, with immature faults, in agreement with the source parameter of the 2020 Petrinja earthquake derived from seismology.Finaly, the 2020 coseismic surface ruptures affected the northern section of the PPKF, while the mapped cumulative displacements appears more prominent along the southern section. A better knowledge of the seismic history of this entire fault system is thus crucial for seismic hazard assessment of this area.

The Val d’Agri (VA) oilfield in the Lucanian Apennines (southern Italy), represents the largest onshore in Europe. Since the 1990's, hydrocarbons are produced from a fractured carbonate reservoir with an average extraction rate of 7*104 barrels/day of oil and 3*106 Smc/day of gas. Part of the wastewater has been re-injected since 2006 into a marginal portion of the reservoir by a high-rate well (Costa Molina 2, CM2). Charged by the Italian oil and gas safety authority, the National Institute of Geophysics and Volcanology (INGV) monitors the VA industrial hydrocarbon operations through the research activity of a dedicated working group (CMS, Centro di Monitoraggio del Sottosuolo) and according to the governmental monitoring guidelines. The CMS operates the real-time acquisition and offline analyses of seismic data recorded at 56 seismic stations associated with public and private local seismic networks. The principal aim of the CMS is to investigate the risk associated with industrial activities that can induce or trigger seismic events by producing stress changes within the upper crustal volume. Previous works have highlighted a spatio-temporal relationship between micro-seismicity (ML ≤ 2.2) and wastewater injection, delineating a NE-dipping back-thrust near the CM2. Part of the microseismicity recorded in the southwestern portion of the VA has also been associated with the water level changes of the Pertusillo lake. One of the main challenges is to define an accurate structural setting of the VA to understand the potential of earthquakes in the area and investigate the presence of active faults. The VA consists of a Quaternary extensional tectonic basin and it is one of the areas of highest seismic hazard in Italy (Basilicata, 1857, M7 earthquake). The basin is bounded by two parallel and oppositely dipping normal fault systems: the Monti della Maddalena Fault System (MMFS) on its western side and the Eastern Agri Fault System (EAFS) on the eastern one. The characterization of the ongoing tectonic activity of the MMFS and EAFS, and their hierarchical relationship is still generating debate among the scientific community. We adopt a multidisciplinary approach based on detailed geological-structural, geophysical and seismic analyses, and electrical resistivity tomography, aimed at reconstructing the subsurface geology of the area and recognizing and characterizing the active and capable faults, and the associated potential for local seismic hazard. We present and discuss the results of this work, focusing on the relative location of seismic events that occurred between March and June 2022. The outcomes allow inferring interesting geologic constraints, highlighting the relationships between the distribution of local seismicity and the structural setting of the area in the uppermost crust (depth < 6 km).

SUMMARYOn 29 December 2020, a shallow earthquake of magnitude Mw 6.4 struck northern Croatia, near the town of Petrinja, more than 24 hr after a strong foreshock (ML 5). We formed a reconnaissance team of European geologists and engineers, from Croatia, Slovenia, France, Italy and Greece, rapidly deployed in the field to map the evidence of coseismic environmental effects. In the epicentral area, we recognized surface deformation, such as tectonic breaks along the earthquake source at the surface, liquefaction features (scattered in the fluvial plains of Kupa, Glina and Sava rivers), and slope failures, both caused by strong motion. Thanks to this concerted, collective and meticulous work, we were able to document and map a clear and unambiguous coseismic surface rupture associated with the main shock. The surface rupture appears discontinuous, consisting of multi-kilometre en échelon right stepping sections, along a NW–SE striking fault that we call the Petrinja-Pokupsko Fault. The observed deformation features, in terms of kinematics and trace alignments, are consistent with slip on a right lateral fault, in agreement with the focal solution of the main shock. We found mole tracks, displacement on faults affecting natural features (e.g. drainage channels), scarplets and more frequently breaks of anthropogenic markers (roads, fences). The surface rupture is observed over a length of ∼13 km from end-to-end, with a maximum displacement of 38 cm, and an average displacement of ∼10 cm. Moreover, the liquefaction extends over an area of nearly 600 km2 around the epicentre. Typology of liquefaction features include sand blows, lateral spreading phenomenon along the road and river embankments, as well as sand ejecta of different grain size and matrix. Development of large and long fissures along the fluvial landforms, current or ancient, with massive ejections of sediments is pervasive. These features are sometimes accompanied by small horizontal displacements. Finally, the environmental effects of the earthquake appear to be reasonably consistent with the usual scaling relationships, in particular the surface faulting. This rupture of the ground occurred on or near traces of a fault that shows clear evidence of Quaternary activity. Further and detailed studies will be carried out to characterize this source and related faults in terms of future large earthquakes potential, for their integration into seismic hazard models.

At Mt. Etna (Italy), volcano‐tectonic earthquakes produce impressive surface faulting despite their moderate magnitude ( M < 5.5), with historically well‐documented ruptures featuring end‐to‐end lengths up to 6–7 km. The 26 December 2018, M w 5.0 earthquake represents the strongest event of the last 70 years, with ground ruptures extending for 7.5 km along the Fiandaca fault, a partially hidden structure in the volcano's eastern flank. Field data collected by the EMERGEO Working Group (INGV) are here integrated with high‐resolution photogrammetric surveys and geological‐morphological observations to enable a detailed structural analysis and to reconstruct the morphotectonic process of fault growth. The deformation zone develops in a transtensional regime and shows a complex pattern, consisting of brittle structures arranged in en‐échelon scale‐invariant overlapping systems. Offsets and kinematics vary along the strike due to a major bend in the fault trace. We reconstructed a prevailing right‐lateral displacement in the northern section of the fault and a dextral oblique slip in the southern one (max 35 cm); the dip‐slip component increases southward (max 50 cm) and overall resembles the along‐strike pattern of the long‐term morphological throw. The kinematic analysis indicates a quasi‐rigid behavior of the two fault blocks and suggests a geological model of rupture propagation that explains both the location of the seismic asperity in the northern section of the Fiandaca fault and the unclamping in the southern one. These findings are used to propose a conceptual model of the fault, representing insights for local fault‐based seismic hazard assessment.

Earthquakes and related coseismic effects at the surface, both primary and secondary, such as liquefaction and lateral spreading, can impact humans due to induced economic or social disruptions (e.g. slope, bridge and building foundation failures, flotation of buried structures). In this respect, it results of primary interest to map liquefaction induced evidences soon after an earthquake. On the 29th December 2020, a major earthquake (Mw 6.4) occurred in Croatia, close to Petrinja, 45 km south of Zagreb, generating widespread liquefaction and lateral spreading phenomena in a radius of approximately 20 km from the epicentre. A European team of researchers (geologists and engineers), in strict collaboration with the Croatian Geological Survey, performed field reconnaissance campaigns with the aim to provide a detailed identification and characterization of the primary and secondary geological and geotechnical coseismic effects induced by the Croatian earthquakes. Specifically with reference to the liquefaction phenomena, the Working Group integrated the data collected directly in the field with those from remote survey by drone aerial photos acquired in the post-event immediate. The adopted process allowed the collection of the liquefaction record with the highest possible completeness both in terms of pattern and distribution of the phenomena. The database includes several detailed case studies typified by the following characteristics: (1) liquefaction occurring on alluvial plain sites (Kupa river, Sava river and Glina river); (2) blows made by sand and/or gravel with local presence of shells and armored mud balls; (3) lateral spreading phenomena along road and river embankments; (4) sand ejecta of different grain size and matrix, even at the same site; (5) sand and/or gravel ejecta along fault traces. The characteristics of these features are discussed with reference to the alluvial setting and tectonic context. All together, the detailed survey of these recent liquefaction features will assist to build new empirical relations, to update the existing ones and to mitigate the effects of future earthquakes recognizing liquefaction prone areas for a correct land use planning, as for seismic microzonation studies.

The 29 December 2020, Mw 6.4 Petrinja earthquake nucleated at a depth of ~10 km in the Sisak-Moslavina County in northern Croatia, ~6 km WSW of the Petrinja town. Focal mechanisms, aftershocks distribution, and preliminary Sentinel-1 InSAR interferogram suggest that the NW-SE right-lateral strike-slip Pokupsko-Petrinja fault was the source of this event. The Croatian Geological Survey, joined by a European team of earthquake geologists from France, Slovenia and Italy, performed a prompt systematic survey of the area to map the surface effects of the earthquake. The field survey was guided by geological maps, preliminary morphotectonic mapping based on 1:5,000 topographical maps and InSAR interferogram. Locally, field mapping was aided by drone survey. We mapped unambiguous evidence of surface faulting at several sites between Župić to the NW and Hrastovica to the SE, in the central part of the Pokupsko-Petrinja fault, for a total length of ~6.5 km. This is probably a minimum length since several portions of the fault have not been explored yet, and in part crossing forbidden uncleared minefields. Surface faulting was observed on anthropic features (roads, walls) and on Quaternary sediments (soft colluvium and alluvium) and Miocene bedrock (calcarenites). The observed ruptures strike mostly NW-SE, with evidences of strike-slip right-lateral displacement and zones of extension (opening) or contraction (small pressure ridges, moletracks) at local bends of the rupture trace. Those ruptures are interpreted as evidences of coseismic surface faulting (primary effects) as they affect the morphology independently from the slope direction. Ground failures due to gravitational sliding and liquefaction occurrences were also observed, mapped and interpreted as secondary effects (see Amoroso et al., and Vukovski et al., this session). SE of Križ, the rupture broke a water pipeline with a right-lateral offset of several centimetres. Measured right-lateral net displacement varies from a few centimetres up to ~35 cm. A portion of the maximum measured displacement could be due to afterlisp, as it was mapped several days after the main shock. Hybrid surface ruptures (shear plus opening and liquefaction), striking SW-NE, with cm-size left-lateral strike-slip offsets were mapped on the northern side of the Petrinja town, ~3 km NE of the main fault. Overall, the rupture zone appears discontinuous. Several factors might be inferred to explain this pattern such as incomplete mapping of the rupture, inherited structural discontinuities within the Pokupsko-Petrinja fault system, or specific mechanical properties of the Neogene-Quaternary strata

This paper provides a new contribution to the construction of the complex and fragmentary mosaic of the Late Holocene earthquakes history of the İznik segment of the central strand of the North Anatolian Fault (CNAF) in Turkey. The CNAF clearly displays lower dextral slip rates with respect to the northern strand however, surface rupturing and large damaging earthquakes (M > 7) occurred in the past, leaving clear signatures in the built and natural environments. The association of these historical events to specific earthquake sources (e.g., Gemlik, İznik, or Geyve fault segments) is still a matter of debate. We excavated two trenches across the İznik fault trace near Mustafali, a village about 10 km WSW of İznik where the morphological fault scarp was visible although modified by agricultural activities. Radiocarbon and TL dating on samples collected from the trenches show that the displaced deposits are very recent and span the past 2 millennia at most. Evidence for four surface faulting events was found in the Mustafali trenches. The integration of these results with historical data and previous paleoseismological data yields an updated Late Holocene history of surface-rupturing earthquakes along the İznik Fault in 1855, 740 (715), 362, and 121 CE. Evidence for the large M7 + historical earthquake dated 1419 CE generally attributed to this fault, was not found at any trench site along the İznik fault nor in the subaqueous record. This unfit between paleoseismological, stratigraphic, and historical data highlights one more time the urge for extensive paleoseismological trenching and offshore campaigns because of the high potential to solve the uncertainties on the seismogenic history (age, earthquake location, extent of the rupture and size) of this portion of NAFZ and especially on the attribution of historical earthquakes to the causative fault.

After the 2004 Indian Ocean (IOT) and the 2011 Tohoku-oki tsunamis, new research in tsunami-related fields was strongly stimulated worldwide and also in the Mediterranean. This research growth yields substantial advancements in tsunami knowledge. Among these advancements is the ?Paleotsunami? research that has marked particular progress on the reconstruction of the tsunami history of a region. As an integration of the historical documentation available in the Mediterranean and the Gulf of Cadiz areas, geological and geoarchaeological records provide the insights to define the occurrence, characteristics, and impact of tsunamis of the past. Here, we present the recent advancements done for both the onshore and offshore realms. As for the onshore, we discuss case studies dealing with recent high-resolution works based on: a) direct push in situ sensing techniques, applied to identification and characterization of typical paleotsunami deposits features; b) combined XRF-X-CT approach, implemented for the identification of fine-scale sedimentary structures useful for the definition of the causative flow dynamics; c) the geoarchaeological ?new field? contribution, with the development of specific diagnostic criteria in search for tsunami impact traces in archaeological strata; d) comparison of multiple dating methods and of different modeling codes for the definition of the potential source for the displacement of boulders of exceptional dimension, identified by 3D size calculation. As for the offshore advancements, we present case studies focusing on the recognition of tsunami deposits and their sedimentary traces in the geological record from the nearshore, thanks to diver-operated coring equipment, down to the continental slope, by means of vibracorer and long gravity core sampling in deeper areas. The examples provided show a multiproxy approach with a high potential of retrieving a complete record of paleotsunami traces at least during the Holocene. This is based on the combination of multidisciplinary approaches including X-ray imaging, high-resolution measurement of physical properties, X-ray fluorescence data, grain-size analysis, micropaleontology, palynological content, isotopic and optically stimulated luminescence dating methods.

Among the geologic data, trenching records of paleoearthquakes represent an important input for the development of seismic hazard evaluations and, specifically, for the characterization of fault rupture behavior in time. Based on the available paleoseismological trenching data in the Central Apennines (Italy) we have compiled a new database of surface faulting earthquakes for 10 faults. The compilation contains 109 surface faulting events, occurred in the past similar to 28 kyr. Events younger than 7 kyr (59 dated events) are much better constrained and, therefore, are the basis for most of the analyses. Through a quantitative multistep method, we integrate paleoseismic trench data and treat them statistically, providing relevant improvement needed for trenching-based seismic hazard evaluation. Indeed, the combined analysis of trenching data from multiple sites on the same fault led to a reduction of the approximations and uncertainties in the rupture history of individual faults. The procedure was also applied on specific fault systems and indicated that the single faults may have occasionally ruptured simultaneously, or close in time, in the past. The whole set of age ranges was also statistically analyzed to produce regional earthquake scenarios for a period much longer than the millennial historical record. The built scenarios for the last 7 kyr define a regional mean inter event time (IET) of 230-240 yr, comparable with the average recurrence time of about 200 yr calculated for the region. We also identify the possible occurrence of earthquake storms, i.e., concentration of surface faulting earthquakes in the region within time periods of 200 yr, suggesting a variability in time of the seismic behavior of the faults, with alternation of peaks of activity with more "quiet" periods. Even though the paleoseismic data from the Apennines contains uncertainties, the results appear quite stable and promising for future applications in earthquake-hazard assessment.

We provide the first 3‐D resistivity image of the Pian Grande di Castelluccio basin, the main Quaternary depocenter in the hangingwall of the Mt.Vettore–Mt. Bove normal fault system (VBFS), responsible for the October 30, 2016 M w 6.5 Norcia earthquake (central Italy). The subsurface structure of the basin is poorly known, and its relation with the VBFS remains debated. Using the recent Fullwaver technology, we carried out a high‐resolution 2‐D transect crossing the 2016 coseismic ruptures coupled with an extensive 3‐D survey with the aim of: (a) mapping the subsurface of the basin‐bounding splays of the VBFS and the downdip extent of intrabasin faults; (b) imaging the infill and pre‐Quaternary substratum down to ∼1 km depth. The 2‐D resistivity section highlights under the coseismic ruptures a main dip‐slip fault zone with conjugated splays. The 3‐D resistivity model suggests that the basin consists of two depocenters (∼300 and ∼600 m deep, respectively) filled with silty sands and gravels (resistivity <300 Ωm), bounded and cross‐cut by NNE‐, WNW‐, and NNW‐trending faults with throws of ∼200–400 m. We hypothesize that the NNE‐trending system acted during the early basin development, followed by NNW‐trending and currently active splays of the VBFS that overprint pre‐existing structures and locally control the infill architecture. Moreover, beneath the basin we detect a shallow NW‐dipping blind fault. The latter is likely a hangingwall splay of the adjacent regional Mts. Sibillini Thrust, which may have been partly involved in the rupture process of the Norcia mainshock.

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.

The Vettore–Bove normal fault system in central Italy ruptured during the 2016 M W 6.5 Norcia earthquake causing extensive surface faulting. At the Pian Grande di Castelluccio hanging wall basin, along the southern section of the fault ruptured during the M W 6.5 mainshock, we performed a high‐resolution seismic reflection/refraction experiment aimed at (a) imaging the shallow pattern of the fault system, and (b) reconstructing the architecture of the continental infill. We collected three profiles for a total length of ∼8 km. We used a reflection processing flow and non‐linear refraction tomography to obtain migrated stack sections and P‐wave velocity images resolved down to the depth of the pre‐Quaternary substratum. The main profile in the northern part of the basin crosses the westernmost splays of the ruptured fault zone striking N150°–170°. Seismic imaging unravels a ∼1 km‐wide fault zone comprising three W‐throwing splays and subsidiary faults, which affect the continental infill and produce a minimum aggregate Quaternary throw of ∼400 ± 100 m. Recent deformation is localized in this part of the surveyed fault section, attesting active displacement accumulation of the Vettore–Bove fault system. The other profiles in the central‐southern part of the basin show additional faults, likely striking N20°–40° and which concurred to generate a ∼500 m‐deep depocenter. These faults were mostly active during an early extensional phase; however, one of them likely displaces shallow layers with a throw close to the resolution limit of seismic data (<10 m), suggesting activity in the Late Pleistocene.

We investigated the late Quaternary throw distribution of the main normal fault that ruptured during the Mw 6.5 2016 earthquake in central Italy by means of a high-resolution structure-from-motion (SfM)-derived Digital Surface Model (DSM). We focused on a key area along the Cordone del Vettore fault (CDV), which is part of the Vettore-Bove fault system (VBFS). The CDV displays a prominent compound post-glacial scarp that allowed the reconstruction of the along-strike cumulative throw distribution. We propose a geometric approach to calculate the CDV fault throw distribution from the reconstruction of a displaced glaciation-related erosional surface, used as a geomorphic marker, and a series of closely spaced cross profiles. The proposed calculation accounts for both the slip vector direction and the degraded scarp top, including field data on fault dip angles. Following this approach, we recognized two scarps with a minimum average fault throw of similar to 21 m and similar to 35 m for this section of the investigated fault strand. The correlation with the possible post-LGM (Last Glacial Maximum) deglaciation phases of the erosional surface suggests a minimum scarp age of 25-27 ka cal BP. Such an age provides a reasonable CDV fault throw rate of similar to 0.8 mm/a, comparable with known long-term throw rates of the VBFS and active Apennines normal faults. By comparing the reconstructed long-term Cordone del Vettore throw distribution with the 2016 coseismic one, similar to 24 2016-like surface faulting events are required to generate the main cumulative scarp, under the assumption of constant slip per event. This, along with the age of the scarp, yields an average earthquake recurrence time interval of similar to 1100 a. These results suggest the presence of multiple regional markers that correlates with different LGM (if not pre-LGM) major glacial phases, whose erosional processes allow the preservation of pre-existing bedrock fault scarp remnants. (C) 2021 The Authors. Published by Elsevier B.V.

In the engineering geology field increased attention has been posed in recent years to potential liquefaction mitigation interventions in susceptible sand formations. In silty sands this is a major challenge because, as the fines content increases, vibratory methods for densification become progressively less effective. An alternative mitigation technique can be the installation of Rammed Aggregate Pier® (RAP) columns that can increase the resistance of the soil, accounting for its lateral stress increase and for the stiffness increase from soil and RAP composite response. To investigate the influence of these factors on liquefaction resistance, full-scale blast tests were performed at a silty sand site in Bondeno (Ferrara, Italy) where liquefaction was observed after the 2012 Emilia-Romagna earthquake. A multidisciplinary team of forty researchers carried out devoted experimental activities aimed at better understanding the liquefaction process at the field scale and the effectiveness of the treatment using inter-related methods. Both natural and improved areas were investigated by in-situ tests and later subjected to controlled blasting. The blast tests were monitored with geotechnical and geophysical instrumentation, topographical surveying and geological analyses on the sand boils. Results showed the RAP effectiveness due to the improvement of soil properties within the liquefiable layer and a consequent reduction of the blast-induced liquefaction settlements, likely due to soil densification and increased lateral stress. The applied multidisciplinary approach adopted for the study allowed better understanding of the mechanism involved in the liquefaction mitigation intervention and provided a better overall evaluation of mitigation effectiveness.

Active deformation in the Central Apennines is mostly accommodated by NW-SE normal faults systems that produce moderate to large earthquakes at shallow depth. Recent examples include the 1915 Mw≈7 Avezzano earthquake (Fucino basin) and the 2009 Mw=6.1 L’Aquila earthquake (Aterno basin) which were both associated with major loss of life and massive damage to buildings and infrastructure. Here, we study the 40-km-long Ovindoli – Piano di Pezza – Campo Felice – Monti d’Ocre (OPCM) fault system, a major NNW-SSE system that potentially links the Fucino and the Aterno fault-systems. The OPCM exhibits linear and arcuate sections with four main segments and borders the eastern margin of the Aterno basin. Paleo-earthquake rupture data on the Piano di Pezza (PPF) and Campo Felice (CFF) faults exhibit remarkable synchronicity with the Fucino fault system, with the most recent surface-rupturing earthquake likely occurring in the XIVth century. In order to better understand the relationships between and earthquake rupture scenarios, we focus on the basin geometry and fault surface expression of the Piano di Pezza fault combining geomorphology and subsurface geophysics. We map the fault trace with unprecedented detail using terrestrial laser scanner surveys and quantify surface deformation affecting alluvial fans as well as glacial moraines. We obtain a mean vertical offset of 2.5 m +/- 0.3 m for the most recent features, well in agreement with paleoseismological data. Furthermore, we document slip distributions at different time scales along strike with a maximum value at the connection between the PPF and the OF. Beneath the scarp, geophysical data reveal a complex faulting geometry with several parallel strands and two minor blind splays. Electrical resistivity tomography images show a cumulative vertical offset of ~ 15 m affecting an interface attributed to the Last Glacial Maximum and confirm the high vertical slip across the fault zone. Gravimetric anomalies across the basin also indicate the sedimentary fill has recorded a maximum finite cumulative throw of the PdP fault system of 110-140 m. This suggests a maximum vertical slip rate of 0.2-0.3 mm/year since the Pleistocene, which contrasts with the high post-LGM slip rate estimated from trenches. Overall, our observations suggest that the arcuate PPF originally formed as a reverse fault during the Mio-Pliocene compressive stage and is now reactivated as an extensional horsetail-like feature by ruptures along a major strike-slip fault (OF). This finding points to the PPF as mostly built through ruptures along the OF leaking onto an inherited structure. The time-varying slip rates may also denote an episodic behavior marked by short periods of high seismic activity (a few centuries) and long intervals of seismic quiescence (a few millennia). Furthermore, possible earthquake rupture scenarios along the OPCM may encompass the whole OPCM fault system (cumulative length ca. 40 km) or rupture termination along the PPF (cumulative length ca. 15-20 km) with significantly different impacts over the populated Fucino and Aterno basins.