Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione Roma1, Roma, Italia

Hai Sentito Il Terremoto (HSIT: Did You Feel the Earthquake?) is one of the longest-running citizen science projects on the web. Launched experimentally in 1996 and fully operational since 2007, HSIT has collected data on over 16,800 earthquakes felt in Italy through more than 1,500,000 questionnaires submitted by citizens. Of these, nearly 30,000 participants are registered with HSIT, ensuring continuous engagement across the national territory. The results of this collaboration are bidirectional: citizens contribute their experience of earthquake perception, forming a core dataset that provides localized information. In return, they receive real-time feedback on the earthquake's effects on their region, represented in macroseismic intensity using the Mercalli (MCS) and European (EMS) scales. This partnership enables seismologists to access high-resolution data for analyzing territorial responses to seismic events, including attenuation laws, identifying amplification and/or attenuation zones, and perception patterns based on urban characteristics and behavioral factors. Citizen involvement has expanded the scope of the investigation to include moderate-to-low magnitude earthquakes and distant areas affected by stronger quakes. Registered participants, in particular, gain awareness of earthquakes as ongoing, active phenomena, shifting from a perception of rare catastrophic events to a continuous focus on regional seismic risks. The HSIT project bridges the gap between scientific knowledge and common understanding, fostering a shared experience of living in earthquake-prone regions with awareness and respect for associated risks and preventive measures.

In active volcanic systems, the elevated pressurization of fluids and the movement of molten materials influence the stress state and mechanical behavior of rocks, but the direct measurement of these processes and the related evolution of rocks properties is difficult. By studying seismic velocity variations, we quantify the physical changes in rocks induced by long-term volcanic deformation and the dynamic changes associated with the 2017 Casamicciola earthquake (M w 3.9) in the active volcanic complex of Ischia Island, Italy. Our study reveals a significant dynamic velocity reduction (∼0.2%), primarily due to near-surface damage, with a permanent drop linked to documented landslides and subsidence observed immediately after the earthquake. We also identified a positive long-term linear trend in velocity variations, indicative of a generalized contraction of the Ischia Caldera, as revealed by geodetic modeling. Our results suggest a depressurization of the shallow hydrothermal system through degassing along faults or sills. Plain Language Summary Volcanic systems are influenced by a variety of complex and rapid processes, including significant temperature variations, intricate stress patterns, and changes in fluid pressure. In our study, we used seismic wave velocity measurements from ambient noise recordings and GPS data to show that seismic velocity changes are highly sensitive to depressurization, ground shaking, and damage levels. These changes reflect the pressure levels of hydrothermal and magmatic fluids in volcanic regions. Our results indicate varied shallow degassing, mainly in the northern part of the island, and lower effective stress in the southern part, where there is higher geothermal activity and highly pressurized fluids. While GPS data provide surface measurements, seismic velocity variations offer insights into the Earth's crust. Together, these measurements help us understand deformation processes at different depths, which is crucial for monitoring volcanic activity.

Airborne CO2 has played a pivotal role in maintaining the Earth's atmospheric temperature at reasonable levels throughout its history. Since the onset of the industrial revolution, the level of airborne CO2 has surged due to the combustion of hydrocarbons, leading to global warming. Hydrocarbon consumption is predominantly concentrated in metropolitan areas, driven by various human activities. Estimations of CO2 emissions into the atmosphere rely on the growth of electrical power generation through hydrocarbon combustion. This study presents the outcomes of direct measurements of stable isotope concentrations in airborne CO2 in the urban area of Rome, Italy. We focused on Rome capital city, because i) it is the most populous municipality in Italy (2.8 millions inhabitants), ii) it is the European municipality with the largest surface of green areas and iii) in its south-east sector it borders the Colli Albani quiescent volcano. The dataset encompasses stable isotope compositions and airborne CO2 concentrations gathered to investigate variations in CO2 emissions across space and time. The spatial survey conducted throughout Rome's urbanized area, on a 250 km long path, aims to pinpoint the relevant sources of CO2 based on the stable isotope signature. Results reveal that the combustion of fossil fuels, stemming from urban mobility and household heating, constitutes the predominant source for the excess of airborne CO2 across a wide area of Rome centre. On the contrary, within the Rome south-east sector, including Colli Albani periphery, the carbon isotopic signature of airborne CO2 discloses the endogenous origin of the gas emissions. Continuous monitoring was carried out by the installation of an isotope analyser in three specific points of interest throughout Rome: the busiest area of the city centre, the woodland urban park of Villa Ada and the endogenous gas emission of Cava dei Selci. Findings unveil cyclic variations in human-related CO2 emissions in the city centre. The highest concentrations of airborne CO2 coincide with rush hours during morning and evening. The urban park is not affected by anthropic CO2 and its trend displays the typical day-night cycle. At Cava dei Selci we found high CO2 concentrations by a volcanic source and variations in the urban area correlate with changes in environmental conditions, such as wind speed and direction.

Abstract. The International Continental Scientific Drilling Program (ICDP) STAR (A Strainmeter Array Along the Alto Tiberina Fault System) drilling project aims to study the seismic and aseismic fault slip behavior of the active low-angle Alto Tiberina normal fault (ATF) in the northern Apennines, central Italy, by drilling and instrumenting six shallow boreholes (maximum depth 160 m) with seismometers and strainmeters. During the STAR fieldwork, a geophysical downhole logging campaign was carried out to define the optimal target depth for instrument deployment and formation rock characterization. In particular, the main objectives of this study were to define in situ physical properties of the rocks and the tectonic discontinuity geometry along the boreholes. The downhole logging data provide new findings and knowledge, especially with regards to physical properties such as resistivity and gamma-ray and wave velocity. The collected parameters were compared to the results of literature data collected in similar lithologies, as well as with the results of logging performed in deeper wells drilled for commercial purposes. The physical properties of the Mesozoic–early Tertiary calcareous formations show low gamma-ray values and high compressional (Vp) and shear wave (Vs) velocities (up to 5.3 and 2.9 km s−1, respectively), whereas the overlying clay-rich Late Tertiary formations exhibit high gamma-ray and low resistivity values as well as relatively low Vp and Vs values (up to 3.5 and 2.0 km s−1, respectively). The results obtained from the analysis of the orientations of the tectonic structures, measured along the six boreholes, show good agreement with the orientations of the present-day extensional stress field, which is NE–SW-oriented. Our study allowed us to bridge the gap between the physical properties obtained from literature data and those obtained from the deep well measurements, representing a possible case history for future projects. These new outcomes represent an almost unexplored window of data and will contribute to the advancement of knowledge of the physical properties of the rocks at shallow depths, which are typically overlooked.

Abstract. Earthquake hazard analyses rely on seismogenic source models. These are designed in various fashions, such as point sources or area sources, but the most effective is the three-dimensional representation of geological faults. We here refer to such models as fault sources. This study presents the European Fault-Source Model 2020 (EFSM20), which was one of the primary input datasets of the recently released European Seismic Hazard Model 2020. The EFSM20 compilation was entirely based on reusable data from existing active fault regional compilations that were first blended and harmonized and then augmented by a set of derived parameters. These additional parameters were devised to enable users to formulate earthquake rate forecasts based on a seismic-moment balancing approach. EFSM20 considers two main categories of seismogenic faults: crustal faults and subduction systems, which include the subduction interface and intraslab faults. The compiled dataset covers an area from the Mid-Atlantic Ridge to the Caucasus and from northern Africa to Iceland. It includes 1248 crustal faults spanning a total length of ∼95 100 km and four subduction systems, namely the Gibraltar, Calabrian, Hellenic, and Cyprus arcs, for a total length of ∼2120 km. The model focuses on an area encompassing a buffer of 300 km around all European countries (except for Overseas Countries and Territories) and a maximum of 300 km depth for the subducting slabs. All the parameters required to develop a seismic source model for earthquake hazard analysis were determined for crustal faults and subduction systems. A statistical distribution of relevant seismotectonic parameters, such as faulting mechanisms, slip rates, moment rates, and prospective maximum magnitudes, is presented and discussed to address unsettled points in view of future updates and improvements. The dataset, identified by the DOI https://doi.org/10.13127/efsm20 (Basili et al., 2022), is distributed as machine-readable files using open standards (Open Geospatial Consortium).

The Irpinia Fault, also known as the Monte Marzano Fault System, located in the Southern Apennines (Italy), is one of the most seismically active structures in the Mediterranean. It is the source of the 1980, Ms 6.9, multi-segment rupture earthquake that caused significant damage and nearly 3,000 casualties. Paleoseismological surveys indicate that this structure has generated at least four Mw ~ 7 surface-rupturing earthquakes in the past 2 ka. This paper presents a comprehensive, high-resolution geophysical investigation focused on the southernmost fault segment of the Monte Marzano Fault System, i.e., the Pantano-Ripa Rossa Fault, outcropping within the Pantano di San Gregorio Magno intramontane basin. The project, named TEst Site IRpinia fAult (TESIRA), was supported by the University of Napoli Federico II to study the near-surface structure of this intra-basin fault splay that repeatedly ruptured co-seismically in the past thousands of years. Our imaging approach included 2D and 3D electrical and seismic surveys, gravimetry, 3D FullWaver electrical tomography, drone-borne GPR and magnetic surveys, and CO2 soil flux assessment across the surface rupture. This multidisciplinary investigation improved our understanding of the basin shallow structure, providing an image of a rather complex subsurface fault and basin geometry. Seismic data suggest that fault activity at the Pantano segment of MMFS is characterized by a near-surface cumulative displacement greater than previous estimations, calling into question earlier assumptions about the timing of its activation. Despite some challenges with our drone-mounted survey equipment, the integrated dataset provides a comprehensive and reliable image of the subsurface structure. This work demonstrates the utility of developing an integrated approach at high-resolution geophysical imaging and interpretation of fault zones with weak morphological expressions.

This study aims to comprehensively characterize the hydro-geochemical and isotopic features of the complex groundwater system in the Pordenone Plain (northeastern Italy). The area is an important industrial and agricultural area exposed to severe anthropogenic pressure and climate change, which put its water resources at risk in terms of quantity and quality, making it of high scientific and social interest. The hydrogeological setting of the Pordenone Plain has been previously simplified as a phreatic continuous aquifer in the High Plain that changes into a multilayered aquifer system towards the Low Plain. However, this study reveals significant lithological and structural heterogeneities in the High Plain that exert a strong influence on its subsurface hydrodynamics. All waters exhibit a Ca(Mg)–HCO3 composition with relatively high Na–K values in the aquifers of the Low Plain likely related to cation exchange processes. Water stable isotopes (δ2H–H2O and δ18O–H2O) indicate that the deep aquifers in the Low Plain are confined by impermeable geological formations, such as clays and siltstones, which entirely restrict water mixing with shallower aquifers. Concurrently, tritium analysis provides evidence of slow recharge and flow rate. Three primary groundwater flows have been identified within the plain, as follows: 1) a surface flow that affects the unconfined or semi-confined aquifers of the High Plain hosted in gravelly sediments; 2) an intermediate flow fed by the pedemontane zone, which includes unconfined deep aquifers of the High Plain, semi confined/shallow aquifers (at a depth of 40–50 m) located near the resurgence belt area and karst springs located in eastern pedemontane of the Cansiglio Plateau; 3) a deep flow fed by the mountainous zone that affects the deep confined aquifers of the Low Plain. A reliable hydrogeochemical conceptual model has been developed to explain the compositional variability of the studied waters, providing valuable insights for the sustainable management of groundwater resources in the Pordenone Plain.

With this volume, Annals of Geophysics proudly presents a special issue dedicated to celebrating the anniversary of Istituto Nazionale di Geofisica e Vulcanologia (INGV) for its "25 years of geosciences for society". This collection of scientific articles is authored by dedicated researchers whose active participation and collaboration have brought prestige to both INGV and our journal. Although the list of authors is not exhaustive among the numerous past and present INGV collaborators, it offers an exciting and insightful journey through the fields of seismology, volcanology, and environmental science. This volume is divided into three parts: the first is dedicated to topics more closely related to seismology, the second to volcanology, and the last part is focused on environmental issues, including both review articles and articles addressing specific problems. There are contributions dedicated to the study of tsunamis and multi-hazard analyses, as well as articles on the history of globally significant infrastructure and sections focused on the most widely used seismological models.

Dear AG Readers,   It is with great pleasure and pride that I introduce to you this special volume of Annals of Geophysics titled “Embracing the past, empowering the present, and envisioning the future”. As Editor-in-Chief, I am thrilled to present a collection of articles that celebrates 25 years of INGV excellence, within the realm of geophysical disciplines. This volume showcases the outstanding contributions of our esteemed colleagues who have made themselves available to participate as authors in the compilation of this volume. Their participation is rooted in the numerous projects, collaborations, and cultural exchanges they have had over time with all the personnel of our Institute, which have allowed the advancement of knowledge in the various scientific disciplines covered. I extend my heartfelt gratitude to all authors, reviewers, and editorial board members whose dedication has made this milestone possible. Over the past 6 months we have worked hard to curate this special issue of Annals of Geophysics.  I would like to acknowledge the generous help of A. Grazia Chiodetti, who has been consistently present in every stage of editing the papers, and not least Emanuela Bagnato, Felicia Corsale and M. Chiara Piazza in following up with the authors and compiling the papers into the special issue. Without their assistance, the production of this volume would have been significantly more difficult, if not impossible. I'd like to finally thank Enrico Rocchetti, Simone Vecchi and Barbara Angioni for helping us have a well-made and always up-to-date website. I would like to thank all the referees for their excellent work in reviewing the scientific papers in such a short time. I invite you to explore these pages and delve into the diverse insights and discoveries that define our field. May this volume inspire further exploration and collaboration in the years to come. Warm regards, Editor-in-Chief

The Maule 2010 and Tohoku-Oki 2011 earthquakes demonstrated how dormant upper plate faults can be reactivated as normal faults by plate margin relaxation following megathrust slip. However, the reactivation mechanisms of these types of faults are yet unexplored. To provide a better understanding of these mechanisms, we collected fault core samples from fault segments of the Atacama Fault System in northern Chile. The sampled fault segments have clear morphological evidence of Quaternary reactivation as normal fault. We performed laboratory experiments to measure the fault strength, stability and dynamic weakening. We consider low-velocity tests for exploring the frictional strength and velocity dependence of friction via a double-direct shear apparatus and ii) high-velocity tests for investigating the frictional properties at seismic velocities via a rotary shear apparatus. The experiments revealed that fault cores have low frictional strength, velocity-strengthening behaviour and strong dynamic weakening. Additionally, a novel experimental procedure that simulates stress relaxation by stepwise reducing of the normal stress on the sample assembly showed: 1. Accelerating creep towards dynamic weakening in chlorite-rich gouges and 2. oscillatory sliding in fault gouges enriched in illite. By extrapolating our experimental observations to natural conditions, we conclude that stable sliding is favoured during the interseismic phase of the subduction earthquake cycle, whereas unstable sliding is favoured during the coseismic and postseismic phases. The latter occurs via normal stress reduction during the shift from interseismic compression to co- and postseismic tension at the plate margin.