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Mid- and High-Latitude Electron Temperature Dependence on Solar Activity in the Topside Ionosphere through the Swarm B Satellite Observations and the International Reference Ionosphere Model
No full textThis study focuses on the open question of the electron temperature (Te) variation with solar activity in the topside ionosphere at mid- and high latitudes. It takes advantage of in situ observations taken over a decade (2014–2023) from Langmuir probes on board the low-Earth-orbit Swarm B satellite and spanning an altitude range of 500–530 km. The study also includes a comparison with Te values modeled using the International Reference Ionosphere (IRI) model and with Millstone Hill (42.6° N. 71.5° W) incoherent scatter radar observations. The largest Te variation with solar activity was found at high latitudes in the winter season, where Te shows a marked decreasing trend with solar activity in the polar cusp and auroral regions and, more importantly, at sub-auroral latitudes in the nightside sector. Differently, in the summer season, Te increases with solar activity in the polar cusp and auroral regions, while for equinoxes, variations are smaller and less clear. Mid-latitudes generally show negligible Te variations with solar activity, which are mostly within the natural dispersion of Te observations. The comparison between measured and modeled values highlighted that future implementations of the IRI model would benefit from an improved description of the Te dependence on solar activity, especially at high latitudes.Published490OSA3: Climatologia e meteorologia spazialeJCR Journa
Tsunami risk perception of the touristic population of Stromboli Island: towards effective risk communication strategies
No full textThis study focuses on the risks that tourists would face during a tsunami on the island of Stromboli and discusses how to best inform and prepare them. Tsunamis affect coastal regions, where many of these are leisure destinations for tourists who often don't have adequate knowledge of the region's risks. Due to their proximity to the affected areas, nearsource or local tsunamis usually allow for a limited warning time, posing great challenges to the planning of effective risk mitigation action. Furthermore, tourist populations have a particular significance in studies on risk perception, since their needs intersect with those of the local population and must be taken into account. To gather key knowledge for developing robust risk communication strategies, a survey (n = 699) was conducted between July and October 2023 to assess tourists' risk perception and preparedness. The findings indicate that tourists often misdescribe tsunamis, leading to underestimation of the security threats posed by smaller events and revealing shortcomings in current communication approaches. Given the tourism industry practices on the island, effective communication strategies for tourists should prioritize providing comprehensive information within the first 24 h of their arrival. Furthermore, given the high percentage of tourists who visit the island for a few hours and within certain time slots, we invite the authorities to provide this information before disembarking on the island.In pressOS: Terza missioneJCR Journa
Unveiling a hidden fortification system at “Faraglioni” Middle Bronze Age Village of Ustica Island (Palermo, Italy) through ERT and GPR prospections
No full textWe carried out a geophysical research project in the Middle Bronze Age village of Ustica (Palermo, Sicily, Italy), named “Faraglioni Village” after the stack formations which detach from the coast north of the archaeological site. The investigation, which comprised Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR) techniques, allowed us to discover the buried foundations of an outwork fortification system never evi denced by previous archaeological studies, only hypothesised from the observation of aerial photography and partially outcropping boulders, which align roughly parallel to the main defensive wall of the Village. Our geophysical prospection involved the entire 250 m-long arc of the outward village defensive wall, with the acquisition of eleven ERT profiles and 27 GPR scans. The techniques were selected based on both favourable logistics and methods applicability: ERT sections allowed us to trace a series of high-resistivity anomalies ar ranged to form an arc-shaped structure along the perimeter of the defensive wall. GPR investigation was localised in the most accommodating patch of terrain of the site, with the effort of intercepting clear enough sections of the target, to determine more accurately its shape, depth, and overall dimensions. Our discovery paves the way for new investigations, mainly aimed at defining the timing of construction of the fortification system, as well as the function of the remains of other architectural structures identified close to the wall, which could represent the target of further geophysical investigations.Published105272OSV2: Complessità dei processi vulcanici: approcci multidisciplinari e multiparametriciJCR Journa
A model for the hydrothermal tremor source of the Mefite d'Ansanto (Italy) CO2 non-volcanic emissions in the intermediate frequency band (1-15 Hz)
No full textIn the Summer 2021 a seismic passive survey was carried out at Mefite d'Ansanto (Italy), well-known for the cold non-volcanic and lethal CO2 emissions. Mefite is located close to that part of Irpinia region hosting the large historical earthquakes' faults, that generated the destructive magnitude 6.8 earthquake of 1980 and have been related to the CO2 leakage by the scientific community. The survey was conducted by installing a small short-period seismic array with the purpose of determining the wavefield features and detecting the possible signature of the regional stress variations. By analyzing the acquired data, we have determined the properties of the seismic wavefield associated with the emission vents, in the intermediate frequency band, 1-15 Hz, which was found to be composed of a stationary background component and an intermittent higher energy one. Basing on our results, considerations on the medium properties and the deep source available information, we have depicted a schematic model of the shallow seismic source: the background components are linked to the shallower activity of the hydrothermal system, e.g. the bubbling, while the intermittent ones are likely generated by the passage of the overpressured gas, trapped in the first-tens-meters' layers, after overcoming the internal cohesion charge. The characteristics of the wavefield that we have defined, refer to a condition in which no regional earthquakes occurred and could be considered as a basis to identify possible significant variations linked to CO2 emissions and to the regional stress changes.Earthquake Department Strategic Project FURTHER “The role of FlUids in the pReparaTory pHase of EaRthquakes in Southern Apennines” of the Istituto Nazionale di Geofisica e VulcanologiaPublished19480OSV3: Sviluppo di nuovi sistemi osservazionali e di analisi ad alta sensibilitàJCR Journa
Low-strength shear zone in the western Makran subduction zone, southeastern Iran: insights from a receiver function analysis
No full textTo understand the seismic hazard of a subduction zone, it is necessary to know the geometry, location and mechanical characteristics of the interplate boundary below which an oceanic plate is thrust downward. By considering the azimuthal dependence of converted P-to-S (Ps) amplitudes in receiver functions, we have detected the interplate boundary in the Makran subduction zone, revealing significant seismic anisotropy at the base of the accretionary wedge above the slab before it bends down beneath the Jaz Murian basin. This anisotropic feature aligns with a zone of reduced seismic velocity and a high primary/secondary wave velocity ratio (Vp/Vs), as documented in previous studies. The presence of this low-velocity highly anisotropic layer at the base of the accretionary wedge, likely representing a low-strength shear zone, could possibly explain the unusually wide accretionary wedge in Makran. Additionally, it may impact the location and width of the locked zone along the interplate boundary.Iranian National Science Foundation (INSF)Published64-74OST1 Alla ricerca dei Motori GeodinamiciJCR Journa
Scenario-based seismic hazard for horizontal and vertical ground motions in central Italy
No full textWe propose an innovative methodology for seismic emergency planning and earthquake risk mitigation in central Italy by integrating three prototypal earthquake scenarios. The different scenarios derive maximum earthquake magnitudes from different input data. The first scenario utilizes local rheological, geological, and geophysical conditions; the second scenario considers the study area fault characteristics, while the third scenario relies on the cluster analysis of historical and instru- mental earthquake records. The magnitudes and related uncertainties are combined using a conflation method to derive the expected ground motions for a grid of sites in central Italy. The resulting scenarios include peak ground acceleration and spectral ordinates, presented as maps and spectra for two selected localities. The vertical component of ground motion is also presented, because it is essential for accurately assessing the response of short-period structures. Our methodology complements the more classic seismic hazard analyses, offering additional insights for earthquake contingency planning and loss analysis. The proposed methodology is flexible; multiple models and ongoing advancements in scenario practice (near-field effects, vertical ground motion, and the choice of ground motion models) can be easily incorporated, increasing the effectiveness of seismic scenario modeling in seismic emergency planning and risk mitigation.Published563–582OST2 Deformazione e Hazard sismico e da maremotoJCR Journa
Short-and Long-Term Seismic Velocity Variations and Strain Evolution at Ischia (Italy): Implications for Dynamics of the Hydrothermal System
No full textIn 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.Publishede2024GL108958JCR Journa
SISMIKO: the operational task force for seismic networks rapid deployments and integration in the INGV monitoring system
No full textSISMIKO is the operational group within the Istituto Nazionale di Geofisica e Vulcanologia responsible for deploying a temporary seismic network as a rapid response to significant seismic events [Moretti et al., 2023; https://sismiko.ingv.it/]. The purpose of the temporary seismic network is to complement the RSNi (Rete Sismica Nazionale integrata) by reducing the inter-station distances of permanent stations, where necessary. SISMIKO has a distributed structure across various INGV headquarters nationwide and in recent years has equipped itself with a consistent set of around 50 seismo-accelerometric stations and an autonomous acquisition system. This system makes the acquired data available, without restrictions, to the entire scientific community through the Italy node of the European Integrated Data Archive (EIDA [Danecek et al., 2021]) portal, ensuring a high level of data quality.
To ensure a rapid response following an earthquake and rapid integration of data collected by emergency stations, a codified procedure has been established. Through this procedure, the metadata of each station is pre-configured and the data flow coming from these stations is collected within an acquisition system [D'Alema et al., 2022]. This setting allows the rapid use, if necessary, of the data obtained by SISMIKO - after a quality control - by the seismologists on duty at the INGV Operations Room [Margheriti et al., 2021].
Today, over 100 INGV personnel join SISMIKO group: technicians, technologists and researchers from each of the headquarters distributed across the national territory. A new configuration in Activity Groups allows to coordinate the distributed personnel and to cover all the aspects in the preparation of the emergency such as the technical management of the instrumentation, the field operations, to maintain contacts with the INGV Crisis Unit and the other Operational Groups and to develop automatic procedures to analyse real time seismic data (Fig 1).
Besides the operational aspects, in recent years SISMIKO has promoted the recovery of continuous data recorded by temporary seismic stations installed during past seismic sequences such as in L'Aquila 2009, Po Plain 2012 and Central Italy 2016. By reconstructing the complete station's metadata, it is now possible to distribute the data to the scientific community through the EIDA portal.UnpublishedFerraraOST5 Verso un nuovo Monitoraggi
The Impact of Polar Vortex Strength on the Longitudinal Structure of the Noontime Mid-Latitude Ionosphere and Thermosphere
No full textGround-based ionospheric, CHAMP/STAR, and GOCE satellite neutral density ρ observations under deep solar minimum conditions were used to find whether there is a dependence of longitudinal variations on polar vortex strength. Ionospheric stations at fixed-dipole geomagnetic Φ ≈ 38° and geographic φ ≈ 40°N latitudes located in ‘near-pole’ and ‘far-from-pole’ longitudinal sectors were used in the analysis. No significant longitudinal NmF2 (electron concentration in the F2-layer maximum) dependence on the polar vortex strength was revealed. Geomagnetic control was shown to be responsible for the observed longitudinal NmF2 variations. Satellite-observed longitudinal variations in neutral density did not show any visible reaction to the polar vortex strength. However, the impact of sudden stratospheric warming (SSW) on the upper atmosphere is strong enough to change the neutral density longitudinal distribution. The impact of SSW shows a global occurrence and ‘works’ within 3–5 days in geographic coordinates in the vicinity of the SSW peak. Atomic oxygen values retrieved under ‘strong’ and ‘weak’ polar vortex strengths confirm the results obtained on longitudinal variations in NmF2 and ρ. In conclusion, no visible effects related to ‘strong’ or ‘weak’ polar vortex strengths have been revealed in either NmF2 or satellite neutral density longitudinal variations. Alternatively, such effects may be very small and therefore cannot be confirmed experimentally.Published2652OSA3: Climatologia e meteorologia spazialeJCR Journa
Exploring frictional properties of upper plate fault reactivation in subduction zones: The Atacama Fault System in northern Chile
No full textThe 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.This work was supported by FONDECYT project 1200170, the National Research Center for Integrated Natural Disaster Management (CIGIDEN) CONICYT/FONDAP project 1523A0009, and ANID Ph.D. grant 21221276 (Chilean Government). We gratefully acknowledge Chiara Cornelio for her assistance with friction experiments and data processing at the INGV. We extend our gratitude to the X-ray laboratory (XRD) of the GFZ (German Research Centre for Geosciences) and Fernando Alvarez from the Department of Geological Sciences, UCN, for their assistance with the XRD analysis. The frictional experiments were supported by the HPHT laboratory of the INGV.Published119106OST3 Vicino alla fagliaJCR Journa