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Anisotropic gradients in Iran: Quasi-Love waves illuminate the deep structure and deformation style of the Zagros, Alborz, and Kopet Dagh
No full textWe investigate the presence of the quasi-Love wave (qL) at 51 seismic stations of a temporary seismic network across the western Arabia-Eurasia collision zone. We quantify the intensity of the qL observations from the April 12, 2014 Solomon Islands earthquake by calculating the peak-to-peak amplitude ratios of the qL and Love waves, and compare them with predicted qL intensities from previous shear-wave splitting results. We determine the polarity, timing, and period-dependence of the qL observations within the period range of 50–100 s. Our analysis reveals that the qL observations at stations in the Zagros and Alborz mountain belts exhibit opposite characteristics. In contrast to the Alborz stations, the intensity of qL observations at the Zagros stations exhibits relatively negligible dependence on the period, while their receiver-scatterer distances are considerably period dependent. We approximately locate the anisotropic gradients that generate the qL waves. Our results suggest that a lithospheric gap is responsible for the shallow and abrupt variation in the belt-parallel trend of fast-axis orientations in the westernmost part of the Zagros. Additionally, the period/depth dependence of the anisotropic gradients along the boundary between the central Zagros and central Iran provides insight into the variation in the downward dip of the Arabian lithosphere. The anisotropic gradient located to the north of the Doruneh fault in eastern Iran indicates its role as a major shear zone and lithospheric boundary. Finally, we observe that the spatial distribution of the anisotropic gradient in northeastern Iran matches the higher strain rate areas in the Kopet Dagh Mountains, suggesting coupling between the lithospheric mantle and crust in that region.Published101989OST1 Alla ricerca dei Motori GeodinamiciJCR Journa
High-spectral-resolution Fabry-Pérot interferometers overcome fundamental limitations of present volcanic gas remote sensing techniques
No full textRemote sensing (RS) of volcanic gases has become a central tool for studying volcanic activity. For instance, ultraviolet (UV) skylight spectroscopy with grating spectrographs (GS) enables SO2 (and, under favourable conditions, BrO) quantification in volcanic plumes from autonomous platforms at safe distances. These measurements can serve volcanic monitoring and they cover all stages of volcanic activity in long measurement time series, which substantially contributes to the refinement of theories on volcanic degassing. Infrared (IR) remote sensing techniques are able to measure further volcanic gases (e.g., HF, HCl, CO2, CO). However, the employed Fourier transform spectrometers (FTSs) are intrinsically intricate and, due to limited resolving power or light throughput, mostly rely on either lamps, direct sun, or hot lava as light source, usually limiting measurements to individual field campaigns. We show that many limitations of grating spectrographs and Fourier transform spectrometer measurements can be overcome by Fabry-Perot interferometer (FPI) based spectrograph implementations. Compared to grating spectrographs and Fourier transform spectrometers, Fabry-Perot interferometer spectrographs reach a 1-3 orders of magnitude higher spectral resolution and superior light throughput with compact and stable set-ups. This leads to 1) enhanced sensitivity and selectivity of the spectral trace gas detection, 2) enables the measurement of so far undetected volcanic plume constituents [e.g., hydroxyl (OH) or sulfanyl (SH)], and 3) extends the range of gases that can be measured continuously using the sky as light source. Here, we present measurements with a shoe-box-size Fabry-Perot interferometer spectrograph (resolving power of ca. 150000), performed in the crater of Nyiragongo volcano. By analysing the light of a ultraviolet light emitting diode that is sent through the hot gas emission of an active lava flow, we reach an OH detection limit of about 20 ppb, which is orders of magnitude lower than the mixing ratios predicted by high-temperature chemical models. Furthermore, we introduce example calculations that demonstrate the feasibility of skylight-based remote sensing of HF and HCl in the short-wave infrared with Fabry-Perot interferometer spectrographs, which opens the path to continuous monitoring and data acquisition during all stages of volcanic activity. This is only one among many further potential applications of remote sensing of volcanic gases with high spectral resolution.Published1039093OSV3: Sviluppo di nuovi sistemi osservazionali e di analisi ad alta sensibilitàJCR Journa
The Mediterranean Forecasting System – Part 1: Evolution and performance
No full textThe Mediterranean Forecasting System produces operational analyses and reanalyses and 10 d forecasts for many essential ocean variables (EOVs), from currents, temperature, salinity, and sea level to wind waves and pelagic biogeochemistry. The products are available at a horizontal resolution of 1/24 (approximately 4 km) and with 141 unevenly spaced vertical levels.
The core of the Mediterranean Forecasting System is constituted by the physical (PHY), the biogeochemical (BIO), and the wave (WAV) components, consisting of both numerical models and data assimilation modules. The three components together constitute the so-called Mediterranean Monitoring
and Forecasting Center (Med-MFC) of the Copernicus Marine Service.
Daily 10 d forecasts and analyses are produced by the PHY, BIO, and WAV operational systems, while reanalyses are produced every 3 years for the past 30 years and are extended (yearly). The modelling systems, their coupling strategy, and their evolutions are illustrated in detail. For the first time, the quality of the products is documented in terms of skill metrics evaluated over a common 3-year period (2018–2020), giving the first complete assessment of uncertainties for all the Mediterranean environmental variable analyses.Published1483–1516OSA4: Ambiente marino, fascia costiera ed Oceanografia operativaJCR Journa
Seismic evidence of extensive microbial gas migration and trapping in submarine gas hydrates (Rakhine Basin, Bay of Bengal)
No full textSubmarine methane-rich gas hydrates in ocean sediments are a potential atmospheric greenhouse gas and energy source. It is considered that microbial methane is generally autochthonous, produced in situ within the gas hydrate stability zone with low gas flux and pressure, while thermogenic gas is allochthonous, migrated from a deeper petroleum system, with higher gas flux and pressure and therefore potentially higher energy resource and environmental impact. Here, we report on the allochthonous nature of large microbial gas hydrate deposits in the Rakhine Basin, Bay of Bengal. An innovative and automatic tool, developed to analyze high-resolution three-dimensional seismic data, allowed to detect hundreds of thousands gas occurrences throughout a 2 km thick Pliocene-Pleistocene sedimentary sequence extending below the gas hydrate stability zone. A supercharged section matching the present-day optimum temperature for microbial methanogenesis was identified. Combining seismic and geochemical data of the Rakhine Basin gas system points to a dominant microbial nature of the gas. Stacked amplitude anomalies and vertical anomaly clusters demonstrate active free-phase gas migration towards the shallow gas hydrate stability zone. The Rakhine Basin gas hydrates are the ultimate seal for the entire petroleum system and represent a case of “frozen seepage” of microbial gas with relatively high flux and pressure.Published106100OSA5: Energia e georisorseJCR Journa
Multi‐Instrument Observations of Various Ionospheric Disturbances Caused by the 6 February 2023 Turkey Earthquake
No full textIn this work, we investigate various types of ionospheric disturbances observed over Europe following the earthquake that occurred in Turkey on 6 February 2023. By combining observations from Doppler sounding systems, ionosondes, and GNSS receivers, we are able to discern different types of disturbances, propagating with different velocities and through different mechanisms. We can detect co-seismic ionospheric disturbances close to the epicenter, as well as ionospheric signatures of acoustic waves propagating as a consequence of propagating seismic waves. Unlike the vast majority of past ionospheric co-seismic disturbance studies that are primarily based on Total Electron Content variations, reflecting disturbances propagating around the F-region peak, the focus of the present study is the manifestation of disturbances at different ionospheric altitudes by exploiting complementary ionospheric remote sensing techniques. This is particularly highlighted through ionospheric earthquake-related signatures established as specific ionogram deformations known as multiple-cusp signatures which appear as additional cusps at the base of the F-region attributed to electron density irregularities generated by Rayleigh surface waves that generate acoustic waves propagating up to the ionosphere. Therefore this study underlines the advantage that multi-instrument investigations offer in identifying the propagation of earthquake-related ionospheric disturbances at different ionospheric altitudes and distances from the earthquake epicenter.Publishede2023JA031691OSA3: Climatologia e meteorologia spazialeJCR Journa
Decarbonation and clast dissolution timescales for short-term magma‑carbonate interactions in the volcanic feeding system and their influence on eruptive dynamics: Insights from experiments at atmospheric pressure
No full textWhile long-term interactions of magma with carbonate wall-rock (a.k.a. carbonate assimilation) are well-studied, only recently some experimental studies focused on short-term interactions (seconds to minutes) at magma chamber conditions (0.5 GPa and 1200 ◦C). They have shown that carbonate assimilation can effectively release CO2 and dissolve the ingested clast in syn-eruptive timescales. Carbonate wall-rock xenoliths in eruptive products can hence be seen as proof of even shallower ingestion (i.e., within the feeding dyke). To study these shallower interactions, we performed 66 experiments at atmospheric pressure (i.e., at the second endmember of the vol- canic feeding system) and at 950–1230 ◦C with varying melt compositions and limestone compositions. Decarbonation was found to be mainly dependent on temperature and limestone composition while clast dissolution is largely dependent on magma composition, temperature, pressure and interaction time. In natural systems during magma ascent and with increasing quantities of assimilated wall-rock, the magma temperature would steadily decrease, limiting its own decarbonation and assimilation ability. But even in the 950 ◦C-ex- periments decarbonation (i.e., CO2 release) remained a syn-eruptive process. We subsequently discussed the limits of carbonate assimilation as well as the potential effect of syn-eruptive addition of CO2 to the magmatic mixture on magma ascent and eruption dynamics.Published121724OSV2: Complessità dei processi vulcanici: approcci multidisciplinari e multiparametriciJCR Journa
Hydrogeochemical investigation of shallow aquifers before and after the 2012 Emilia seismic sequence (northern Italy)
No full textSoon after the MW = 6.0 main event of May 20, 2012 that struck the central part of the Emilia-Romagna region (Italy), several geochemical surveys were carried out on groundwater within the epicentral area. A total of 20 water samples were periodically collected, from May 2012 to July 2014, from shallow (up to 6 m depth) to deep (down to 175 m depth) wells within both unconfined and confined aquifers and analyzed for major ions, trace elements, dissolved gases and stable isotopes (δ2H–H2O, δ18O–H2O and δ13C-TDIC). Geochemical data were compared with previous data collected and analyzed in 2006 in a phase of absence of significant seismic activity.
Monitored waters showed concentration variations in post-earthquake sampling on a large number of geochemical parameters. Many of these variations were recorded during the co-seismic phase and were transient as the geochemical parameters returned towards pre-earthquake values over time.
The most significant transient variations involved trace elements, which generally show high sensitivity even to small variations in the surrounding environment due to their usually low concentrations in groundwater. Physical-chemical parameters (water temperature, pH, TDS) and major ions provided less unambiguous indications, whereas among dissolved gases CH4 and CO2 showed a general post-seismic increase within the unconfined aquifer. Increased contents of such gas species in both aquifers (this study) and soils (previous studies) suggest that the seismic-induced overpressure on the ground had enhancing effects on soil permeability and porosity and triggered their co-seismic migration upwards from deeper reservoirs. Water isotopes showed the systematic post-seismic change in δ2H toward heavier compositions with no significant changes in the δ18O, which was interpreted as due to isotopic exchange between water and a H2-bearing gas phase (e.g., H2S, CH4, H2) entering the system. Calculated δ13C data of CO2 suggested a relatively shallow production from both plant-root respiration and microbial-driven degradation of organic matter while the almost pure crustal origin of He (R/Ra values = 0.04–0.16 from the bubbling gas phase emitted by one of the monitored wells) reasonably excludes any evidence of both primary mantle 3He degassing and ascent of heavier CO2 from deep (mantle, decarbonation) inorganic sources.
Monitored waters which showed the most significant transient variations are aligned in the same E-W direction along which the seismicity and soil gas anomalies were distributed, at about 5 km S from the epicenter of the May 20th seismic event and along the main direction of the May 29th (MW = 5.8) event. This confirms that the transient variations have been activated by the seismic sequence in a sector of the crust where the presence of a fault/fracture system favors the intensification of processes affecting sediments and groundwater (variations of porosity/permeability of soils, the groundwater level, redox state, etc.) and which are able to explain the observed geochemical variations.
Only one sample monitored, the one closest to the epicenter of the May 20th event, showed clear geochemical evidence suggesting the hypothesis of mixing between superimposed water bodies.Published1056249T. Geochimica dei fluidi applicata allo studio e al monitoraggio di aree sismicheJCR Journa
Assessing impending hazards from summit eruptions: the new probabilistic map for lava flow inundation at Mt. Etna
No full textThe development of probabilistic maps associated with lava flow inundation is essential to assess hazard in open vent volcanoes, especially those that have highly urbanized flanks. In this study we present the new lava flow hazard map linked to the summit eruptions of Mt. Etna, which has been developed using a probabilistic approach that integrates statistical analyses of the volcanological historical data with numerical simulations of lava flows. The statistical analysis of volcanological data (including vent location, duration and lava volumes) about all summit eruptions occurred since 1998 has allowed us both to estimate the spatiotemporal probability of future vent opening and to extract the effusion rate curves for lava flow modelling. Numerical simulations were run using the GPUFLOW model on a 2022 Digital Surface Model derived from optical satellite images. The probabilistic approach has been validated through a back-analysis by calculating the fit between the expected probabilities of inundation and the lava flows actually emplaced during the 2020-2022 period. The obtained map shows a very high probability of inundation of lava flows emitted at vents linked to the South East Crater, according to the observation of the eruptive dynamics in the last decades.Published19543OSV4: Preparazione alle crisi vulcanicheJCR Journa
Analysis and Characterization of an Unclassified RFI Affecting Ionospheric Amplitude Scintillation Index Over the Mediterranean Area
No full textRadio frequency (RF) signals transmitted by Global Navigation Satellite Systems (GNSSs) are exploited as signals of opportunity in many scientific activities, ranging from sensing waterways and humidity of the terrain to the monitoring of the ionosphere. The latter can be pursued by processing the GNSS signals through dedicated ground-based monitoring equipment, such as the GNSS Ionospheric Scintillation and Total Electron Content Monitoring (GISTM) receivers. Nonetheless, GNSS signals are susceptible to intentional or unintentional RF interferences (RFIs), which may alter the calculation of the scintillation indices, thus compromising the quality of the scientific data and the reliability of the derived space weather monitoring products. Upon the observation of anomalous scintillation indices computed by a GISTM receiver in the Mediterranean area, the study presents the results of the analysis and characterization of a deliberate, unclassified interferer acting on the L1/E1 GNSS signal bands, observed and captured through an experimental, software-defined radio setup. This article also highlights the adverse impacts of the interferer on the amplitude scintillation indices employed in scientific investigations, and presents a methodology to discriminate among regular and corrupted scintillation data.Published8230 - 8248OSA3: Climatologia e meteorologia spazialeJCR Journa
Interplay Between Seismic and Aseismic Deformation on the Central Range Fault During the 2013 Mw 6.3 Ruisui Earthquake (Taiwan)
No full textThe 2013 Ruisui earthquake represents the first unequivocal evidence of the activity of the Central Range fault (CRF) in central Longitudinal Valley, Taiwan. Using a joint Bayesian finite-fault source inversion of Global Navigation Satellite System and strain time series, we infer that coseismic rupture occurred between 4 and 19 km depth with maximum slip of 0.5 m located near the hypocenter. We then apply a variational Bayesian independent component analysis approach to displacement signals to infer a 3-months long afterslip located in the near-source region. This observation represents the first evidence of aseismic slip on the CRF. Combining geodetic and seismological analysis with simulations based on rate-and-state friction mechanics, we analyze the interplay between seismic and aseismic deformation during the earthquake sequence. We observe that afterslip is the dominant postseismic deformation mechanism, with >95% of the moment being released aseismically in the postseismic phase and also likely represents the driving force controlling aftershock productivity. Finally, we infer the presence of a shallow velocity strengthening zone (∼0–4 km depth) associated with spatially heterogeneous slip during the postseismic phase with maximum slip of 0.18 m located above the zone of maximum coseismic deformation.Publishede2023JB026861OST2 Deformazione e Hazard sismico e da maremotoJCR Journa