United States

Volcanic ash is the result of extensive magma fragmentation during eruptions. It depends upon a combination of magma properties (rheology, vesicularity, permeability, gas overpressure) and the possible involvement of external fluids during magma ascent. However, fragmentation processes during the ash-dominated, low-to-mid intensity eruptions are still a matter of debate. Combination of morpho-textural data of the erupted ash with geophysical data on the activity can inform about the energy of the activity as well as on the mechanisms of ash production and dispersal. The phase of heavy ash emission occurred during March 2016 at Copahue volcano (Argentina) generated a very low infrasonic amplitude, corresponding to low exit velocity and low magma overpressure. The apparent unbalance between measured geophysical parameters and the intensity of the activity raises a number of questions concerning the links among acoustic pressure, gas overpressure and efficiency of magma fragmentation. Generally, magma-water interaction is supposed to be the main process of magma fragmentation at Copahue. Conversely, our data on ash texture indicate that a process of magma volatile exsolution under low overpressures actively controlled the fragmentation during the investigated eruptive stage. Ash componentry also revealed that a large fraction of deposit consisted of recycled material. Therefore, comparing these results with geophysical information, we interpreted the activity as influenced by a process of energy buffering, operated by the passage of the erupting mixture through a thick layer of granular, ash-bearing crater infilling produced by the ash recycling processes. The importance of this abundant hot, vent-hosted material for the convective stability of the eruptive plume and for the ash dispersal was highlighted, with direct consequences for the assessment of the related hazard and management of eruptive crises,

SGI 2021

Mechanisms of ash production and recycling during low-energy, mid-intensity eruptions at Copahue volcano (Argentina)

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L'Istituto Nazionale di Oceanografia e Geofisica Sperimentale - OGS e il Dipartimento di Matematica e Geoscienze dell'Università di Trieste sono orgogliosi di ospitare il 90° Congresso della Società Geologica Italiana a Trieste dal 14 al 16 settembre 2021. La modalità del congresso è interamente online.

Con il motto "Geologia senza frontiere" questo evento mira a promuovere le Scienze della Terra come disciplina scientifica proiettata nel futuro, oltre i confini geografici, politici e disciplinari, per comprendere meglio l'interno del Pianeta Terra e la struttura del sottosuolo, difendere la società da pericolosi eventi geologici, comprendere meglio la variabilità climatica, pianificare l'utilizzo delle georisorse in modo etico e nel rispetto dell'ambiente.


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The National Institute of Oceanography and Experimental Geophysics - OGS and the Department of Mathematics and Geosciences of the University of Trieste are proud to host the 90th Congress of the Italian Geological Society in Trieste on 14-16 September 2021.  The Congress will be held entirely online.

With the motto "Geology Without Borders" this event aims to promote Earth Sciences as a scientific discipline projected into the future, beyond geographical, political and disciplinary boundaries, to better understand the interior of Planet Earth and the structure of the subsurface, defend society from dangerous geological events, better understand climatic variability, plan the use of geo-resources in an ethical way and respecting the environment.


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technical paper

The Friuli Venezia Giulia region (FVG) belongs to the easternmost portion of the Southern Alps, where NE-SW trending, S-SE-verging thrusts of the Southalpine Quaternary front interacts with NW-SE-striking right-lateral strike-slip fault-system that characterizes the Italian-Slovenian border area. Both fault systems are still active as testified by historical and instrumental seismicity (e.g. Rovida et al., 2021). During the last millennium six M≥6 earthquakes struck FVG and surrounding regions causing thousands of casualties and widespread damages (1348, Alpi Giulie; 1511, Friuli-Slovenia; 1928, Carnia; 1873, Alpago; 1936, Cansiglio; 1976, Friuli). Despite the abundance of scientific literature produced after the devastating 1976 Friuli earthquake sequence (see for a review Carulli, 2018), before this project FVG was not equipped with a systematic and homogeneous database of active or potential active faults based on the seismotectonic features. For this reason, the Geological Service of the Friuli Venezia Giulia Region promoted a research project in collaboration with the University of Trieste, the University of Udine and the National Institute of Oceanography and Experimental Geophysics (OGS) of Trieste in order to create a database of the active faults in FVG. Input data derives from published papers, studies and maps in FVG produced during the past 50 years and based on geological, geophysical, morphotectonic, seismological, paleoseismological data. The database is organized in direct or indirect clues on the location of active or presumably active faults, as well as on their recent activity (e.g. historical, Holocene, post-LGM, pre-LGM, Quaternary and Pre-Quaternary). These clues served to fix major tectonic structures, and to create the map of the active or presumably active faults. When data are available, the structures are characterized by a full set of geometric, kinematic and seismological parameters (e.g., slip rate, recurrence interval). Each parameter is rated for accuracy (e.g. quality index). We think that this database represents a useful tool to assess both ground shaking scenarios and surface faulting hazard.

Database of active faults in Friuli Venezia Giulia: a basic tool for seismic hazard assessment

During the last millennium, several strong earthquakes have occurred in the Umbria-Marche Apennines, which makes this area one of the most seismically active of Central Italy. Unfortunately, the lack of reliable instrumental data for strong historical seismic events, and the scarce field evidence of faulting within the Quaternary deposits, make the characterization of active seismogenic structures problematic. Moreover, although these areas have been largely studied, robust and commonly accepted seismic sources are still lacking. In this regard, GIS-aided analysis of both the topography and the river network represents excellent tools to recognise areas with different behaviour in terms of vertical motions, thus allowing to infer location of tectonic structures. A tectonic-geomorphology study of the Umbria-Marche Apennine has been carried out through a comprehensive large-scale analysis of the topography and the river network, combined with instrumental seismicity and structural geology data. The topography has been analysed by combining elevation map ad its derivative (e.g., maximum, mean, minimum and relief map) and swath profile. The latter are10 km large and runs roughly perpendicular to the main geological structures and the river valleys. River network has been analysed because rivers rapidly and consistently react to tectonic deformation, with subtle changes in topography recorded by the channels morphology and the river long profile. Moreover, most of the river long profiles show sharp change in channel slope (e.g., knickpoint). These can be either interpreted as due to either lithological or tectonic control. Moreover long profile of some tributaries where also investigated to find indicators of on-going vertical movements. Topography and river network features have been compared with historical and instrumental seismicity. This comparison suggest that some topography and river network anomalies are placed in areas where the possible epicentre of strong historical earthquakes occur (e.g., the 1741 Fabriano seismic event). In this regard, the identification of active faults and the definition of their dimensional parameters have major implications on the correct assessment of the seismic hazard for large and densely populated village of the Marche Region.

Morphostructural evidence of active tectonics in the Umbria-Marche Apennines, central Italy

The north-eastern sector of the Calabrian Arc includes the Sila Massif, Sibari plain and part of the Taranto gulf. It is a geologically complex area crossed by a system of active faults since the Middle Pleistocene that makes Calabria one of the regions with the highest seismic hazard in the Mediterranean. These faults are responsible for the morphology of the territory, characterized by high relieves and widespread landslides on a large scale, and they generated strong earthquakes in the past centuries. A first fault system is characterized by normal high-angle faults with a N-S direction which displaces the Sila batolith. Continuing towards the northern part of the area, NW-SE trending normal faults displace the Plio-Quaternary sediments. In the Corigliano-Rossano area, the Rossano Fault is the most important. It is a WNW-ESE neogenic tectonic structure characterized by a left normal-transcurrent kinematics and extending for about 12 Km with an en-èchelon arrangement. It puts the Sila Batolith in contact with Tortonian and Plio-Quaternary sediments and is responsible for the catastrophic earthquake of 1836. In this work we focused on a wide area comprised between 39.2°-39.9° N and 16.2°-17.4° E degrees, making a revision of the recent earthquakes occurred in it. We collected all focal mechanisms available in published papers and analyzing with great detail the seismicity of the last 15 years. During the last century only small to medium size earthquakes occurred in the area, both on land and offshore. The seismic catalog includes hundreds of earthquakes of magnitude M<5 recorded during the last few decades. This seismicity appears widespread through the area of our study, with depth in the range from 5 km to 40 km below sea level. Swarms of small events (M<4) are quite common in this seismogenetic area. The increased number of seismic stations available during the last decade allowed for detailed analysis of the local earthquakes. We performed a location as accurate as possible of recent earthquakes, including those occurred along the coast and offshore, and computed the focal mechanism of as many events as possible. To estimate the source kinematics of small earthquakes we applied the software FOCMEC (Snoke, 2003), based on the polarity of body waves, and the software HybridMT (Kwiatek et al., 2016), based on the area below the first P wave pulse. We obtained reliable results for more than 30 earthquakes occurred during the last 15 years (2.5 <= M <= 4.4). Results show a variety of solutions, with predominance of transtensive and reverse kinematics. The location and kinematics of recent earthquakes are in good agreement with the known faults, showing a significant correlation between the computed focal mechanisms and the direction of the tectonic structures. The source analysis of recent seismicity gives interesting insight about the offshore faults.

Seismotectonic analysis of the north-east sector of Calabrian Arc

The analysis of pressures and impacts on the Apulian aquifers, as required by the EU WFD, has evidenced physical and chemical parameters related to groundwater salinization, particularly along the coastal strip. Predisposing factors such as lithology, tectonic evolution, aquifer over-exploitation (Passarella et al., 2017), and the ongoing climate change are various. Therefore, distinguishing natural from anthropogenic sources of salinization becomes a fundamental issue for assessing the aquifer's chemical status. In this framework, isotopic measures of O, H, B, and Sr, suitably support distinguishing different sources of salinity, water-rock interaction processes, and the origin of the water molecules (Pennisi et al., 2006). This study focuses on the coastal sector of the Murgia aquifer located on the Adriatic side of the Apulia region (south Italy). It is made up of several hundred-meter-thick Mesozoic calcareous and calcareous-dolomite rocks affected by fracturing and karst phenomena. The aquifer is confined and characterized by irregular geometry. Groundwater flows to the sea where it rises in numerous coastal springs. Paleo-seawater as an additional source of salinity has been suggested by previous studies.

A multi-isotope (O, H, B, Sr) approach for identifying salinity contamination along the coastal sector of Murgia aquifer (Apulia, Southern Italy)

Environmental Tritium is a powerful tracer of groundwater age and it is a key tracer of groundwater movement. Consequently, monitoring of Tritium concentration in groundwater can be a very useful tool for the determination of recent exchanges with surface water and for the presence and the traceability of anthropogenic contributions. Tritium (3H) is a radioactive isotope of hydrogen with a half-life of 12.3 years, which emits low- energy beta particles. It is a naturally occurring radionuclide through the interaction of high-energy cosmic rays with oxygen and nitrogen atoms in the upper atmosphere. The environmental levels of Tritium increased after nuclear weapon tests between 1945 and 1963, and after that it was mainly released from nuclear facilities, especially the heavy water reactor (HWR).However, Tritium concentrations in precipitation have exponentially declined over the past decades as the anthropogenic bomb tritium peak has all but disappeared. At the present, due to the natural decay of tritium and the prohibition of nuclear activities, the activity of tritium in water decreases year by year, and environmental tritium concentrations are close to natural levels of cosmic production. To detect low concentration of tritium in water, a certain degree of enrichment is essential to obtain adequate tritium count rates, through electrolytic system. The principle of electrolytic concentration of tritium is to use the isotope fractionation effect of hydrogen isotopes in the gas and liquid phases. Water samples contain mainly HHO, HDO and some HTO molecules, so by passing an electric current through a conductive water solution, the bonds of the water molecules are broken. Discharge of hydrogen from the cathode is highly isotope-selective for protium, thus, tritium and deuterium are concentrated, leaving most of the tritium in the residual water after reduction of the water sample. One method of 3H electrolytic enrichment was developed and implement in Italy by the ENEA’s Traceability Laboratory (FSN-SICNUC-TNMT – Brasimone research center). The ENEA electrolytic enrichment procedure, which precedes the counting of tritium by liquid scintillation counting (LSC), is performed by an electrolysis system consisting of 20 steel cells, a cooling system, a temperature control unit and three multiple distillation batches for the tritium samples. At present, given the decline in tritium activity in the atmosphere and hydrosphere, low tritium concentrations in groundwater can no longer be neglected, as they can be important indicators of anthropogenic pollutants. A good contribution to the assessment of the vulnerability of aquifers from anthropogenic impact could be offered by the determination of the low tritium in groundwater via the electrolytic enrichment methodology.

Electrolytic enrichment method for the determination of tritium in aquifers: tritium as an indicator of anthropogenic pollution

Dynamic fault strength t and its evolution with seismic slip and slip rate are among the most relevant parameters in earthquake mechanics. Given the large slip rate (up to 10 m/s), displacement (up to tens of meters), effective stress (tens of MPas), typical of seismic faulting, thermo-mechanical effects are outstanding: dynamic fault strength is affected by phase changes, extreme grain size reduction, and the production of amorphous and unstable materials in the slipping zone. In the first earthquake rupture models it was proposed that fault strength decreases inversely with slip rate (t ∼ 1/V, Burridge & Knopoff, 1967). Given the lack of determination of dynamic fault strength through seismological methods, elucidating constraints may arise from experimental studies. However, the experimental evidence for the strong dependence of fault friction with slip rate has been lacking for decades. After the preliminary studies of friction in rocks at seismic slip rates (Bridgman, 1936; Spray, 1987), it has been only with the installation of dedicated machines (Tullis & Weeks, 1986; Shimamoto & Tsutsumi, 1994) that the extreme deformation conditions achieved during earthquakes have been approached in the laboratory and systematically investigated. In 1997, Tsutsumi and Shimamoto reported the first data of dynamic fault strength in cohesive rocks at seismic slip rates: this study opened a new era in experimental rock deformation. Several fault dynamic weakening mechanisms first proposed theoretically (i.e., frictional melting lubrication and, more recently, fluid thermo-mechanical pressurization and elastohydrodynamic lubrication), were eventually reproduced in the laboratory (Cornelio et al., 2019; Aretusini et al., 2021). These experiments allowed us also to explore new dynamic fault weakening mechanisms and other will be probably discovered in the future. Nevertheless, the t ∼ 1/V relation was systematically observed, independently of the rock composition and presence of fluids (e.g., Di Toro et al., 2011). Nowadays, theoretical thermo-mechanical models, calibrated by experimental measures, enable us to construct constitutive equations for dynamic fault strength which find application into numerical modeling of earthquakes ruptures for both natural and human-induced seismicity (Murphy et al., 2018). Despite these recent advancements, the activation of several proposed dynamic fault weakening mechanisms and their occurrence in natural faults are debated. In this contribution, we will focus on the technical challenges and the main limitations (i.e., poor estimate of the temperature in the slipping zone, lack of in-situ observations during rock sliding, determination of the loading conditions that lead to the transition between concurrent dynamic weakening mechanisms, etc.) of the current experimental approach to unravel earthquake-related deformation mechanisms, and their application to the study of earthquakes in nature.

Friction during earthquakes: 25 years of experimental studies

Earthquakes can produce a wide spectrum of surface deformations associated with the main events or between inter-seismic periods. The larger events (Mw > 5.5) can trigger deformations such as surface ruptures related to the activation of main active faults and/or other deformations induced by seismic shaking (e.g. landslides, creeping, sink-hole). In the last three decades remote sensing acquisitions (e.g. Synthetic Aperture Radar Interferometry, Lidar differencing, optical imagery and GPS) have reached an impressive detail, useful for detecting high accuracy deformations. In particular, Differential SAR Interferometry (DInSAR), is one of the most powerful and reliable techniques to provide a snapshot of the coseismic deformation generated by earthquakes occurred within complex geological and morphological settings. In 2016-2017, a long earthquake sequence struck the Apennines in central Italy, producing impressive surface ruptures due to the activation of the SW-dipping extensional M. Vettore fault system (VF). Most of these ruptures are attributed to the 24 August Mw 6.0 and 30 October Mw 6.5 main-shocks and have been investigated by several groups of field geologists soon after the earthquakes. The complex distribution of the observed ruptures reflects the complexity of the geological setting of the epicentral area, where a succession of both carbonate and siliciclastic rocks crops out. Here we present detailed maps of the complex deformation pattern produced by the VF during the October 2016 earthquake in central Italy, derived from ALOS-2 SAR data via DInSAR technique. On these maps, we traced a set of sections to analyse the coseismic vertical displacement, necessary to identify both surface fault ruptures and off-fault deformations, the latter not directly recognizable in the field. At a local scale, we identified a large number of surface ruptures at an unprecedented level of details, improving those previously observed in the field. At a regional scale, the deformation pattern depicts a roll-over anticline, formed at the hangingwall of a main activated fault, with a listric geometry.  The rapid detection of deformation patterns from DInSAR technique can provide important constraints on the spatial distribution of the activated fault segments and their interaction. Such information can be crucial for emergency management by civil protection and helpful to drive and support the geological field surveys during the ongoing seismic crisis. These results demonstrate how the proposed approach can be applied for any worldwide earthquake, aimed to provide a wider and faster picture of the surface deformation in areas characterized by complex geology and morphology.

Complex deformation pattern of the October 2016 central Italy earthquakes from DInSAR data

Tsunami deposits are the main evidence of past tsunami wave inundations but are inherently difficult to identify in coastal sediment sequences. The complexity of the process and the multiple interactions with the ground generate a plethora of sedimentary features such as layers of sand and gravel that were typically interpreted in the past as marine transgression events or as storm surges of extraordinary magnitude. Only in the eighties, seminal works highlighted some specific features that allow identification of their origin. Among the variety of triggering mechanisms, ﻿landslides occurring on steeply sloped coastal areas, coastal volcanoes or volcanic islands, have been shown to produce devastating tsunamis. Surprisingly, there are only a few clear examples worldwide of the relationship between volcanic activity and landslides. Based on radiocarbon ages, on stratigraphic, volcanological and archaeological evidence, three well-preserved medieval tsunami deposits were recently discovered along the coast of Stromboli volcano (Aeolian Islands, southern Italy) as shown by Rosi et al. (2019), who suggested that the destructive power of one of these events is also possibly related to a huge marine storm that devastated the port of Naples in 1343 (200 km north of Stromboli). The sedimentological study of the deposits has allowed a detailed characterization of the tsunami sequences intercalated with volcaniclastic deposits and primary tephra and allowed reconstruction of the likely sequence of the volcanic events (Pistolesi et al., 2020). In one case, a violent explosion possibly preceded the tsunami, whereas in the youngest event, the lateral collapse of the volcano flank triggered a tsunami wave that was rapidly followed by sustained explosive magmatic activity and ensuing prolonged ash venting. The hypothesized tsunami-triggering dynamics suggests a close link between volcanic activity and flank collapse, further confirming that the persistent activity at Stromboli makes the volcano particularly susceptible to tsunami generation, confirming the hazard of these phenomena at a regional scale. New stratigraphic trenches carried out in late 2020 also revealed that deeper, older tsunami deposits may be present, suggesting that tsunami and tephra deposits have recorded interactions between past eruptive activity and landslides at Stromboli volcano even further back in the past.

Eruptive activity and tsunamigenic landslides at Stromboli volcano (Italy): clues from deposits and future perspectives

2 does change owing to the volcanic degassing. Although the flux and gas composition allowed tracking the fumarolic-solfataric degassing, the emissions of carbon dioxide and hydrogen sulfide caused gas hazards. The isotopic signature allows distinguishing among various CO2 (i.e., volcanic, air, and exhaust gas derived from the burning of fossil fuel). Therefore, the stable isotopes in CO2 can help to identify the dominant gas sources at district scale based on mobile surveying, and tracking the volcanic gas hazard at Vulcano. Anomalous soil CO2 emissions were found near Faraglione settlements in addition to Palizzi, which is far enough the inhabited zone. Significant changes occurred in the CO2 degassing from these zones, because of the volcanic gas addition. This study shows the results of the survey aimed to identify four sites suitable for deployment of a monitoring system of the gas hazard at Faraglione. The survey was performed in summer 2020 and enabled collecting stable isotope composition measurements of the air CO2 and CO2 concentration indoor. The investigation targeted several types of environments including outdoor sites for a direct comparison with the indoor environment. Both the 13C/12C and 18O/16O of the air CO2 were determined by using a laser-based isotope mass spectrophotometer. A four-wheel car hosted the instrument, enabling isotopic measurements at 1 Hz, and meter-size spatial resolution. During the indoor survey, an infrared spectrophotometer enabled the air CO2 concentration measurements in the range of 0 - 10% vol. At least four measurements were performed at each site, with 2 minutes sampling frequency. The results allowed evaluating the CO2 concentration patterns in a time window (i.e., 10 minutes) comparable with the Permissible Exposure Limit (PEL). The results show that indoor air CO2 concentration was above the current average air CO2 concentration (415 ppm vol) in several selected sites. Multiple sources of gases contributed to the CO2 level in the various sites as shown by the isotope signature of the air CO2. In a few specific sites, the air CO2 concentration achieved 6% vol after a few minutes of measurement, owing to the combination of high soil CO2 emissions and reduced air circulation. This value is higher than the Immediately Dangerous to Life and Health exposure limit (IDLH = 4% vol).  The results of this study show that gas hazard mitigation includes several actions in the settled zones of Vulcano Porto. The soil CO2 flux and the air CO2 monitoring (i.e., concentration and stable isotope composition) are compelling actions to decrease the volcanic risk.

Design and implementation of the gas hazard early warning system at Vulcano - Aeolian Islands

In the past, volcanic hazard assessment was typically based on one or a few, subjectively chosen representative eruptive scenarios, using a specific combination for the values of the parameters related to the eruptive size and intensity to represent a particular eruptive size class. Recently, in modelling tephra load hazard, the natural variability in terms of eruptive size and intensity, vent position and meteorological conditions, has been taken into account (e.g., Sandri et al., 2016; Selva et al., 2018). Here, we adopted a probabilistic methodology for a novel long-term volcanic hazard analysis which accounts for intrinsic eruptive variability, to quantify tephra load hazard in Southern Italy, from Somma-Vesuvius and Campi Flegrei, on a regional target domain (ca. 600km x 600km, covering Campania, Basilicata, Apulia, Calabria, Sicily) at a 3-km resolution. Numerical simulations were performed by FALL3D model (Folch et al., 2020) in which the values for the eruption parameters are sampled within plausible ranges for given vents and size classes (Small, Medium, Large). Wind profiles have been collected from the ECMWF ERA5 from 1991 to 2020, with a spatial resolution of 0.03° x 0.03°. The results of this tephra fallout hazard scheme provided absolute hazard curves showing how the tephra load exceedance probability varies on the target domain, in 50 years. The results achieved are perfectly similar, in format. To those commonly achieved with the classic approach for probabilistic seismic hazard assessment, and perfectly compatible with fragility analysis in order to compute and rank the associated tephra load risk with the seismic and other natural risks whose hazards are calculated in the same way. Moreover, the proposed method can be extended to larger temporal intervals to quantify the volcanic hazard due to less frequent events that are relevant for the risk quantification on critical infrastructures.

Mechanisms of ash production and recycling during low-energy, mid-intensity eruptions at Copahue volcano (Argentina)

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Database of active faults in Friuli Venezia Giulia: a basic tool for seismic hazard assessment

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Mechanisms of ash production and recycling during low-energy, mid-intensity eruptions at Copahue volcano (Argentina)

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Next from SGI 2021

Database of active faults in Friuli Venezia Giulia: a basic tool for seismic hazard assessment

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Geochemistry and petrology of plagiogranites in the ophiolites from the Pollino Massif (Southern Italy): Origin and tectonic significance

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PRESENTATIONS

CONFERENCES

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RESOURCES

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