INGV Sezione di Pisa

We describe the main structure and outcomes of the new probabilistic seismic hazard model for Italy, MPS19 [Modello di Pericolosità Sismica, 2019]. Besides to outline the probabilistic framework adopted, the multitude of new data that have been made available after the preparation of the previous MPS04, and the set of earthquake rate and ground motion models used, we give particular emphasis to the main novelties of the modeling and the MPS19 outcomes. Specifically, we (i) introduce a novel approach to estimate and to visualize the epistemic uncertainty over the whole country; (ii) assign weights to each model components (earthquake rate and ground motion models) according to a quantitative testing phase and structured experts’ elicitation sessions; (iii) test (retrospectively) the MPS19 outcomes with the horizontal peak ground acceleration observed in the last decades, and the macroseismic intensities of the last centuries; (iv) introduce a pioneering approach to build MPS19_cluster, which accounts for the effect of earthquakes that have been removed by declustering. Finally, to make the interpretation of MPS19 outcomes easier for a wide range of possible stakeholders, we represent the final result also in terms of probability to exceed 0.15 g in 50 years.

Mefite d'Ansanto, southern Apennines, Italy is the largest natural emission of low temperature CO 2 rich gases, from non‐volcanic environment, ever measured in the Earth. The emission is fed by a buried reservoir, made up of permeable limestones and covered by clayey sediments. We estimated a total gas flux of ∼2000 tons per day. Under low wind conditions, the gas flows along a narrow natural channel producing a persistent gas river which has killed over a period of time people and animals. The application of a physical numerical model allowed us to define the zones which potentially can be affected by dangerous CO 2 concentration at breathing height for humans. The geometry of the Mefite gas reservoir is similar to those designed for sequestering CO 2 in geological storage projects where huge amounts of CO 2 should be injected in order to reduce atmospheric CO 2 concentration. The approach which we have used at Mefite to define hazardous zones for the human health can be applied also in case of large CO 2 leakages from storage sites, a phenomena which, even if improbable, can not be ruled out.

Viscosity has been determined during isothermal crystallization of an andesite from Tungurahua volcano (Ecuador). Viscosity was continuously recorded using the concentric cylinder method and employing a Pt-sheathed alumina spindle at 1 bar and from 1400°C to subliquidus temperatures to track rheological changes during crystallization. The disposable spindle was not extracted from the sample but rather left in the sample during quenching thus preserving an undisturbed textural configuration of the crystals. The inspection of products quenched during the crystallization process reveals evidence for heterogeneous crystal nucleation at the spindle and near the crucible wall, as well as crystal alignment in the flow field. At the end of the crystallization, defined when viscosity is constant, plagioclase is homogeneously distributed throughout the crucible (with the single exception of experiment performed at the lowest temperature). In this experiments, the crystallization kinetics appear to be strongly affected by the stirring conditions of the viscosity determinations. A TTT (Time-Temperature-Transformation) diagram illustrating the crystallization "nose" for this andesite under stirring conditions and at ambient pressure has been constructed. We further note that at a given crystal content and distribution, the high aspect ratio of the acicular plagioclase yields a shear-thinning rheology at crystal contents as low as 13 vol %, and that the relative viscosity is higher than predicted from existing viscosity models. These viscosity experiments hold the potential for delivering insights into the relative influences of the cooling path, undercooling, and deformation on crystallization kinetics and resultant crystal morphologies, as well as their impact on magmatic viscosity.

GINGERino is a large frame laser gyroscope investigating the ground motion in the most inner part of the underground international laboratory of the Gran Sasso, in central Italy. It consists of a square ring laser with a 3.6 m side. Several days of continuous measurements have been collected, with the apparatus running unattended. The power spectral density in the seismic bandwidth is at the level of 10−10 (rad/s)/Hz. A maximum resolution of 30 prad/s is obtained with an integration time of few hundred seconds. The ring laser routinely detects seismic rotations induced by both regional earthquakes and teleseisms. A broadband seismic station is installed on the same structure of the gyroscope. First analysis of the correlation between the rotational and the translational signal is presented.

A new 2D/3D Lagrangian particle model (named LPAC) for the dynamics of clasts ejected during explosive eruptions is presented. The novelty of the model lies in the one‐way coupling of the carrier flow field, given by a Eulerian multiphase flow code, and the particles. The model is based on a simplification of the Basset‐Boussinesq‐Oseen equation, expressing the Lagrangian equation of a particle as the sum of the forces exerted on it along its trajectory. It is assumed that particles are non‐interacting and do not affect the background carrier flow and that the drag coefficient is constant. The model was applied to large clasts produced by Vulcanian explosions, in particular those occurring in August 1997 at Soufrière Hills Volcano, Montserrat (West Indies, UK). Simulation results allowed parametric studies as well as semi‐quantitative comparisons between modeling results and field evidence. Major results include (1) the carrier flow was found to play a fundamental role even for meter‐sized particles—a 1 m diameter block is predicted to reach a distance that is about 70% greater than that predicted without the effect of the carrier flow (assuming the same initial velocity), (2) assumption of the initial velocity of the particle was dropped thanks to the description of both the acceleration and deceleration phases along the particle trajectory, (3) by adopting experimentally based drag coefficients, large particles were able to reach greater distances with respect to smaller particles consistently with field observations and (4) the initial depth of the particle in the conduit was found to mainly influence the ejection velocity while the initial radial position with respect to the conduit axis was found to play a major role on the distance reached by the particle.

Abstract Central Italy is characterized by a network of active faults that interact in a complex manner. Coseismic Coulomb stress changes have been invoked by several authors to explain the concentration of moderate‐to‐strong earthquakes in this region, but none has considered the time‐dependent viscoelastic relaxation of the lower crust and upper mantle as a possible additional source of stress changes at a regional scale. Here starting from the 1915 M w 6.9 ± 0.2 Fucino earthquake, we calculated the coseismic plus postseismic Coulomb failure stress changes (ΔCFS) due to eight moderate‐to‐strong earthquakes that have struck Central Italy in the last century and culminated with the 2016–2017 sequence. Results from this modeling coupled with some synthetic tests simulating normal fault earthquakes with different magnitudes allowed us to highlight the importance of postseismic processes. In particular, the viscoelastic stress transfer due to events of M w ≥ 6.5 can modify the spatial distribution of ΔCFS on a centennial timescale and therefore trigger events at larger distances. In addition, using these results, we identified other earthquake clusters in the historical catalogue (last 618 years), which, like the 1915–2017 series, were potentially modulated by both coseismic and postseismic processes. Finally, considering our calculations combined with historical and paleoseismological data, we suggest that several faults in Central Italy may be at present close to failure.

ABSTRACT In the last 10 yr, the International Atomic Energy Agency (IAEA) revised its safety standards for site evaluations of nuclear installations in response to emerging fault displacement hazard evaluation practices developed in Member States. New amendments in the revised safety guidance (DS507) explicitly recommend fault displacement hazard assessment, including separate approaches for candidate new sites versus existing sites. If there is insufficient basis to conclusively determine that a fault is not capable of surface displacement at an existing site, then a probabilistic fault displacement hazard analysis (PFDHA) is recommended to better characterize the hazard. This new recommendation has generated the need for the IAEA to provide its Member States with guidance on performing PFDHA, including its formulation and implementation. This article provides an overview of current PFDHA state-of-practice for nuclear installations that is consistent with the new IAEA safety standards. We also summarize progress in an ongoing international PFDHA benchmark project that will ultimately provide technical guidance to Member States for conducting site-specific fault displacement hazard assessments.

Abstract The quantification of eruptive activity represents one major challenge in volcanology. Digital comparison of lidar‐based elevation models of Etna (Italy) was made to quantify the volumes of volcanics emitted in 2007–2010. During this period, Etna produced several summit paroxysms followed by a flank eruption. We integrated the total volume difference resulting from the subtraction of the 2007 and 2010 digital elevation models with volumes of eruptive products based on field and aerial surveys to attribute volumes with hitherto unrealized precision to poorly constrained eruptions. The total erupted volume of 2007–2010 is >86 × 10 6 m 3 , most (~74 × 10 6 m 3 ) of which is made up by the lava flows of the 2008–2009 flank eruption. The survey also reveals the high lava volume (5.73 × 10 6 m 3 ) and average eruption rate (~400 m 3 s −1 ) of the 10 May 2008 paroxysm, whose flow front stopped 6.2 km from the vent, not far from the town of Zafferana Etnea.

The 17 January 2002 fissure eruption of Mount Nyiragongo, Democratic Republic of Congo, produced lava flows which entered and devastated the densely inhabited town of Goma. The 2002 and previous 1977 eruptions demonstrate the high level of volcanic risk in the area. We present an analysis of the susceptibility to lava flow invasion in Goma, by means of computer simulations based on the steepest descent path and probabilistic‐computed flow spreading and obstacle overcoming. The DEM is obtained from a topographic map of Goma by using the DEST algorithm. The numerical results show the distribution of probable lava flow paths from possible vents in the investigated topographic domain. Numerical simulations are validated through comparison with the mapped paths of the 2002 lava flows in Goma. The subsequent investigation includes the analysis of (1) hypothetical lava flow paths from ephemeral vents on the edge of the 2002 lava flows, (2) paths from venting along the hypothetical extension of the 2002 fissures, (3) paths in case of lava flow arrival in town from the north, and (4) changes induced by the presence of the solidified 2002 lava field. The results show the susceptibility of the different parts of the town of Goma to be invaded by future lava flows, and reveal the existence of a large area in town with minimum susceptibility and which can be invaded only in case of venting within it. The areas destroyed by the 2002 lava flows are predicted to be characterized by maximum susceptibility to lava flow invasion.

Abstract In the northern Tyrrhenian Sea, the Elba Island is one of the westernmost portions of the northern Apennine inner belt. One of its noteworthy features is the anomalous tectonic repetition of continental‐derived (Tuscan Unit) and oceanic‐derived (Ligurian units) thrust sheets, lately intruded by late Miocene granitoids. Moreover, in detail, a slice of strongly deformed Ligurian peridotites results tectonically sandwiched between two thrust sheets of Tuscan units. This tectonic setting results from a middle Miocene folding and thrusting of the Apenninic nappe stack with development of large‐scale antiform and out‐of‐sequence thrust. In central‐eastern Elba Island, the folding of an imbricate stack is bracketed between Langhian (middle Miocene) and Messinian (late Miocene). Consequently, the anomalous repetition of Tuscan and Ligurian units thrust sheets gives evidence of middle‐late Miocene shortening deformation post‐dating nappe stack and pre‐dating late Miocene–Pliocene granite emplacement. We suggest that the architecture of the Elba Island nappe stack documents the coexistence of early‐middle Miocene contractional and extensional tectonics in an overall convergent tectonic setting in the westernmost zone of northern Apennines. Extensional tectonics in the upper portion of the wedge, balancing transient gravitational instabilities due to over‐thickened conditions, were followed by a renewal of contractional deformation leading to development of large‐scale out‐of‐sequence thrust responsible for inversion of the stack order. Copyright © 2016 John Wiley & Sons, Ltd.

Abstract The dynamics of the 2–12 January 2010 effusive eruption at Piton de la Fournaise volcano were examined through seismic and infrasound records, time‐lapse photography, SO 2 flux measurements, deformation data, and direct observations. Digital elevation models were constructed for four periods of the eruption, thus providing an assessment of the temporal evolution of the morphology, the volume and the extrusion rate of the lava flow. These data were compared to the continuous recording of the seismic and infrasonic waves, and a linear relationship was found between the seismic energy of the tremor and the lava extrusion rate. This relationship is supported by data from three other summit eruptions of Piton de la Fournaise and gives total volume and average lava extrusion rate in good agreement with previous studies. We can therefore provide an estimate of the lava extrusion rate for the January 2010 eruption with a very high temporal resolution. We found an average lava extrusion rate of 2.4 m 3 s −1 with a peak of 106.6 m 3 s −1 during the initial lava fountaining phase. We use the inferred average lava extrusion rate during the lava fountaining phase (30.23 m 3 s −1 ) to estimate the value of the initial overpressure in the magma reservoir, which we found to range from 3.7×10 6 Pa to 5.9×10 6 Pa. Finally, based on the estimated initial overpressure, the volume of magma expelled during the lava fountaining phase and geodetic data, we inferred the volume of the magma reservoir using a simple Mogi model, between 0.25 km 3 and 0.54 km 3 , which is in good agreement with previous studies.

Abstract Tephra fallout hazard assessment is undertaken with probabilistic maps that rely on numerical models. Regarding maps production, the input parameters of the model (including atmospheric conditions), the physical approximations of the numerical simulations, and the probabilities of occurrence of different eruption types in specific time frames are among the most critical sources of uncertainty. We therefore present a tephra fallout hazard assessment study for two active volcanoes (Cotopaxi and Guagua Pichincha) in Ecuador. We utilize PLUME‐MoM/HYSPLIT models, and a procedure for uncertainty quantification where: (a) the uncertainty on eruptive source parameters and eruption type occurrence is quantified through expert elicitation; (b) we implement a new procedure for correlations between the different parameters, and (c) we use correction coefficients to take into account the uncertainty of the numerical model. Maps of exceedance probability given a deposit thickness threshold, and thickness maps given a probability of exceedance, are produced (a) for two eruptive scenarios (sub‐Plinian and Plinian) and (b) as a combination of these scenarios in case the next eruption will be sub‐Plinian or Plinian. These maps are described according to the uncertainty distribution of eruption type occurrence probabilities, considering their 5th percentile, mean, and 95th percentile values. We finally present hazard curves describing exceeding probabilities in 10 sensitive sites within the city of Quito. Additional information includes the areal extent and the population potentially affected by different isolines of tephra accumulation. This work indicates that full uncertainty quantification helps in providing more robust scientific information, improving the hazard assessment reliability.

Due to its very low solubility in silicate melts, CO 2 concentrations in melt inclusions (MIs) within crystals are commonly orders of magnitude less than the total concentration in the multiphase magma, strongly limiting the possibility to constrain CO 2 abundance based on the dissolved quantities. Here we develop a statistical method to process MI data, which allows analytical uncertainties to be taken into account together with the peculiar features of the local saturation surface. The method developed leads to retrieve total H 2 O and CO 2 concentrations in magma as well as the gas phase abundance at the time of magma crystallization. Application to a set of 29 high‐resolution secondary ion mass spectrometry (SIMS) MI data from a single specimen of the 1842–1844 eruption of Kilauea, Hawaii, reveals the existence of heterogeneous total CO 2 abundance, and of at least 2–6 wt % total CO 2 in some magma batches, two orders of magnitude higher than the dissolved amounts and 30–50 times more abundant than the corresponding total H 2 O content. Heterogeneous total volatile concentrations are interpreted as due to a combination of degassing and gas flushing in magma subject to convective motion at shallow depth where P < 100 MPa. In such a view, the magma rising to shallow depth in the volcanic system carries initially a total volatile content ≤1 wt %, corresponding to the determined low total CO 2 population, and consistent with previous global estimates. The high CO 2 populations correspond to progressive CO 2 enrichment due to degassing at low P and flushing from a deep CO 2 ‐rich gas. A total CO 2 content >1 wt % is likely to characterize the >30 km deep magma, not represented in the analyzed inclusions, from which a CO 2 ‐rich gas phase exsolves and decouples from the liquid.

SUMMARY A model for multidimensional compressible two‐phase flow with pressure and velocity relaxations based on the theory of thermodynamically compatible system is extended to study liquid–gas flows with cavitation. The model assumes for each phase its own pressure and velocity, while a common temperature is considered. The governing equations form a hyperbolic system in conservative form and are derived through the theory of a thermodynamically compatible system. The phase pressure‐equalizing process and the interfacial friction are taken into account in the balance laws for the volume fractions of one phase and for the relative velocity by adding two relaxation source terms, while the phase transition is introduced into the model considering in the balance equation for the mass of one phase the relaxation of the Gibbs free energies of the two phases. A modification of the central finite‐volume Kurganov–Noelle–Petrova method is adopted in this work to solve the homogeneous hyperbolic part, while the relaxation source terms are treated implicitly. In order to investigate the effect of the mass transfer in the solution, a 1D cavitation tube problem is presented. In addition, two 2D numerical simulations regarding cavitation problem are also studied: a cavitating Richtmyer–Meshkov instability and a laser‐induced cavitation problem. Copyright © 2014 John Wiley & Sons, Ltd.

ABSTRACT Patagonia Argentina is a key area for the study of sea level changes in the southern hemisphere, but the availability of reliable sea level markers in this area is still problematic. In fact the storm deposits (beach ridge) commonly used here to reconstruct past sea level oscillations introduce a wide error. Along the Puerto Deseado coast (Santa Cruz), morphometric analyses of 11 features were carried out using traditional measurement tools and a digital software‐based method (tested on one selected feature) with the aim to investigate the possibility of their use as sea level markers. By undertaking accurate topographic profiles we identified the relationship between notches and current sea level. In detail, we identified two clusters of notch retreat point elevations, with a very low internal variability. The lower was located a little below the mean high tide level (mHT) and the upper located at least 0.5 m above the maximum high tide level (MHT). Field observations of tidal levels and the position of notches suggest that the lower notches are active and the upper are inactive. This study on the abrasive notches attests their quality as sea level markers and opens up the use of fossil abrasive notches as palaeo sea level markers because the error linked to these features is substantially smaller than that introduced by beach ridges commonly used in the study area. Copyright © 2014 John Wiley & Sons, Ltd.

The NW submarine portion of Stromboli volcano has been investigated by deep‐towed sidescan sonar, bathymetric surveys, video camera runs and dredging during two research cruises in 2002 and 2004. The surveys resulted in the identification of an extensive pillow lava field (10 6 ‐10 7 m 3 ) at about 2300 m of water depth and 9 km from the shoreline of Stromboli Island. The pillow lavas have a unique composition that does not match any known subaerial product, although a limited affinity exists with those erupted during the Neostromboli eruptive cycle of the island (13–6 ka). This is the first finding of a submarine eruption on the northern side of Stromboli and improves the knowledge of its flank activity and volcanic hazards. This eruption is interpreted as marking the onset of a new volcanic cycle from the edifice periphery fed by a new, distinct magma mixed with traces of the previous magma that survived the emptying of the Neostromboli magma chamber.

Glass fragments in tephra erupted at Mt. Etna from May to December 1995 have been analyzed by laser ablation ICPMS. The trace element compositional variability of ashes deposited during this interval reveals the presence of discrete magma batches with different crystallization degrees in the shallow plumbing system. From May to October a highly crystalline magma is predominant within the conduit with only minor sporadic input of fresh and more primitive magma batches. After October new and less evolved magma batches become more prevalent and become progressively homogenized within more evolved resident magma. In December ashes closely match the chemistry of the volcanics subsequently erupted till February 1996. This study demonstrates that the trace element characterization of ashes has important implications for volcanic monitoring and is a useful tool for the forecasting of paroxysmal events at Mt. Etna.

Abstract Rapid assessment of the volume and the rate at which gas and pyroclasts are injected into the atmosphere during volcanic explosions is key to effective eruption hazard mitigation. Here, we use data from a dense infrasound network deployed in 2017 on Mt. Etna, Italy, to estimate eruptive volume flow rates (VFRs) during small gas‐and‐ash explosions. We use a finite‐difference time‐domain approximation to compute the acoustic Green's functions and perform a full waveform inversion for a multipole source, combining monopole and horizontal dipole terms. The inversion produces realistic estimates of VFR, on the order of 4 × 10 4 m 3 /s and well‐defined patterns of source directivity. This is the first application of acoustic waveform inversion at Mt. Etna. Our results demonstrate that acoustic waveform inversion is a mature and robust tool for assessment of source parameters and holds potential as a tool to provide rapid estimates of VFR in near real time.

Abstract The increase of available seismic data prompts the need for automatic processing procedures to fully exploit them. A good example is aftershock sequences recorded by temporary seismic networks, whose thorough analysis is challenging because of the high seismicity rate and station density. Here, we test the performance of two recent Deep Learning algorithms, the Generalized Phase Detection and Earthquake Transformer, for automatic seismic phases identification. We use data from the December 2019 Mugello basin (Northern Apennines, Italy) swarm, recorded on 13 permanent and nine temporary stations, applying these automatic procedures under different network configurations. As a benchmark, we use a catalog of 279 manually repicked earthquakes reported by the Italian National Seismic Network. Due to the ability of deep learning techniques to identify earthquakes under poor signal‐to‐noise‐ratio (SNR) conditions, we obtain: (a) a factor 3 increase in the number of locations with respect to INGV bulletin and (b) a factor 4 increase when stations from the temporary network are added. Comparison between deep learning and manually picked arrival times shows a mean difference of 0.02–0.04 s and a variance in the range 0.02–0.07 s. The improvement in magnitude completeness is ∼0.5 units. The deep learning algorithms were originally trained using data sets from different regions of the world: our results indicate that these can be successfully applied in our case, without any significant modification. Deep learning algorithms are efficient and accurate tools for data reprocessing in order to better understand the space‐time evolution of earthquake sequences.

Volcanic eruptions are often accompanied by spatiotemporal migration of ground deformation, a consequence of pressure changes within magma reservoirs and pathways. We modeled the propagation of pressure variations through the east rift zone (ERZ) of K̄lauea Volcano, Hawai‘i, caused by magma withdrawal during the early eruptive episodes (1983–1985) of the ongoing Pu‘u ‘Ō‘ō‐Kupaianaha eruption. Eruptive activity at the Pu‘u ‘Ō‘ō vent was typically accompanied by abrupt deflation that lasted for several hours and was followed by a sudden onset of gradual inflation once the eruptive episode had ended. Similar patterns of deflation and inflation were recorded at K̄lauea's summit, approximately 15 km to the northwest, albeit with time delays of hours. These delay times can be reproduced by modeling the spatiotemporal changes in magma pressure and flow rate within an elastic‐walled dike that traverses K̄lauea's ERZ. Key parameters that affect the behavior of the magma‐dike system are the dike dimensions, the elasticity of the wall rock, the magma viscosity, and to a lesser degree the magnitude and duration of the pressure variations themselves. Combinations of these parameters define a transport efficiency and a pressure diffusivity, which vary somewhat from episode to episode, resulting in variations in delay times. The observed variations in transport efficiency are most easily explained by small, localized changes to the geometry of the magma pathway.