Annals of Geophysics (INGV, Istituto Nazionale di Geofisica e Vulcanologia)
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Dynamics and hazards of pyroclastic avalanches at Etna volcano (Italy)
Get PDFWe present a multidisciplinary research aimed at quantifying the conditional probabilities for hazards associated with pyroclastic avalanches at Etna, which combines physical and numerical modeling of granular avalanches and probabilistic analysis. Pyroclastic avalanches are modeled using the depth-averaged model IMEX-SfloW2D, which is able to simulate the transient propagation and emplacement of granular flows generated by the collapse of a prescribed volume of granular material. Preliminary sensitivity analysis allowed us to identify the main controlling parameters of the dynamics, i.e. the total avalanche mass, the initial position of the collapsing granular mass (and the associated terrain morphology), the initial avalanche velocity, and the two rheological parameters which determine the mechanical properties of the flow. While the first two parameters can be considered as “scenario parameters” in the definition of the hazards, the initial velocity and the rheological parameters need to be calibrated. We therefore adopted a methodology for the statistical calibration of the physical model parameters based on field observations. We used data from the pyroclastic avalanche that occurred on February 10, 2022 at Etna, for which we had an accurate mapping of the deposit and some estimates of the total mass and the initial volume. We then run a preliminary ensemble of numerical simulations, with fixed initial volume and position, to calibrate the other input parameters. Based on the accuracy of the matching of the simulatedand observed deposits (measured by the Jaccard Index), we extracted from the simulation ensemble a subsample of equally probable combinations of initial velocities and rheological parameters. We then built an ensemble of model input parameters, with varying (i) avalanche volumes, (ii) initial positions, (iii) velocity, and (iv) rheological coefficients. The initial volume range was chosen within the range of observed pyroclastic avalanches at Etna (i.e., between 0.1 and 3 × 106 m3), using a prescribed probability distribution extracted from the literature data. The initial positions have been chosen on the flanks of the South East Crater of Etna, with homogeneous spatial distribution. The initial velocity and the rheological coefficients were chosen from the subsample created with the calibration. Finally, a semi-automatic procedure (digital workflow) running the Monte Carlo simulation allowed us to produce the first probabilistic map of pyroclastic avalanche invasion at Etna. Such a map, conditional to the occurrence of a pyroclastic avalanche event, can be used to identify the hazardous areas of the volcano and to plan mitigation measures
Spatial data and GIS for the assessment of the environmental impact at Mount Etna
Get PDFOne of the fundamental tasks for environmental impact assessment and natural risk management is the accurate and updated cataloging of road infrastructures and buildings. This is particularly important in volcanic areas, in order to predict the range of damage and disruption, and therefore losses and reconstruction costs that could result from an eruption. GIS allows immediate access to spatial data with the ability to overlay location-based information for easy interpretation, providing a critical tool for assessing and mitigating risk from natural phenomena. In this work, we present an innovative GIS‑based system for the identification of the values exposed to volcanic eruptions at Mount Etna, which can be used in both the readiness and response phases to a volcanic emergency. We carried out a precision mapping of buildings and road infrastructures on the flanks of the Etna volcano, giving particular attention to the exposed sensitive buildings (such as schools, barracks, hospitals, etc.) and to the construction and roofing characteristics. The result is an informative and dynamic platform that offers new opportunities and challenges to decision makers for the definition of both long‑term strategies, such as territorial planning, and short‑term strategies, for the prediction of the impact of eruptions or for managing evacuations during volcanic emergencies
Stromboli 3 July 2019 Fire: what could have happened?
Get PDFOn 3 July 2019, paroxysmal activity at the Stromboli volcano ignited a fire in the south-western sector of the island. This fire burnt the entire southern and eastern area. Thanks to the intervention of the firefighters, the fire did not spread northward, thus avoiding further damage. What could have happened if there had been no intervention? Would the fire have stopped its spread on its own, orwould it have burnt the entire island? We show through numerical simulations what could have happened if the fire had not been put out by firefighters and how numerical modelling can help plan preventive actions to avoid worst-case scenarios
Scenario impact assessment for volcanoes using the OpenQuake engine
Get PDFThis study introduces a unified framework for evaluating the physical impacts of earthquakes and volcanic eruptions on buildings, leveraging upon the existing capabilities of the OpenQuake engine for earthquake risk assessment and various existing packages for computing volcanic hazard footprints. We illustrate the capabilities of the new OpenQuake volcanic scenario module using two case studies: a VEI (Volcanic Explosivity Index) 3-4 eruption of Nevado del Ruiz volcano in Colombia and a VEI 6 eruption of Mount Pinatubo in the Philippines, employing various methods for simulating hazard footprints for tephra fall, lava flows, pyroclastic density currents, and lahars. The findings demonstrate the versatility of OpenQuake in managing diverse geohazards and its potential for further extension to other hazards, while this integration advances our ability to assess and manage disaster risk
Performance of a seismicity model based on three parameters for earthquakes (M ? 5.0) in Kanto, central Japan
Get PDFWe constructed a model of earthquakes (M ? 5.0) in Kanto, central Japan, based on three parameters: the a and
b values of the Gutenberg-Richter relation, and the ?- parameter of changes in mean event size. In our method,
two empirical probability densities for each parameter, those associated with target events (conditional density
distributions) and those not associated with them (background density distributions), are defined and assumed to
have a normal distribution. Therefore, three parameters are transformed by appropriate relations so that new parameters
are normally distributed. The retrospective analysis in the learning period and the prospective test of
testing period demonstrated that the proposed model performs better by about 0.1 units in terms of the information
gain per event than the value summed up with those of the three parameters. The results are confirmed by
a simulation with randomly selected model parameters
DSEBRA - the German Seismological Broadband Array and its contribution to AdriaArray – Deployment and performance
Get PDFThe German Seismological Broadband Array (DSEBRA) comprises 100 mobile seismological stations, which are currently contributing to the multidisciplinary international AdriaArray project, launched in 2022 to comprehensively study the Adriatic plate and its surrounding regions. The data collected in this project enable detailed monitoring of seismic activity and imaging of the crustal and upper mantle structures in the Central Mediterranean. DSEBRA stations are deployed across a wide range of geographical locations, including the Alpine foreland of Germany and Austria, the high Alps of Austria, the Pannonian Basin in Hungary, the southern Dinarides in Montenegro, Kosovo, and Albania, North Macedonia, as well as the mainland of Greece. Equipped with state‑of‑the‑art technology and featuring innovative station design and remote monitoring capabilities, these stations enable the acquisition of high‑quality data in near real‑time, which is essential for early warning systems in this seismically active region. In this study, the noise characteristics of the stations are analyzed in both the frequency and time domains, revealing significant variations that can be attributed to differences in geographical and geological settings, as well as levels of urbanization. In the frequency range of the secondary microseisms, a split in the double frequency peak is observed at the Balkan stations. This split is attributed to the simultaneous activation of two distinct source regions in the surrounding oceans. This article provides an overview of the distribution and performance of DSEBRA stations within the AdriaArray project. The contribution of DSEBRA to AdriaArray underscores the importance of well‑equipped station pools and international collaboration in achieving the scientific objectives of large‑scale seismic networks
Predict part 2: Building a Geo-Database and a 3D subsurface model for the historical center of Rome
Get PDFIn many countries, the subsurface is increasingly recognized as an integral part to urban planning, requiring detailed knowledge of the 3D subsurface geometry and properties of both natural sediments and artificial deposits. The underground data are essential for visualizing and analyzing geological features in combination with artificial structures, assessing risks related to groundwater protection, seismic hazard, and preserving archaeological heritage. Geographic information systems offer powerful tools for managing and visualizing spatial data, facilitating the creation of detailed subsurface models. In this work, a novel geo‑lithologic database has been implemented in a GIS environment to provide a comprehensive understanding of the subsurface of the Roman urban area. The Roman area, despite being located in a moderate seismic hazard zone, is exposed to a significant level of seismic risk, also due to the unique cultural heritage of its historical center. Over 800 boreholes, with average depths of 50‑60 m, were georeferenced and interpreted from a large database of civil engineering boreholes. This geodatabase (hereafter GDB) served as the basis for developing a 3D subsurface model, finalised to seismic response analyses in the framework of the INGV Dynamic Planet ST‑Predict project. In addition, the development of an implicit 3D geological model for Rome, based on stratigraphic correlations and lithofacies analysis, provides crucial input for future analyses on the Quaternary deposits of the Roman area
The OTRIONS seismic network: instrumentation upgrade and borehole installation
Get PDFThe Gargano Promontory is one of the most seismically active regions of southern Italy. Here we installed the OTRIONS seismic network consisting, at its very beginning, of 12 short period stations. The network has operated in this region since 2013, and it has been upgraded during time. Five out of these stations have been equipped with broadband sensors. More recently, we installeda posthole seismometer at the site of Lucera at a depth of 30 meters to further reduce seismic noise. In this paper, we describe the OTRIONS network upgrade and focus basic guidelines for the installation of a borehole seismometer. We have performed a post‑installation orientation considering both the polarization analysis and the correlation of seismic recordings because of the impossibility of a mechanical orientation of the sensor that rotated during the descent phase. Both methods give coherent results. We have also analysed the noise level after the station’s upgrade. The maintenance and upgrade of the seismic network is fundamental for the continuous monitoring of this area
The role of gravity in normal and reverse faulting earthquakes
Get PDFGravity is a force contributing to the strain energy and the tectonic stress driving faulting and generating earthquakes. This paper discusses the role of gravity in earthquake mechanics for different tectonic settings. Considering the stress state in normal and reverse tectonic settings, including gravity as a direct contribution to lithostatic load, it is possible to show that earthquakes on normal faults do not have a different energy source than elastic rebound and that this explains differences with reverse faulting earthquakes. The paper discusses the implications from dismissing the elastic rebound theory or limiting its validity to reverse or strike‑slip faulting, as suggested to support the graviquakes model, and the consequences on the mechanics of dip‑slip earthquakes. A simple model of tectonic stress relying on Anderson theory of faulting can describe the different stress state of normal and reverse faulting earthquakes, showing higher values of tectonic stress acting on reverse faults than normal faults, for different values of the static friction coefficient. The model shows that the difference between tectonic stress before and after a dip‑slip earthquake increases with the static friction coefficient, emphasizing the effect of the drained conditions on compressionaltectonic stress, and the negligible effect for extensional tectonic settings. Slip can occur on normal faults creating horizontal extensional deformation when the minimum stress is compressional, since extension is caused by the deviatoric stress acting on the fault plane. The different stress state can explain numerous seismological observations, likely accounting for non‑Byerlee friction, stress and strength heterogeneity and geometrical complexity. The adoption of elastic rebound does not imply that the energetics of normal and reverse faulting earthquakes is the same. Considering crustal faults as passive subjects accommodating slip caused by volume collapse contradicts geological observations of fault zone structure, laboratory experiments and the spectrum of fault slip behavior. Faults are active geological subjects characterizing the strain localization and the energy release
A Multi-method Geophysical Approach for Complex Shallow Landslide Characterization
No full textThis case study demonstrates the value of combining multiple non-invasive geophysical methods to characterize a landslide along Highway 7 near Jasper, Arkansas, USA. Geophysical testing was conducted using Multichannel Analysis of Surface Waves (MASW), Horizontal to VerticalSpectral Ratio (HVSR), and Electrical Resistivity Tomography (ERT), supplemented by select soil borings. The geophysical investigation aimed to provide a high-resolution, near-continuous view of subsurface conditions, including bedrock depth and the location of the groundwater table or highly saturated zones within the slide area. These factors are important contributors to slope instability. The MASW results revealed a highly variable depth to weathered bedrock along the observed displacement zone, with the bedrock becoming shallower downslope. The ERT data detected saturated zones associated with observed seeps and springs in the area, which were feeding water into the unstable zone. A low resistivity zone on the north side correlated to wet spots, while south of the highway, saturation occurred near the deeper bedrock interface. Additionally, a grid-based HVSR approach generated a high-resolution image of the shallow and complex bedrock topography across the slide area, providing valuable information for the slope repair design. Overall, the integrated geophysical approach offered a more sustainable, rapid, and cost-effective solution for comprehensive landslide characterization and slope stability assessment, compared to relying solely on conventional methods. The combined geophysical results provided a detailed, high-resolution understanding of the subsurface conditions influential for stability analyses and slope repair design