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  • 1
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    Selection of Time Windows in the Horizontal-to-Vertical Noise Spectral Ratio by Means of Cluster Analysis [Article] (2016)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2016-04-15
    Description: The selection of the elementary analysis windows in continuous noise recordings for optimal estimation of the mean horizontal-to-vertical spectral ratio (HVSR) curve is generally performed by visual inspection of HVSR curves considered as functions of time. Starting from full-length records, HVSR curves are determined in consecutive time windows of appropriate lengths. Time windows with HVSR curves that are anomalous on the basis of a simple visual inspection are generally ignored in the computation of the average HVSR curve. It is often very difficult to optimize the selection of time windows to be used for the calculation of the HVSR curve representative of a site. The use of nonobjective selection criteria produces results which depend on personal opinions of the operator and for which reliability cannot be assessed with quantitative parameters. We implemented an automatic procedure, based on cluster analysis, for the determination of the optimal window subset for the computation of the average HVSR curve. The procedure is based on the application of the agglomerative hierarchical clustering, using a measure of proximity of the standard correlation between HVSR curves and, as a rule for merging clusters, the average linking criterion. The procedure has been applied to 814 measures of seismic noise, carried out for the first-level microzonation of 20 municipalities of Eastern Sicily characterized by high seismic hazard. A critical comparison of the results obtained by the clustering procedure implemented with those previously obtained by processing the same recordings with a technique based on the visual comparison of the spectral ratios of all the analysis windows has shown that the automatic clustering procedure seems to be capable of achieving a better partitioning of a set of HVSR curves and thus provides effective help in the process of distinguishing between peaks mainly linked to the site effects and others mainly related to the source effects.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 2
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    Selection of Time Windows in the Horizontal-to-Vertical Noise Spectral Ratio by Means of Cluster Analysis (2016)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2016-04-07
    Description: The selection of the elementary analysis windows in continuous noise recordings for optimal estimation of the mean horizontal-to-vertical spectral ratio (HVSR) curve is generally performed by visual inspection of HVSR curves considered as functions of time. Starting from full-length records, HVSR curves are determined in consecutive time windows of appropriate lengths. Time windows with HVSR curves that are anomalous on the basis of a simple visual inspection are generally ignored in the computation of the average HVSR curve. It is often very difficult to optimize the selection of time windows to be used for the calculation of the HVSR curve representative of a site. The use of nonobjective selection criteria produces results which depend on personal opinions of the operator and for which reliability cannot be assessed with quantitative parameters. We implemented an automatic procedure, based on cluster analysis, for the determination of the optimal window subset for the computation of the average HVSR curve. The procedure is based on the application of the agglomerative hierarchical clustering, using a measure of proximity of the standard correlation between HVSR curves and, as a rule for merging clusters, the average linking criterion. The procedure has been applied to 814 measures of seismic noise, carried out for the first-level microzonation of 20 municipalities of Eastern Sicily characterized by high seismic hazard. A critical comparison of the results obtained by the clustering procedure implemented with those previously obtained by processing the same recordings with a technique based on the visual comparison of the spectral ratios of all the analysis windows has shown that the automatic clustering procedure seems to be capable of achieving a better partitioning of a set of HVSR curves and thus provides effective help in the process of distinguishing between peaks mainly linked to the site effects and others mainly related to the source effects.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 3
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    A new 3D model of the Ionian slab geometry and of the Central Mediterranean Moho (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-07-11
    Description: The Central Mediterranean is a geodynamically complex area resulting from the interaction between the European and African plates. This process caused strong lateral variation in lithospheric thickness and thus strong variation in the Moho topography.In this work we propose a new 3D Moho map for the Central Mediterranean, obtained from the interpolation of different data as: 2D velocity models (Scarascia et al., 1994; Chironi et al., 2000; Nicolich et al., 2000; Cassinis et al., 2005; Dellong et al., 2018; Agius et al., 2022), gravimetric profiles (Chironi et al., 2000; Dellong et al., 2018) and interpreted seismic reflection profile (Finetti et al., 2005; Civile et al., 2008; Catalano et al., 2013; Fedorik et al., 2018; Tugend et al., 2019; Sulli et al., 2021).In order to optimize the geometry of the Ionian slab, we used the hypocenters of the seismic events extrapolated from different databases. In particular, we collected relocated seismic events from 1981 to the present.We obtained a new constrained 3D Moho map for the Central Mediterranean that presents a strong lateral variation. Furthermore, the Ionian slab is quite different with respect to the model proposed by DISS (2021) and its geometry has been adapted to the hypocenters of the deepest seismic events (〉40 km deep). In particular it was verticalized starting from about 200 km depth and the width was changed depending on new available data.This model will allow a better understanding of the structure of the upper mantle and of the complex geodynamics of the area.
    Language: English
    Type: info:eu-repo/semantics/conferenceObject
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  • 4
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    Assessment of a geological model by surface wave analyses (2018)
    Details
    Publication Date: 2020-12-07
    Description: A set of horizontal to vertical spectral ratio (HVSR) and multichannel analysis of surface waves (MASW) measurements, carried out in the Altavilla Milicia (Sicily) area, is analyzed to test a geological model of the area. Statistical techniques have been used in different stages of the data analysis, to optimize the reliability of the information extracted from geophysical measurements. In particular, cluster analysis algorithms have been implemented to select the time windows of the microseismic signal to be used for calculating the spectral ratio H/V and to identify sets of spectral ratio peaks likely caused by the same underground structures. Using results of reflection seismic lines, typical values of P-wave and S-wave velocity were estimated for each geological formation present in the area. These were used to narrow down the research space of parameters for the HVSR interpretation. MASW profiles have been carried out close to each HVSR measuring point, provided the parameters of the shallower layers for the HVSR models. MASW inversion has been constrained by extrapolating thicknesses from a known stratigraphic sequence. Preliminary 1D seismic models were obtained by adding deeper layers to models that resulted from MASW inversion. These justify the peaks of the HVSR curves due to layers deeper than MASW investigation depth. Furthermore, much deeper layers were included in the HVSR model, as suggested by geological setting and stratigraphic sequence. This choice was made considering that these latter layers do not generate other HVSR peaks and do not significantly affect the misfit. The starting models have been used to limit the starting research space for a more accurate interpretation, made considering the noise as a superposition of Rayleigh and Love waves. Results allowed to recognize four main seismic layers and to associate them to the main stratigraphic successions. The lateral correlation of seismic velocity models, joined with tectonic evidences, allowed to plot two geological sections, showing the main pattern of geological formations and tectonic structures. © 2016 Sinopec Geophysical Research Institute.
    Description: Published
    Description: 159 – 172
    Description: 4T. Sismologia, geofisica e geologia per l'ingegneria sismica
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 5
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    The structure of a hydrothermal system from an integrated geochemical, geophysical, and geological approach: The Ischia Island case study (2011)
    AGU Geochemical Society
    Details
    Publication Date: 2020-11-26
    Description: The complexity of volcano-hosted hydrothermal systems is such that thorough characterization requires extensive and interdisciplinary work. We use here an integrated multidisciplinary approach, combining geological investigations with hydrogeochemical and soil degassing prospecting, and resistivity surveys, to provide a comprehensive characterization of the shallow structure of the southwestern Ischia's hydrothermal system. We show that the investigated area is characterized by a structural setting that, although very complex, can be schematized in three sectors, namely, the extra caldera sector (ECS), caldera floor sector (CFS), and resurgent caldera sector (RCS). This contrasted structural setting governs fluid circulation. Geochemical prospecting shows, in fact, that the caldera floor sector, a structural and topographic low, is the area where CO2-rich (〉40 cm3/l) hydrothermally mature (log Mg/Na ratios 〈 −3) waters, of prevalently meteoric origin (δ18O 〈 −5.5‰), preferentially flow and accumulate. This pervasive hydrothermal circulation within the caldera floor sector, being also the source of significant CO2 soil degassing (〉150 g m−2 d−1), is clearly captured by electrical resistivity tomography (ERT) and transient electromagnetic (TEM) surveys as a highly conductive (resistivity 〈 3 Ω·m) layer from depths of ~100 m, and therefore within the Mount Epomeo Green Tuff (MEGT) formation. Our observations indicate, instead, that less-thermalized fluids prevail in the extra caldera and resurgent caldera sectors, where highly conductive seawater-like (total dissolved solid, TDS 〉 10,000 mg/l) and poorly conductive meteoric-derived (TDS 〈 4,000 mg/l) waters are observed, respectively. We finally integrate our observations to build a general model for fluid circulation in the shallowest (〈0.5 km) part of Ischia's hydrothermal system.
    Description: Published
    Description: Q07017
    Description: 1.2. TTC - Sorveglianza geochimica delle aree vulcaniche attive
    Description: JCR Journal
    Description: restricted
    Keywords: ERT ; TEM ; Ischia ; fluid geochemistry ; hydrothermal systems ; resurgent caldera ; 03. Hydrosphere::03.02. Hydrology::03.02.03. Groundwater processes ; 03. Hydrosphere::03.02. Hydrology::03.02.05. Models and Forecasts ; 03. Hydrosphere::03.04. Chemical and biological::03.04.06. Hydrothermal systems ; 04. Solid Earth::04.01. Earth Interior::04.01.02. Geological and geophysical evidences of deep processes ; 04. Solid Earth::04.02. Exploration geophysics::04.02.01. Geochemical exploration ; 04. Solid Earth::04.04. Geology::04.04.09. Structural geology ; 04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 6
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    Recognition of Earthquake-Induced Damage in the Abakainon Necropolis (NE Sicily): Results From Geomorphological, Geophysical and Numerical Analyses (2018)
    Details
    Publication Date: 2020-12-07
    Description: Seismotectonic activity and slope instability are a permanent threat in the archaeological site of Abakainon and in the nearby village of Tripi in NE Sicily. In recent times, signs of an ancient earthquake have been identified in the necropolis of Aba- kainon which dating was ascertained to the first century AD earthquake. The site is located on a slope of Peloritani Mts. along the Tindari Fault Line and contains evidence for earthquake-in- duced landslide, including fallen columns and blocks, horizontal shift and counter slope tilting of the tomb basements. In this paper, we used an integrated geomorphological and geophysical analysis to constrain the landslide. The research was directed to the acquisition of deep geological data for the reconstruction of slope process and the thickness of mobilized materials. The applied geophysical techniques included seismic refraction tomography and electrical resistivity tomography. The surveys were performed to delineate the sliding surface and to assess approximately the thickness of mobilized materials. The geophysical and geomor- phologic data confirmed the presence of different overlapped landslides in the studied area. Moreover, a numerical simulation of the slope under seismic loads supports the hypothesis of a mobi- lization of the landslide mass in case of strong earthquakes (PGA〉0.3 g). However, numerical results highlight that the main cause of destruction for the Abakainon necropolis is the amplifi- cation of the seismic waves, occasionally accompanied by surficial sliding
    Description: Published
    Description: 133–148
    Description: 5T. Sismologia, geofisica e geologia per l'ingegneria sismica
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 7
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    Comparison of different sets of array configurations for multichannel 2D ERT acquisition (2018)
    Details
    Publication Date: 2020-12-07
    Description: Traditional electrode arrays such Wenner-Schlumberger or dipole-dipole are still widely used thanks to their well-known properties but the array configurations are generally not optimized for multi-channel resistivity measures. Synthetic datasets relating to four different arrays, dipole-dipole (DD), pole-dipole (PD),Wenner-Schlumberger (WS) and a modified version of multiple gradient (MG), have been made for a systematic comparison between 2D resistivity models and their inverted images. Different sets of array configurations generated from simple combinations of geometric parameters (potential dipole lengths and dipole separation factors) were tested with synthetic and field data sets, even considering the influence of errors and the acquisition velocity. The purpose is to establish array configurations capable to provide reliable results but, at the same time, not involving excessive survey costs, even linked to the acquiring time and therefore to the number of current dipoles used. For DD, PD andWS arrays a progression of different datasets were considered increasing the number of current dipoles trying to get about the same amount of measures. A multi-coverage MG array configuration is proposed by increasing the lateral coverage and so the number of current dipoles. Noise simulating errors both on the electrode positions and on the electric potential was added. The array configurations have been tested on field data acquired in the landfill site of Bellolampo (Palermo, Italy), to detect and locate the leachate plumes and to identify the HDPE bottom of the landfill. The inversion results were compared using a quantitative analysis of data misfit, relative model resolution and model misfit. The results show that the trends of the first two parameters are linked on the array configuration and that a cumulative analysis of these parameters can help to choose the best array configuration in order to obtain a good resolution and reliability of a survey, according to generally short acquisition times.
    Description: Published
    Description: 34-48
    Description: 7A. Geofisica per il monitoraggio ambientale e geologia medica
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 8
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    Inverse problem for tripotential measures in the study of buried cavities (2006)
    Details
    Publication Date: 2020-06-03
    Description: This paper presents a solution to the inverse electrical problem for the interpretation of apparent resistivity anomalies due to empty buried cavities of quasi-spherical shape when tripotential measures are carried out. The anomalies of the apparent resistivities ra,rb andrg,and the composed resistivitiesrmand rt were previously calculated for a sufficient class of spherical models of resistivity anomalies. Then, for the whole class of models, some functionals of spatial distribution of the apparent and composed resistivity were identified and analyzed. They represent the average characteristics of the anomalies and, depending in a simple way on the fundamental parameters of the sources of the anomalies (average diameter and depth), they allow reliable estimates to be determined. Among the studied functionals, those allowing the most stable and less biased estimates of the anomaly source parameters are identified by numerical simulations with random noise perturbed data. Finally the trend of standard deviation and bias of the estimates of the unknown parameters were analyzed by varying the source models and the set of functionals used for the inversion.
    Description: JCR Journal
    Description: open
    Keywords: Geoelectrical surveys ; tripotential method ; inverse problem ; synthetic tests ; cavities ; 04. Solid Earth::04.02. Exploration geophysics::04.02.04. Magnetic and electrical methods
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 3887732 bytes
    Format: application/pdf
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