1,721,116 research outputs found
Geophysical surveys for the restoration of Branciforte Palace in Palermo
No full textA multi-methodological and non-invasive geophysical study has been carried out in order to support the restoration project of the historic Branciforte Palace in Palermo. Ground Penetrating Radar profiles and an Electrical Resistivity Tomography ERT, carried out on the floor of the stable of the Palace, allowed to evaluate in detail the state of consolidation of the subsoil, in correspondence of a double row of marble columns, some of which were affected by differential subsidence. These columns have been investigated by means of Ultrasonic Tomography to verify their state of degradation. Moreover Infrared Thermography images of the internal and external walls and of the vaults highlighted differences in the type of masonry and in the state of the plaster. Finally the seismic characterization of the foundation soils was obtained by means of a Vertical Seismic Profile, Multichannel Analysis of Surface Waves (MASW) and Horizontal to Vertical Spectral Ratio microtremor analysis
Unconventional Arrays for 3D Electrical Resistivity and Induced Polarization Tomography to Detect Leachate Concentration in a Waste Landfill
Full text linkIn recent times, 3D electrical resistivity and induced polarization tomographies are being used more frequently. However, it is often not possible to have regular grids of electrodes due to irregular topography, difficulty accessing urbanized or industrialized places, and other environmental and health problems. In these cases, the use of unconventional arrays is necessary, arranging the electrodes around the inaccessible area according to one or more open or closed polygonal traces. In this work, three different perimeter arrangements of electrodes are considered, and, for each, three different electrode array configurations are tested by calculating their apparent resistivity and solving the inverse problem on a three-dimensional model with resistive and conductive blocks. The comparison of the results showed that the dataset that produces the most realistic inverse model consists of electrodes arranged in concentric squares and the use of the Full Range Gradient (FRG) Array. This combination was evaluated in the field on a waste landfill, in which electrical resistivity and induced polarization tomographies were carried out, exploiting the access paths to the various sectors of the landfill to arrange the electrodes on approximately concentric polygons. The 3D models of electrical resistivity and induced polarization allowed the detection of zones of high concentration of leachate, defining their extension, and monitoring the functioning of the waterproofing membrane at the bottom of the landfill. The results proved that when it is not possible to arrange a regular grid of electrodes, the use of perimeter disposals of electrode joined to the FRG array provide a sufficiently homogeneous resolution below the area to be investigated
Investigating the Internal Deterioration of the Auriga Statue of Mozia Island, Sicily, through Ultrasonic and Ground-Penetrating Radar Studies
Full text linkThe Greek marble statue of the Auriga of Mozia Island, in Sicily, is the most important artwork displayed at the Whitaker Foundation Archaeological Museum. It underwent geophysical investigations twice, in 2012 and 2021, to assess the marble’s degradation. The 2012 investigation prepared the statue for transfer to the Paul Getty Museum in New York and repositioning on an anti-seismic pedestal. The 2021 investigation evaluated potential new damage before another transfer. Both investigations utilized 3D ultrasonic tomography (UST) to detect degraded marble areas and ground-penetrating radar (GPR) to identify internal discontinuities, such as fractures or lesions, and locate metal pins that were previously inserted to reassemble the statue and its pedestal. Results from the UST indicate an average marble velocity of approximately 4700 m/s, suggesting good mechanical strength, with some areas showing lower velocities (~3000 m/s) within the material’s variability range. The GPR profiles demonstrated internal signal homogeneity, excluding internal fracture surfaces or lesions, and confirmed the presence of metallic pins. This study highlights the effectiveness of integrating UST and GPR for non-invasive diagnostics of marble sculptures, providing detailed insights into the marble’s condition and identifying hidden defects or damage
Analysis of HVSR Data Using a Modified Centroid-Based Algorithm for Near-Surface Geological Reconstruction
Full text linkRecently, the use of microtremor techniques for subsoil investigation has increased significantly. The HVSR (Horizontal to Vertical Spectral Ratio) technique allows, in many cases, to obtain a seismo-stratigraphic reconstruction of the subsoil and to identify areas with similar seismic behavior. However, the stratigraphic interpretation of the HVSR peaks still remains a subjective choice and linked to a priori information. A non-hierarchical centroid-based algorithm was modified to group HVSR peaks of different measurements that can be attributed to the same generating seismic discontinuity. Some tests performed have shown that the proposed algorithm produces valid results even in the absence of a priori information to evaluate the choice of the optimal grouping. The results obtained for HVSR measurements acquired in the city of Modica (Italy) are presented. The cluster analysis of these data and the information on the lithologies outcropping in the area made it possible to reconstruct a 3D model of the main seismo-stratigraphic discontinuities
Misinterpretation caused by 3D effects on 2D Electrical Resistivity Tomography: tests on simple models
No full textThe aim of this work is to evaluate the effects of 2D inversion of electrical resistivity data when in presence on 3D structures by testing synthetic and experimental models. Several numerical simulations have been calculated for different resistivity models and 2D datasets were extracted to study and quantify the effects of 2D inversion on 3D structures. Results have been compared with field texts carried out in quarrying sites. The main tests here presented simulates prism-shaped cavities with a square vertical section of l x l size and a variable lateral extension d, from l to infinity (this latter being a 2D tunnel model). Inversion of predicted data show that 2D tomography does not always give satisfactory results on cavities that have a more or less limited extension perpendicular to the profile. In all cases the resistivity anomaly obtained by the 2D inversion of a 3D cavity underestimates the true value much more than the inversion of the corresponding 2D model and obviously underestimation increases with three-dimensional characteristics. The effects of three-dimensionality can lead to the identification of false cavities along the vertical or can lead to strong errors in the estimation of depth and size, thus causing misleading statements
Evaluation of Artifacts and Misinterpretation in 2D Electrical Resistivity Tomography Caused by Three-Dimensional Resistive Structures of Regular or Irregular Shapes
Full text linkElectrical resistivity tomography (ERT) is a well-known geophysical method applied to geological, hydrogeological and geoenvironmental research. To date, 2D ERT is still used much more than 3D ERT, thanks to its greater immediacy, survey speed and lower complexity in processing and inversion. However, the assumption of two-dimensionality of the underground structures can mean that the effects of 3D structures on the 2D ERT can sometimes lead to gross errors in interpretation. This work aims to evaluate these effects by testing synthetic and experimental models. Numerical simulations are performed starting from different resistivity models, and from the results, 2D data sets are derived to study and quantify the effects of 2D inversion on 3D structures. Tests simulating prismatic resistive blocks with a vertical square section are presented. Prisms extend orthogonally to the survey line. Depending on their length, they range from a minimum equal to the length of the section (cubic resistive block) to infinity (2D prism). On these models, 2D and 3D electrical resistivity tomography (ERT) surveys are simulated. The results show that resistive blocks with a limited extension orthogonal to the profile are not effectively resolved by 2D ERT. Additionally, resistivity values obtained from a 2D ERT inversion on a 3D resistive prism are underestimated more than those obtained on the corresponding 2D prism when compared with the true value. This underestimation increases with the three-dimensional characteristics. Furthermore, resistive blocks located near the survey line but not crossed by it create artifacts that can lead to erroneous interpretations. A field test performed on a calcarenite quarry, of which the three-dimensional geophysical model was reconstructed, confirmed the results obtained by the synthetic tests, highlighting that the effects of three-dimensionality can lead to the identification of artifacts in the vertical section or produce strong errors in the estimation of depth and size, thus causing misleading statements
Joint Investigation with Ground Penetrating Radar and Infrared Thermography as a Diagnostic Support for the Restoration of Two Wall Mosaics in the Church of St. Mary of the Admiral in Palermo, Italy
Full text linkThe church of S. Mary of the Admiral in Palermo, known as “La Martorana” and very famous for its Byzantine mosaics, has been a World Heritage site since 2015. The mosaic system of the church includes several groups of figures and scenes from the life of the Virgin Mary. From the western part of the ancient church only two mosaics survive, detached from their original position, and are now located in two internal chapels. On the occasion of several restoration works, these two mosaic panels were investigated with non-invasive techniques, in order to provide diagnostic support to the restoration and consolidation interventions. The investigations were aimed at detecting any air pockets that could cause the detachment of the tesserae or of possible differences between cement mortars under the tesserae. For this purpose, the integrated use of two non-invasive techniques namely infrared thermography (IRT) and ground penetrating radar (GPR) was considered. The joint analysis of IRT and GPR data allowed the interpretative uncertainties inherent in each technique to be reduced. Furthermore, for both techniques differentiated analyses were performed for layers at different depths under the mosaic surface. The results of these analyses were found to be more reliable regarding GPR data, compared to infrared thermography, the latter being more influenced by the reflectivity of the tesserae. However, the results partially confirmed the restorers’ diagnosis, also allowing the identification of further critical areas that could be affected by deterioration or compositional differences in the layers supporting the mosaic
Geophysical Subsoil Characterization and Modeling Using Cluster Analysis for Seismic Microzonation Purposes
Full text linkIn the municipality of Enna, 80 HVSR measurements were performed, and some of these were combined with MASW seismic measurements, which made it possible to constrain the data inversion and obtain significant shear wave velocity models. A reconstruction of the depth of the seismic bedrock was performed for the whole territory, showing different depths for the higher and lower areas, as evidenced also by the Vseq parameter map. The frequency peaks identified in the H/V curve were analyzed through a cluster analysis algorithm to evaluate similarities that allow these peaks to be divided according to their stratigraphic origin. A non-hierarchical analysis algorithm modified in such a way as to avoid any a priori choice that could influence the partition has been used. The cluster analysis made it possible to divide the frequency peaks into five groupings, each of which was then associated with a seismic discontinuity, according to the geological contacts expected in the subsoil. Finally, the inversion of the data made it possible to reconstruct the geometries of these geological contact surfaces and to reconstruct a 3D model of the subsoil, which agrees well with the surface geology of the area
Statistical approach for cavity detection using seismic refraction and electrical resistivity data
No full textTo test limitations and effectiveness of seismic tomography when coupled to geoelectrical technique for cavity detection 2D synthetic models were used. Synthetic models were created with different number of cavity and blocks of highly cohesive lithological material (high seismic velocity and resistivity values). A modified version of multiple gradient (Martorana et al., 2016) has been used for electrical sequence. The cluster analysis performed on static units defined by electrical resistivity values, P wave velocities, and seismic density on coincident sections, allowed to interpret subsoil structures. The use of the non-hierarchical clustering algorithm has been chosen because it is less influenced by abnormal values, and allows a statistical unit to change its cluster during the iterative process.
Depending on the choice of the number of clusters to be identified, cluster distribution maps have been constructed in the multi-parameter space, allowing defining certain variability limits
for the selected parameters, for synthetic and experimental data. Finally, experimental data show that electrical and seismic tomographies is not influenced by the presence of cavities
without lateral continuity
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