1,720,999 research outputs found
Imaging near-surface sharp lateral variations with surface-wave methods — Part 1: Detection and location
Full text linkNear-surface sharp lateral variations can be either a target of investigation or an issue for the reconstruction of reliable subsurface models in surface-wave (SW) prospecting. Effective and computationally fast methods are consequently required for detection and location of these shallow heterogeneities. Four SWbased techniques, chosen between available literature methods, are tested for detection and location purposes. All of the techniques are updated for multifold data and then systematically applied on new synthetic and field data. The selected methods are based on computation of the energy, energy decay exponent, attenuation coefficient, and autospectrum. The multifold upgrade is based on the stacking of the computed parameters for single-shot or single-offset records and improves readability and interpretation of the final results. Detection and location capabilities are extensively evaluated on a variety of 2D synthetic models, simulating different target geometries, embedment conditions, and impedance contrasts with respect to the background. The methods are then validated on two field cases: a shallow low-velocity body in a sedimentary sequence and a hard-rock site with two embedded subvertical open fractures. For a quantitative comparison, the horizontal gradients of the four parameters are analyzed to establish uniform criteria for location estimation. All of the methods indicate ability in detecting and locating lateral variations having lower acoustic impedance than the surrounding material, with errors generally comparable or lower than the geophone spacing. More difficulties are encountered in locating targets with higher acoustic impedance than the background, especially in the presence of weak lateral contrasts, high embedment depths, and small dimensions of the object
Modelling of hydrodynamic behaviour in the Bossea aquifer system through natural radon concentrations: results and applications
No full textBossea Cave (Western Ligurian Alps) is affected by the presence of natural radon, originating from the radioactive decay of uranium and thorium isotopes contained in the Permian meta-volcanic basement of the karst aquifer. The non-chemically reactive Rn-222 concentrations have been investigated since 2003 by Bossea Underground Karst Laboratory: the diffusive and advective processes allow the reconstruction of the paths related to the inflowing water from the surface into the fractured network. Hence, radon fluctuations are cross-correlated with hydrodynamics: the transfer of gas from underground water flows is lagged behind the discharge peaks. The 45 hour delay in the upper meta-carbonate canyon and the 66 hour delay in the collapse chambers (located at the contact with the meta-volcanics) exclude the influence of external meteorological factors and confirm the double convective cell model describing the hypogeal atmospheric circulation. Different radon concentrations in water can also be detected between the main creek (Torrente Mora) and a secondary inflow (Polla delle Anatre). Although both are subjected to a piston flow hydrodynamic response, the former shows an increase in Rn during floods (with a lag of 46 hours), due to the mobilization of long-resident water volumes in karst fractures. In the latter case, there is a dilution of water in contact with radioactive elements of the impermeable basement (delayed by 6 hours and caused by volumes of neo-infiltration). In agreement with these results, radon proves to be an innovative tool to study the hydrodynamics of a karst aquifer and suggests a wide range of further cross-disciplinary applications, such as in the field of seismology
Modelling the rock mass response to changing water inflow and thermometric conditions in the Bossea mountain karst aquifer
Full text linkThe Bossea Cave is a mountain karst aquifer located in the Ligurian Alps (Piedmont, NW Italy). It develops at the contact between a Permian impermeable meta-volcanic basement and an overlying Triassic meta-carbonate sequence. This upper layer is responsible for the drainage of infiltrating water, mainly related to rainfall and snowmelt processes occurring in the aquifer’s feeding area. Since 2021, the temperature of the rock mass has been monitored through sub-hourly measurements with a resolution of one hundredth of a degree Celsius. The preliminary results suggest different behaviours across the cave: the rock mass close to the entrance is strongly influenced by meteoclimatic factors, with heat exchange between the external and hypogeal environment determined by the thermometric gradient, exhibiting both daily and long-term effects. In contrast, thermal
variations in the innermost rock are less pronounced and are mainly attributed to the propagation of a seasonal heat wave. The thermal inertia causes a delayed temperature peak during the winter months. Moreover, the hydrodynamic behaviour of the aquifer system only affects the rock temperature locally: the main water-rock heat exchange is observed in the proximity of the main drain (Torrente Mora), while this phenomenon is less
significant near the secondary vertical seepages. In parallel, a preliminary study to assess the potential seismic signature of water inflows and related modifications in the rock mass stress is ongoing. After processing data from a seismometer located inside the cave, the effects of rainfalls and snowmelt are distinguishable at specific frequency values in the spectrograms obtained from East, North and vertical channels. These findings provide a basis for future monitoring and analyses about the triggering mechanism of induced deformations in the rock mass and the evolving dynamics of cave morphology
Natural radon levels act as markers of hydrodynamic behavior in the mountain karst aquifer of Bossea Cave, Italy
Full text linkRadon originating from meta-volcanics located at the bottom of Bossea karstic mountain aquifer is subject to transport within the cave through both advective and diffusive processes. According to the double convective cell model of circulation referable to this hypogeal atmosphere, it is possible to correlate radon fluctuations with hydrodynamics, excluding the influence of external meteo-climatic factors. Transfer of gas from underground water flows presents delayed concentration maxima compared to flood peaks, amounting to 45 h in the upper meta-carbonate canyon and 66 h in the collapse chambers located at the contact with the meta-volcanics. Furthermore, different radon concentrations in water can be detected between the main creek and secondary inflows. Although both are subjected to a piston flow hydrodynamic response, the former shows an increase in radon during floods (with a lag of 46 h) due to the mobilization of long-resident water volumes in karst fractures, while in the latter case, there is a dilution of water in contact with radioactive elements of the impermeable basement (delayed by 6 h and caused by volumes of neo-infiltration). The analysis of radon emissions related to the site seismicity reveals no relationship, likely due to the low magnitudes and the predominant effect of hydrodynamics
Photogrammetry and 3-D Ultrasonic Tomography to estimate the integrity of two sculptures of the Egyptian Museum of Turin
No full textWe present a fruitful combination of geophysical tests (Ultrasonic Measurements) and photogrammetric
processing (Structure from Motion) for the analysis of the integrity of a couple of statues from the
Egyptian Museum of Turin. Aim of the study was to investigate the persistence of the exterior widespread
fractures within the sculptures. More than one hundred ultrasonic measurements were acquired on selected
travel-paths across each statue, using an ultrasonic pulse velocity instrument. Dealing with complex-shape
objects of restrained dimensions, it was very important to accurately define the three-dimensional
coordinates of sources and receivers, in order to precisely measure their distances. A 3-D model of the
statues was obtained from photogrammetric techniques. The acquired data were analyzed with both a
statistical approach and tomographic processing, comparing the use of classical and staggered grids, in
order to obtain the best fit of the local resolution. The final results revealed a valuable tool to guide the
procedures for the mobilization, transport and restoration of the sculptures
Magnetic and radar surveys at Locri Epizephyrii: A comparison between expectations from geophysical prospecting and actual archaeological findings
Full text linkIn recent years, geophysical methods have been increasingly applied as a preliminary mapping tool to guide archaeological excavations. Despite the reported growing case histories of geophysical prospections for archaeological purposes, direct comparison between expectations arising from the geophysical results and actual findings is not always systematically performed. A critical comparison between pre-excavation geophysical-guided hypotheses and post-excavation archeological evidences is proposed in this work. A test site within the archaeological area of Locri Epizephyrii (Calabria, southern Italy) was chosen for this purpose. An unsurveyed rectangular area (31 × 26 m) was investigated with high-density ground-penetrating radar (GPR) and magnetic profiles. Several anomalous alignments, both compatible and oblique with respect to the orientation of the Greek-Roman city plan, were preliminarly observed in the geophysical results. The use of two different techniques allowed for comparison of anomalous areas, enhancing the likelihood of finding features of significance. Two archaeological soundings were later carried out in the areas showing the most peculiar geophysical anomalies. Several structures revealing the same orientation of the ancient city plan and belonging to at least two different building phases were unearthed from a depth of 15–25 cm below the ground surface. A systematic comparison between geophysical and archeological results was then carried out. In general, walls showing different construction typologies (opus testaceum, opus incertum or opus caementicium) were found to generate similar radar anomalies. Artifacts made with materials similar to the background sandy alluvial deposits were not identified by both geophysical techniques, as in the case of an unearthed channel bank, made of local sandstone blocks. GPR was globally observed to detect buried structures better than the magnetic method, probably due to background geological variables linked to the presence of Fe-rich minerals within the background sediments, generating noisier and scattered magnetic gradient maps
Glacier thickness modelling and monitoring with geophysical data constraints: A case study on the Indren Glacier (NW Italy)
Full text linkThe ongoing global temperature increase has accelerated the mass loss of glaciers worldwide, with Italian alpine glaciers being particularly vulnerable due to their small size, complex geometries and exposition that implies a fast reaction to thermal and hydrological modifications. In such a frame, the Indren Glacier (Aosta Valley, north-western Italian Alps) provides a valid test site to check the thickness evolution over the last two decades (1999–2020), through an integrated approach combining historical data, on-site geophysical measurements, remote sensing surveys, modelling and temperature analysis. Using a 2018 helicopter-based photogrammetric survey and Ground Penetrating Radar (GPR) survey campaigns of 2020, we obtained new input data and constraints to build up an updated thickness model for the whole glacier through the Glacier Thickness Estimation algorithm (GlaTE). Ice thickness is indeed a key parameter to estimate the ice volume and use it as further input in evolutionary models forecasting future scenarios. As a part of this integrated approach, we also analysed remote sensing and temperature data, finding a major modification in the glacier conditions over the last decade. Further comparing these results with previous studies, we identified a significant decrease in ice thickness, and we confirmed the presence of an over-deepening in the glacier central widest part. This integrated methodology enhances our understanding of glacier dynamics and improves predictions of future changes, offering crucial insights for managing water resources and mitigating natural hazards in the alpine region
Case history : a magnetic and GPR prospection on a Roman rural villa in western Piedmont (Italy )
Full text linkTo explore an archaeological site in western Piedmont we proceed to a multimethod survey using fast methods and taking also into account the information achievable after a 2D or 3D data processing and/or rendering. This choice restricted the methodologies to magnetic and GPR prospecting. The non contact resistance imaging, in our opinion, still gives too smeared results even if indicative of resistivity anomalies. We selected the magnetic prospecting because of the remarkable size of some of the walls actually excavated even if, as we explain in the geological context, the probability of collecting a significant amount of noise was hig
Rockfall protection embankments: insights into impact effects
No full textRockfall reinforced earth embankments (RPE) are widely adopted defence structures against rockfall, particularly effective for high-energetic or frequent block impacts. Existing design approaches often involve simplifications, as RPE resisting mechanisms during impact has been not yet completely investigated. This study investigates the RPE response at the impact through a series of FEM analyses. Geophysical and plate load tests on an existing RPE are used to calibrate the soil constitutive law of the numerical model. The results of the huge campaign of sensitivity analyses, herein presented, allow to determine the mechanical and geometrical parameters most affecting the structural behaviour
Ambient Seismic Noise and Microseismicity Monitoring of Periglacial Bodies: A Case Study on the Gran Sometta Rock Glacier (NW Italian Alps)
Full text linkAmbient seismic noise and microseismicity analyses are increasingly applied for the monitoring of landslides and natural hazards. These methodologies can offer a valuable monitoring tool also for glacial and periglacial bodies, to understand the internal processes driven by external modifications in air temperature and rainfall/snowfall regimes and to forecast possible melting-related hazards in the light of climate change adaptation. We applied the methods to an almost continuous year of data recorded by a network of four passive seismic stations deployed in the frontal portion of the Gran Sometta rock glacier (Aosta Valley, NW Italian Alps). The spectral analysis of ambient seismic noise revealed frequency peaks related to stratigraphic resonances inside the rock glacier. Although the resonance frequency related to the bedrock interface was constant over time, a second higher resonance frequency was identified as the effect of variations in the active layer thickness driven by external air temperature modifications at the daily and seasonal scales. Ambient seismic noise cross-correlation highlighted coherent shear wave velocity modifications inside the periglacial body. The microseismicity dataset extracted from the continuous ambient noise recordings was analyzed and clustered to further investigate the ongoing internal processes and gain insight into their source mechanism and location. The first cluster of events was found to be likely related to the basal movements of the rock glacier and to falls and slides of the debris material. The second cluster was possibly related to shallow ice and rock fracturing processes. The validation of the seismic results through simple models of the rock glacier physical and mechanical layering, the internal thermal regime and the surface displacements allowed for a comprehensive understanding of the rock glacier's reaction to the external conditions
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