- Home
- Conferences
- Conference Proceedings
- Conferences
Near Surface Geoscience 2015 - 21st European Meeting of Environmental and Engineering Geophysics
- Conference date: September 6-10, 2015
- Location: Turin, Italy
- Published: 06 September 2015
1 - 20 of 164 results
-
-
A Multidisciplinary Hydrogeophysical Approach Applied to the Chalk Aquifer Using MRS (North of France)
More LessFor several years LaSalle Beauvais has regularly carried out hydrogeological and hydrogeophysical measurements in order to characterize the chalk aquifer in the vicinity of Beauvais (Picardie, France), in terms of geometry, behavior and development (Zouhri and Lutz, 2010). A multidisciplinary approach has been chosen: piezometric and meteorological measurements, near surface geophysics measurements (electrical resistivity tomography, seismic refraction…), logging (gamma-ray, water conductivity, temperature), and since June 2014: Magnetic Resonance Sounding. The main hydrogeophysical results obtained on the experimental site of LaSalle Beauvais are displayed in order to show how geophysics methods can improve the hydrogeological knowledge. We insist in particular on the results of Magnetic Resonance Soundings. This method, little used in France because of its susceptibility to electromagnetic noise, allows us to estimate the water content, the permeability and the transmissivity. All of these results, which will be complemented by pumping tests and water samples study in the future, will be of great interest for the water management in the Beauvais area.
-
-
-
Density Estimation Using Muon Imaging
Authors L.A. Preston, N.D. Bonal, D.J. Dorsey, D. Schwellenbach, W. Dreesen and J.A. GreenSummaryMuons are subatomic particles capable of penetrating the earth’s crust several kilometers. Muons have been used to image the Pyramid of Khafre of Giza, various volcanoes, and smaller targets like cargo. For objects like a volcano, the detector is placed at the volcano’s base and muon fluxes for paths through the volcano are recorded for many days to weeks.
-
-
-
Geophysical Imaging at the U.S. Critical Zone Observatories
Authors W.S. Holbrook, B. Carr, J. St. Clair and J. HayesSummaryOver the past two years, the Wyoming Center for Environmental Hydrology and Geophysics (WyCEHG) has imaged the subsurface at five CZO’s: Calhoun, Boulder Creek, Eel River, Reynolds Creek, and Southern Sierra. Techniques applied include seismic refraction, electrical resistivity, downhole logging, ground-penetrating radar, magnetic gradiometry, EMI, and surface NMR. We will present results from these sites.
-
-
-
Advances in the Application of Thermal Logging Techniques for Hydro-physical Characterization of Flow through Fractured Rock
More LessSummaryThe use of thermal techniques for identifying groundwater flow in fractured rock is experiencing a revitalization as a result of both advances in sensors and synergistic developments of other technologies. Multiple sensors with resolution approaching 0.001 C8 are combined to measure an orientated temperature field in the thermal vector probe (TVP).
-
-
-
Chargeability from Airborne TDEM Data - Model Studies and Field Examples
More LessSummaryElectrical chargeability has been observed in time-domain EM data for many years, but mostly as a curiosity or considered to be interference, rather than a useful geophysical measurement.
-
-
-
Spectral Analysis and Correlation of Ambient Seismic Noise. The Case Study of Madonna del Sasso (NW Italy)
Authors C. Colombero, L. Baillet, C. Comina, A. Helmstetter, D. Jongmans, E. Larose, J. Valentin and S. VinciguerraSummaryAmbient vibrations recorded on potentially-unstable rock slopes show that the temporal variations in the spectral content and in the correlation of seismic noise can be related to both reversible and irreversible changes within the rock mass. In this work, we analyzed the seismic recordings acquired at the potentiallyunstable granitic cliff of Madonna del Sasso (NW Italy) from October 2013 to November 2014.
The spectral content of noise systematically highlighted clear energy peaks at specific frequencies on the most unstable sector, interpreted as resonant frequencies of the investigated volume. Horizontal ground motion at the fundamental frequency was moreover found to be orthogonal to the main fractures observed at the site and consequently parallel to the potential direction of collapse. Cross-correlation was computed between the recordings of the sensors placed in the prone-to-fall compartment and a stable reference station.
Both the temporal variations of the resonant frequencies and the results of cross-correlation showed seasonal reversible variations related to temperature fluctuations. No irreversible changes, resulting from damage processes within the rock mass, were detected during the monitored period.
-
-
-
Microseismic Monitoring of an Unstable Rock Face - Preliminary Signal Classification
Authors D. Arosio, L. Zanzi, L. Longoni and M. PapiniSummaryWe analyse signals collected by a microseismic monitoring network installed on an unstable rock face threatening the city of Lecco, in the North of Italy. We propose a classification process based on parameters computed in both time and frequency domains able to identify events possibly related to microseismic activity within the unstable rock mass and discard unwanted signals caused by meteorological conditions or other sources of noise. Our classification routine seems to be robust and the preliminary outcomes are in agreement with the findings reported in previous studies. We believe that further investigations together with the integration with a localization process of the significant microseismic events will improve our approach.
-
-
-
Seismic and Resistivity Monitoring of Pont Bourquin Landslide in Switzerland
Authors S.R Carrière, G. Bièvre, E. Larose, D. Jongmans, T. Lebourg, L. Baron and M. JaboyedoffSummaryLandslides are natural and complex phenomena which can be encountered all over the world. They affect all types of geological formations and present a large variety of size, morphology and displacements rates. Among these phenomena, landslides in clay-rich formations are particularly complex due to the still unpredictable acceleration and fluidization that characterize them. In order to better understand this solid-fluid transition, the Pont Bourquin landslide in Switzerland has been continuously monitored with at least two vertical seismic sensors since the beginning of 2010, and 36 electrodes since the beginning of 2014 to assess the resistivity changes at different locations of the landslide. Relative velocities changes processed from ambient noise correlation show seasonal fluctuations between −2 and +2 % along the years. Only one drop of more than 7% was observed in summer 2010 preceding a major earthflow, showing that daily dV/V processing could be used as a precursor signal for landslide activation. Resistivity measurements show that certain parts of the landslide undergo strong electrical changes for which the causes are not yet determined. Because of the structural complexity of the landslide, further studies are requested to better understand the coupling between geophysical soil properties and environmental parameters.
-
-
-
Role of Fracturing on Seismic Noise Measurements - The Case of the Bory Crater (La Réunion Island)
Authors P. Bottelin, J. Valentin, D. Jongmans, L. Baillet, F. Donze, O. Brenguier and A. MangeneySummaryIn recent years, ambient seismic noise measurements have significantly developed in gravitational hazard assessment for both investigation and monitoring purposes. The wide frequency range allows ambient vibrations to be applied for investigating geological and civil engineering structures in a great variety of sizes, from the lithospheric or crust scale to a few m-thick landslide and rock column or buildings. On landslide sites, several studies revealed significant spectral amplification at given frequency and polarization of the wave-field in the direction of maximum slope displacement. They show that different characteristics (resonant frequencies, polarization, and spectral amplification) could be used from the spectral analysis of the ambient motion or from spectral ratios for characterizing landslides.
This study aims to study a prone-to-fall column located at the top of a basaltic cliff in the Bory Crater (Réunion Island). Seismic prospecting profiles were performed on the plateau to characterize the basaltic lava deposits and the ambient seismic noise was measured using 3C sensors located on the column and at several distances from the cliff. The studied showed a clear resonance effect due to the column vibration, as well as larger site effect which could be related to the fracturing in the Bory crater.
-
-
-
On the Use of ERT and AEM Resistivities for a Tunnel Pre-investigation
Authors S. Bazin, H. Anschütz, A.K. Lysdahl, J. Scheibz and A. A. PfaffhuberSummaryWe have investigated the applicability of resistivity derived either from surface electrical resistivity tomography (ERT) or airborne electromagnetic (AEM) surveys to a tunnel pre-investigation. We have exploited resistivity models to map the extent of toxic black shale along a tunnel alignment in central Norway. The resistivity models acquired before excavation and supported by laboratory measurements enabled us to map geological layers that are in agreement with the rock types subsequently observed from drillings and geological logging during tunneling. Our results highlight the potential of AEM surveys for such tunnel pre-investigations.
-
-
-
A Study of Misfit Topography towards Waveform Inversion for Prediction Ahead of Underground Tunnel
Authors L.T. Nguyen and T. NestorovicSummaryThis work presents a synthetic study of misfit topography towards identification of geological structure ahead of the underground tunnel by waveform inversion. Simulation of viscoelastic waves is performed by the spectral element method implemented in SPECFEM2D package. By modeling a simple 2-dimensional underground tunnel model with a dip geological interface ahead of the tunnel face, we construct the misfit error landscapes with respect to geometric parameters defining the dip layer interface. As a result it is found that the misfit topography is very multimodal and therefore finding the true model by waveform inversion is likely to be very challenging. However, the choice of misfit definition, for example by using the envelope misfit, can help ease the toughness of misfit topography and facilitate the inversion task.
-
-
-
Statistical Soil Type Estimation Based on Cross-plots of S-wave Velocity and Resistivity in Japanese Levees
Authors K. Hayashi, T. Inazaki, K. Kitao and T. KitaSummarySoil type of levee body and foundation are statistically estimated using cross-plots of S-wave velocity (Vs) and resistivity in Japanese levees. The Vs and the resistivity are collected from surface wave methods and resistivity methods. Total survey line length of the geophysical methods is about 600 km on 37 rivers in Japan. The blow counts and soil types are collected from about 400 boring logs carried out on geophysical survey lines. Vs and resistivity at the depth of the blow counts were extracted from geophysical sections. The total number of extracted data is about 4000. The data is grouped in levee body and foundation. A polynomial approximation was used to estimate the soil type from Vs and resistivity. Coefficients of equations are optimized by a least squares method. Accuracy of estimation was statistically evaluated by comparing estimated and actual soil parameters. Soil type sections were calculated from Vs and resistivity sections using the polynomial approximations.
-
-
-
Ambiesta Dam - Geophysical Survey to Define the Cracks Patterns inside the Structure
Authors A. Masera, D. Donnaruma and D. MilaniSummaryThe paper describes the investigation using sonic tomography, performed on the Ambiesta dam (Italy) and aimed to characterize and identify the concrete cracking patterns inside the dam body, starting from the surevy of cracks visible on the downstream face.
The investigation had to define the depth of the cracks patterns and define the concrete caractheristics in the area affected by the cracks compared to healthy areas or free from cracks.
-
-
-
GPR Assessment of Columns in the Pavilions and the Church of the Modernista Building Sant Pau Hospital, in Barcelona
Authors S. Santos-Assunçao, R. Gonzalez-Drigo and V. Perez GraciaSummaryThe work presents a case study applied to the analysis of columns in cultural heritage. The GPR assessment of columns in three different places of a Modernista set of buildings allows determining the differences in constructive solutions. The study of the church denotes that the columns are masonry structures with four metallic reinforcements along the shaft. The analysis carried out in the pavilions highlights differences between two types of masonry columns: some of them are built with regular arrangement of bricks and seem to be solid structures; others have a metallic pipe (a rain drainage tube) in the centre of the structure, and the inner elements are most likely portions of bricks with a shape similar to a triangles.
-
-
-
Photogrammetry and 3-D Ultrasonic Tomography to Estimate the Integrity of Two Sculptures of the Egyptian Museum of Turin
Authors L. Sambuelli, G. Böhm, C. Colombero and A. FilipelloSummaryWe 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.
-
-
-
High Resolution Geophysical and Topographical Surveys for the Characterisation of Fumane Cave Prehistoric Site, Italy
Authors M. Obradovic, N. Abu Zeid, S. Bignardi, M. Bolognesi, M. Peresani, P. Russo and G. SantaratoSummarySmall scale prehistoric archaeological sites, such as the Fumane cave, located north of Verona city in north Italy, poses a lot of challenges both to archaeologists and geophysicists. The cave is considered as one of the most important Middle and upper Prehistoric sites of Europe, discovered in 1884. It contains a well-preserved and impressive stratigraphic sequence of more than 12m thick where human activity remains are accumulated. In this work, we applied high resolution geoelectrical resistivity tomography and seismic passive geophysical methods to investigate, on one hand, the electrical properties of the shallowest part of the deposit, where, a number of medium to low resistivity anomalies were localised. On the other, a test using microtremors provide evidences on the probable maximum thickness of the deposit (4–5 m). In addition a high resolution and georeferenced laser scanner survey was carried out so as to have an high resolution topographic model that shall be used as a container to allocate in 3D the position of the already achieved findings as well as the geophysical results. This shall constitute the first step for the planning of a smart protocol for results conservation and dissemination both for cultural and scientific interests.
-
-
-
Archaeogeophysical Experiments in the Large Scale Laboratory
Authors F. Perciante, L. Capozzoli, V. Giampaolo, R. Luongo and E. RizzoSummaryThe ArchaeoGeophysical techniques are based on the investigation of buried cultural structures and surrounding materials in the archaeological framework. Unfortunately, the geophysical contrast between archaeological features and surrounding soils sometimes are difficult to define due to problems of sensitivity and resolution both related on the characteristic of the subsoil and the geophysical methods. An archaeological experimental activity has been performed in the Hydrogeosite laboratory, a full large scale controlled site consisting on a pool shape structures of 230m3 where archaeological remains have been installed. The laboratory experiment was performed to assess of the capability of EM geophysical techniques to detect archaeological remains placed in the humid/saturated subsoil. The archaeological test site was characterized by remains of Roman times (walls, tombs, roads, harbour, etc.) covered by sediments. In order to simulate lacustrine and wetland condition and to simulate extreme events (for example underwater landslide, fast natural erosion coast, etc.) the phreatic level was varied and various acquisitions for the different scenarios were performed. The integration of electric and electromagnetic data in that conditions allowed us to overcome the limits of each technique in terms of resolution and depth. Moreover, the experiment highlight the uncertainties related on the interpretation of geophysical analysis.
-
-
-
Quality Assurance of Jet Grouting Columns Using Seismic Methods
Authors E. Niederleithinger, J.C. Galindo Guerreros, S. Mackens and T. FechnerSummarySealing and strengthening of the subsoil by injection is a major issue in the field of geotechnical engineering. This involves also jet grouting, which allows creating columns of grouted soil by eroding and mixing the in-situ soil with a thin cement suspension. A general difficulty of this method is to predict the column diameter and its material strength. Here, we present two-dimensional finite-difference numerical simulation results of a promising non-destructive quality assurance testing tool to evaluate the diameter of jet grout columns. This approach incorporates crosshole and downhole seismic measurements. Preliminary tests showed that this tool is applicable under real site conditions.
-
-
-
Sensitivity of Seismo-electric Waveforms and Electric Noise to Electrode Configuration
Authors M.S. Devi, D.R. Dietrich and D. R. GaramboisSummaryThe seismo-electric exploration method aims to analyse the electromagnetic signals generated when seismic waves excite, and then propagate through a fluid-filled porous or fractured medium. Seismo-electric signals are obtained by firing a seismic source and recording the resulting electric fields. Such experiments usually allow one to detect the dominant contributions of the seismo-electric response, namely the electric signature of seismic surface waves and guided waves propagating in the near surface. Of more interest are the electromagnetic waves generated at depth when seismic waves cross an interface. These signals are much more difficult to discern due to their very weak amplitudes and because of the ubiquitous man-made electric noise that dominates the records. As a workaround, we investigate here the possibilities offered by multi-electrode arrays to enhance the EM interface response and mitigate the power line noise at the same time.
-