- Home
- Conferences
- Conference Proceedings
- Conferences
Near Surface 2006 - 12th EAGE European Meeting of Environmental and Engineering Geophysics
- Conference date: 04 Sep 2006 - 06 Sep 2006
- Location: Helsinki, Finland
- ISBN: 978-90-73781-62-7
- Published: 04 September 2006
1 - 50 of 142 results
-
-
Why Not X in Airborne TEM?
Authors E. Auken, A. V. Christiansen and K. SørensenWe describe the challenges for the realization of a transient EM (TEM) system capable of measuring both the z- and x-components. This involves significant changes to instrumentation as well as to the processing and inversion algorithms.
Geophysical mapping of groundwater resources using TEM involves both delineation of the aquifer structure and the aquifer protection. The demands for the instrumentation and the processing algorithms are quite different for the two tasks. Structural mapping requires large depth penetration and thereby a large transmitter moment while aquifer protection mapping requires early time measurements and extremely accurate determination of the system transfer function. Furthermore, the inversion software must be capable of modelling this system transfer function.
For an airborne TEM system systematic analysis of the resolution capabilities of relatively thin low resistive layers in the upper 30 - 50 m of the subsurface has shown that the resolution is enhanced if not only the transient z-component but also the transient x-component of the induced fields in the Earth is measured and included in the inversion.
The abstract will describe and discuss three major challenges related to the inclusion of the x-component in an airborne TEM system.
-
-
-
The New 4-Frequency Airborne EM System of JAC
Authors M. Kurimo, I. Suppala, H. Leväniemi and M. LahtiGeological Survey of Finland (GTK) and British Geological Survey (BGS) have jointly (JAC) constructed a new, 4-frequency EM unit installed in a fixed-wing aircraft. The system follows the technique of the previous dual frequency unit of GTK. The frequence range is now from 0,9 to 25 kHz. The four separate coils are installed inside the pods situated at the wing-tips, the separation between transmitter and receiver coils being 21.4 m. The system sensitivity is wide, covering well geological and environmental targets, and the lowest frequency enhances the depth penetration.
This paper describes the technical characteristics of the new system: specifications and noise level, and analyses the half space model responses. A test area survey was performed to find out the possibilities to utilise the data in interpretation. A 3D model based on systematic 1D inversion was compiled successfully.
-
-
-
Laterally Constrained Inversion of Fixed-Wing Frequency-Domain AEM Data
Authors E. Tartaras and D. BeamishNew high-resolution airborne geophysical surveys of the UK, undertaken with the system developed under the Joint Airborne-geoscience Capability programme, established between the Geological Survey of Finland and the British Geological Survey, will provide large 4-frequency airborne electromagnetic data sets. These data sets will be used to characterise the conductivity distribution of the subsurface for environmental and exploration purposes. To invert these large data sets in a fast and robust manner we have developed “LC1DINV”, a laterally constrained one-dimensional inversion algorithm. This algorithm inverts simultaneously for all observation points along a profile and regularises the inverse problem by requiring that differences between model parameters at adjacent points be small. We use the conjugate gradient method for minimising the data misfit subject to the lateral constraints and a priori model terms. We have inverted 4-frequency data obtained over Suurpelto, a test area in southern Finland, characterised by conductive clays overlying a highly resistive granitic shield. The results show that LC1DINV can successfully locate the depth extent and variations of the clays. Comparison of these results with those obtained with two other types of inversion shows that LC1DINV produces well-defined layer boundaries and laterally smooth cross-sections.
-
-
-
Laterally Constrained 1D Inversion of Airborne Electromagnetic Data
Authors M. T. Pirttijärvi and J. LerssiThe transformation of airborne electromagnetic (AEM) data into apparent resisitivity and depth is traditionally made separately for each measurement point and does not take into account the neighbouring data or model values or multiple frequencies. Laterally constrained inversion, where the model roughness is minimized together with the data error using a 1-D layered earth model, provides an easy and fast method to transform multi-frequency AEM data into a physically more meaningful form. The method is based on linearised inversion, singular value decomposition and adaptive damping together with Occam type constraining for model roughness. The new inversion method is implemented in the AEMINV program program, the graphical user interface of which is based on the DISLIN graphics library. Thus, it can be compiled and run on a variety of computer platforms without major modifications. The inversion method was found stable and computationally efficient. Because the model is one-dimensional, the results show apparent resistivity and depth although the inversion yields 2-D resistivity pseudo-sections. The AEM inversion using a two-layer model, however, gives a possibility to map separately the overburden conductance and basement resisitivity.
-
-
-
Post-Tsunami Helicopter-Borne Electromagnetics Along the Coasts of Aceh, Indonesia
Authors B. Siemon, A. Steuer, U. Meyer and H. J. RehliAfter the earthquake and the tsunami-event on December 26, 2004, the Indonesian and German governments decided to set up a project that was dedicated to re-install the public life of the people in the coastal region of Aceh Province, Indonesia. As the tsunami waves caused large scale coastal salt-water intrusions and destroyed thousands of shallow drinking water wells, the focal point was the water assessment in coastal areas of Aceh about nine months after the tsunami.
The target areas are: Banda Aceh / Aceh Besar, the west coast between the towns of Calang (Aceh Jaya) and Meulaboh (Aceh Barat), and Sigli on the north-east coast. A helicopter-borne survey including five-frequency electromagnetics (HEM), magnetics and gamma-ray spectrometry was conducted by the BGR airborne group from August to October 2005. The northernmost survey area, Banda Aceh / Aceh Besar, comprises a 20 km by 50 km wide area that was surveyed within four weeks.
The HEM survey revealed coastal saltwater occurrences caused by the tsunami, deep saltwater occurrences up to several kilometres inland, and several potential fresh-water occurrences. Several requests for information on the geological/hydrogeological situation at sites for planned water wells were successfully evaluated.
-
-
-
The Tellus Airborne Geophysical Survey of Northern Ireland
Authors D. Beamish and H. LeväniemiThis paper describes an airborne geophysical survey of Northern Ireland that is being conducted over a two year period. Measurements from a fixed-wing aircraft operating at 56 m include magnetic (gradiometer), radiometric and frequency-domain electromagnetic. The survey will complete over 80,000 line-km of coverage in the summer of 2006. The Phase 1 data, described here, comprise ~47,000 line-km obtained across the western and central areas of the province. The nature of acquiring geophysical data, at high resolution (200 m line spacing) in populated areas is distinct from that of other exploration contexts. The survey is being coordinated and conducted alongside a high public profile. The initial Phase 1 Tellus survey results have exceeded expectations. They have excited the interest of the planning, mineral and environmental communities.
-
-
-
Semi-Automatic Approach to Deculture High Resolution Airborne Data
Authors M. Lahti, R. J. Cuss and A. DonaldThe problem of cultural noise places a severe limitation on the effectiveness of high-resolution airborne magnetic surveys. This paper presents a semi-automatic deculturing approach to enhance data from Northern Ireland surveyed in 2005. The high-resolution data (200m line spacing, 56 m flight elevation) acquired over this highly developed country is affected by cultural noise connected to various man-made sources potentially masking subtle geological information. The semi-automatic approach consists of two steps: 1) Automatic use of Pointer data to locate potential sources of cultural noise e.g. houses. 2) Manual refining of Pointer filtered data to clean remaining cultural noise and minimising geological distortion. The two-step approach allows a quick delivery of Pointer-filtered data where the level of cultural influence is significantly reduced. The final manual cleaning of remaining cultural noise is a slower process that results in high quality data with enhanced geological signature.
-
-
-
Kimberlite Exploration at Low Magnetic Latitudes. Case Study at Serra da Canastra, Brazil
Authors P. T. L. Menezes and M. D. M. GarciaAirborne magnetic data from Serra da Canastra diamondiferous province is used to identify possible kimberlite signatures. Serra da Canastra is located in the central portion of the Brazilian territory within a low magnetic latitude area.
The interpretation strategy was based on the joint analysis of analytic signal and Euler deconvolution. A selected kimberlite target should have a roughly circular analytical signal anomaly coincident with a depth (0 – 200 m) and structural (N=2)
constrained Euler solution. The proposed approach led to ecognition of previously known pipes and new targets were evidenced.
-
-
-
Geophysical Investigation of the Nasca Lines
Authors A. Weller, K. Hartsch, S. Rosas and G. ReppchenGeomagnetic mapping and electrical imaging are applied to investigate the soil structures in the vicinity of the geoglyphs in the Nasca desert (Peru) in comparison with areas of undisturbed soil in order to derive conclusions for a conservation of the lines. Both magnetic and geoelectrical method show significant anomalies caused by the lines but also structures of up to now unknown origin in the subsurface.
-
-
-
New Results on Comparison of Different GPR Systems and Antenna Configurations at the Roman Site Carnuntum
Authors S. Seren, A. Eder-Hinterleitner, P. Melichar and W. NeubauerAbstract
Extensive test measurements were carried out over the last 3 years to evaluate different GPR systems, configurations and post-processing methods for archaeological prospection (Seren et. al. 2005). A new antenna by manufacture GSSI, the increasing of the submitted power of two antennas and improvements in filtering and visualization give new comparably results.
-
-
-
2D and 3D Resistivity Tomography for the Detection of an Ancient Tunnel in Lavrion Area (Greece)
Authors C. Orfanos, G. Apostolopoulos and K. LeontarakisAt the archaeological site of Bertseko, in Laurion, the entrance of an ancient tunnel was found during archaeological excavations. After approximately 15 m the tunnel remains inaccessible – blocked with filled materials. 2d and 3d resistivity measurements were carried out in order to delineate the direction of the tunnel and to evaluate the effectiveness of resistivity imaging technique to detect such targets. Firstly, eight 2d resistivity profiles were carried out with the pole-pole array in a non-rectangular grid, in order to image a wider area, a greater depth, and to avoid several surface obstacles. Then the most promising area from the previous procedure was outlined and selected for analysis with 3d resistivity tomography (pole-dipole array) for better resolution. The field strategy adopted improves the delineation and the definition of the target and avoids the loss of valuable information with respect to the object under investigation. The integrated results from both 2d pole-pole and 3d pole-dipole profiles provide answers to archaeologist’s questions, delineate with great accuracy the direction of the tunnel and give rise to new aspects for the improvement of subsurface imaging and acquisition strategy.
-
-
-
Target Detection Using Multi-Sensor Geophysical Surveys - Examples from Archaeological Surveys
Authors I. A. Hill, P. R. Fuller and C. LeechMulti-sensor survey systems can perform archaeomagnetic surveys more cost effectively than existing techniques, while simultaneously providing a denser, precise dataset with the potential for extending interpretation beyond simple imaging. The full benefits of application of existing potential field interpretation techniques to such data is yet to be realised.
-
-
-
Combined Two-Dimensional Inversion of Four- and Three-Electrode Arrays Resistivity Data
More LessIn this paper, I suggest to use combined inversion of three- and four-electrode arrays data. Two-dimensional (2D) inversion results of Wenner (W), Schlumberger (S), Dipol-Dipol (DD), left- and right side pole-dipole (PD-L and PD-R) synthetic data and their combined inversion results are compared according to resolution and accuracy of the inverted models. Comparison results show that combined inversion of any two arrays data (eg. W+S, W+DD, PD-L+DD) sets give better resolution than the individual inversion of each corresponding arrays data set. However, inversion of PD-L, PD-R and and DD data sets jointly give better accuracy than the single use of any of these electrode arrays and combined inversion of any two electrode arrays.
-
-
-
EM Induction Frequency Sounding - Estimation of Penetration Depth
Authors E. V. Balkov, M. I. Epov, A. K. Mastein and Y. A. MansteinOne of the most important characteristics of any geophysical instrumentation is the penetration depth. Present paper is devoted to description of the approach for estimation of the penetration depth for frequency sounding method. The approach takes into account the accuracy of the instrumentation and geoelectrical model as well. It is more accurate than traditional one that based on skin depth estimation. The investigations are carried out for two types of target objects for EMI frequency sounding device EMS developed by authors.
-
-
-
Seismic – Acoustic Research on Identification of Some Archeological Buildings in the Submersible Zones
By A. SorinIn Romania, geophysical methods are normally used to estimate the distribution of cultural relics, before digging. Objects of archeological interest are usually located within a few meters of the surface.
Seismic –acoustic research was made with an specific equipment (“X-Star Full Spectrum Sub-bottom Profiler”)which works with frequency modulation in the range of 2-16 Hz. The vertical resolution of this system is better than 1 decimeter
-
-
-
Marine Resistivity Measurements for the Foundation of Lavrion Old (1888) French Bridge
Authors G. Apostolopoulos, G. Amolochitis and S. StamatakiMarine resistivity measurements can give valuable information for the sedimentation under the sea bottom if the latter is not too deep. The Schlumberger configuration is preferred with its more efficient signal-to-noise ratio. Pole-Pole can give information which is less accurate in horizontal layering but offers deeper detection and possible positioning of lateral inhomogeneities in the event of great resistivity contrasts.
The old (1888) iron “French Bridge” in Lavrion Port suffers from corrosion by seawater and displacements and needs protection with the plan all to be mounted in a new substructure with the less visible changes. The marine resistivity survey gives valuable information to the engineer like where the old foundation lays, where to position the geotechnical drillings for additional information and outlines the environment of the structure to be built for the protection of the bridge.
-
-
-
Gravity Survey in the Study of Vulnerability of Old Town
More LessGravity prospecting in urban areas can make possible to define vulnerability maps of territory, which are very useful in prevision and prevention of buildings crash risk especially in old town.
In this paper we show the results of two studies carried out to determine the shallow subsoil properties of two historical sites in Sardinia (Italy) by means the implementation of densities micro zoning map.
-
-
-
Magnetic Properties of Archaeological Building Materials from Egypt
Authors A. Weller and A. El-BassionyThe magnetic properties of the building material are compared with the parameters of the embedding soil. The X-ray diffraction measurements performed on the selected samples had shown a higher magnetite content in the mud-brick samples compared to the low content in the soil samples. The measurements of the magnetic volume susceptibility for the selected samples had shown a measurable contrast between the mud-brick samples and the soil samples in Saqqara and Qantir.
-
-
-
First Multi Beam and High Resolution Reflection Seismics Survey on the Tiber River Lower Course
Authors L. Orlando, M. Bernabini, A. Bosman, F. Chiocci and L. MacelloniAn integrated geophysical survey was carried out with the aim to investigate hydrodynamics, sedimentology, stratigraphy, pollution, archaeology and navigability of Tiber River (central Italy) lower course. Multibeam, side scan sonar and seismic reflection (Sparker and Pinger sources) data were acquired for a length of 80 km. The accurate location of the survey and the special processing used for the multibeam data gave us a digital elevation model of the river bed with a maximum resolution (in places) of 0.2 m.
-
-
-
Focused Inversion of Gradient Magnetic Data from Saqqara North Cemetery, Egypt
Authors A. Weller and A. El-BassionyInversion of magnetic gradient data for archaeological purposes is performed using a focusing functional. The focused inversion of real magnetic gradient data from Saqqara proves to be successful by using the Minimum Gradient Support as a focusing tool. Information about the susceptibility contrast between the archaeological structures and the surrounding soil is found to be critical for the reliability of the inversion.
-
-
-
First Results from Thermal Tomography in the Study of Wall Structures and Archaeological Layers
Authors C. Piga, G. Ranieri and R. DeianaMasonry walls, especially those of historic buildings, are often difficult to investigate. The current approach consists of analysing small portions of the structure. The techniques employed are often invasive and in any case incapable of providing a complete picture of the variety of problems to be solved. The aim of this work is to test the effectiveness and feasibility of thermal methods suitable for assessing the conditions of masonry.
Different physical models that mimics real conditions has been designed for this purpose. A number of anomalous elements were introduced in the models, to simulate the heterogeneity of the structure.
The same method has been applied in the analysis of thermal imaging to try to reconstruct buried walls. A quasi-real scale model has been constructed also in this case.
-
-
-
High-Resolution Seismic Reflection to Identify Areas with Subsidence Potential beneath U.S. 50 Highway in Eastern Reno County, Kansas
By R. D. MillerHigh-resolution seismic reflections were used to map the upper 200 m along an approximately 22 km stretch of U.S. 50 highway in Reno County, Kansas, where natural and anthropogenic salt dissolution is known to threaten ground stability. Surface subsidence in this part of Kansas can range from gradual (cm per year) to catastrophic (meter per second), representing a significant risk to public safety. The high signal-to-noise ratio and resolution of these seismic reflection data allowed detection, delineation, and evaluation of several abnormalities in the rock salt layer and overlying Permian sediments. Locations were identified where failure and associated episodes of material collapse into voids left after periodic and localized leaching of the 125 m deep, 40 m thick Permian Hutchinson Salt member were evident. Anhydrite and shale layers several meters thick within the salt are uniquely distinguishable and appear continuous for distances of several kilometers. Over a dozen unique features potentially related to subsidence risk were identified.
-
-
-
Applicability and Limitations of Impact Echo in Bridge Deck Condition Monitoring
Authors P. Shokouhi, N. Gucunski and A. MaherA010 Applicability and Limitations of Impact Echo in Bridge Deck Condition Monitoring P. Shokouhi * (The University of Texas at El Paso (UTEP)) N. Gucunski (Rutgers University) & A. Maher (Rutgers University) SUMMARY Near Surface 2006 — Helsinki Finland 4 - 6 September 2006 One of the most common problems in concrete bridge decks is a corrosion-induced deck delamination. A number of nondestructive testing (NDT) techniques have been utilized to map delaminated zones in concrete bridge decks (Scott et al. 2003). Impact echo (IE) an ultrasonic seismic method has proved successful in detection of delaminations in concrete bridge decks at
-
-
-
Target Prioritization in TEM Surveys for Sub-Surface UXO Investigations Using Response Amplitude, Decay Curve Slope, Signal to Noise Ratio, and Spatia
Authors D. Hall, S. MacInnes and J. DickersonTo reduce the number of false-positives in identifying UXOs and related debris for an ongoing Site Investigation, a target prioritization routine was developed based on the likelihood of a metallic source. Numerous parameters were evaluated statistically using over 2000 existing intrusive investigation results. Those showing the best ability to discriminate between metallic and non-metallic sources were incorporated into the scheme, including peak amplitude response, power-law decay slope, signal to noise ratio, and spatial match filter response. Parameters were assigned increasing numeric values based on likelihood of a metallic source, and summed to produce a target rank. Subsequent application to over 6000 new intrusive investigations revealed that the highest ranked 25% of targets were nearly five times more likely to yield a metallic source when investigated than the lowest ranked 25%. These results show that target selection routines in UXO investigations would benefit from using more parameters than just magnitude response, allowing more aggressive target identification and reduced costs by lowering the number of false positives that are investigated. Proposed refinements may further increase predictive capabilities.
-
-
-
Advancements in 3D Subsurface Modeling Using Refraction Data
More LessRecent advancements in refraction data analysis have increased the ability to image geologic features, provide better presentation, and offer additional benefits from refraction results. The end product from a refraction investigation can be either a 2D image or a full 3D model, as presented here. Full 3D earth models can be used for many purposes after the geophysical survey is complete. That is, subsurface physical property data in 3D model space permits site assessment from a new perspective. For example: structural loading, seismic loading, or construction excavation requirements can be evaluated using 3D model results.
This paper presents an advanced approach to refraction data processing, presentation, and visualization, using the "Geostructural Analysis Package" (GAP). GAP incorporates several numerical modeling processes: discrete element method, particle flow code, finite differencing, and the material point method. These four numerical modeling methods have been combined and optimized for seismic applications. GAP is an innovative tool that allows better data analysis and presentation that can be used to produce 3D volumetric models for further site analysis. A set of model results from a case history are presented to demonstrate the benefit of processing refraction data using this new approach. GAP represents the newest advancement in subsurface modeling using engineering-scale seismic data.
-
-
-
Using Borehole Radar to Image a Pothole in the Merensky Platinum Orebody
By P. du PisaniThe Merensky orebody (reef) in South Africa is one of the world's most important platinum resources. Potholes (slumps) in the Merensky Reef lead to significant mining losses. This paper describes for the first time how borehole radar can be used to image potholes in the Merensky Reef. Three dimensional visualization of the borehole radar data is used to delineate these structures and to improve the geological model ahead of mining.
-
-
-
Crosshole Radiowave Imaging (RIM) at Eurajoki Olkiluoto, Finland
Authors E. Heikkinen, A. Korpisalo, T. Jokinen, T. Zhienbaev, A. Shuval-Sergeev, N. Popov and T. AhokasCrosshole radiowave imaging survey was conducted late in 2005 at Eurajoki Olkiluoto in Finland. Work belongs to site characterization process for spent nuclear fuel disposal into Finnish bedrock, which is run by Posiva Ltd. Crosshole radiowave imaging (RIM) was performed as a joint operation of Geological Survey of Finland and FGUNPP Geologorazvedka from Russia, using FARA-MCH tool. Pöyry Environment reviewed the results and compared the material to existing background information. The field work performed successfully between two borehole pairs at surface collar distances of 250-300 m. Recorded amplitude data were processed to resistivity images using crosshole tomographic reconstruction. The results prove that the method can be used in 100-400 m scale between boreholes to delineate and follow sulphide-bearing horizons, which are controlled by ductile and brittle geological processes in the site. Obtained results indicate that the location and geometry of resistive and conductive units in bedrock correlate rather well with data from geological mapping and geophysical logging from boreholes. The obtained projected geometry correlates also rather well with one subset of seismic 3-D reflections, and with geophysical electrical and electromagnetic results from the site.
-
-
-
Monitoring Leachate Levels in Landfill Sites Using Automated Time-Lapse Electrical Resistivity Tomography (ALERT)
Authors O. Kuras, R. D. Ogilvy, J. Pritchard, P. I. Meldrum, J. E. Chambers, P. B. Wilkinson and D. LalaAutomated time-Lapse Electrical Resistivity Tomography (ALERT) is a concept that aims to provide tomographic images of landfill sites at regular intervals or on demand. The British Geological Survey has developed an ALERT system specifically for the deployment on landfills and has undertaken a research programme focussing on leachate monitoring techniques based on ERT. Simple scale experiments demonstrate the capabilities of the ALERT technique to accurately monitor liquid levels in a porous medium between wells. ALERT data provide additional control and information about inter-well properties and processes, thus contributing to an improved understanding of landfill hydrology.
-
-
-
Combined Monte Carlo and Gradient Procedures Used to Optimized Solution of the Comprehensive Interpretation of Well Logs
Authors U. Woznicka, J. A. Jarzyna and A. CichyThe comprehensive interpretation of well logs is a mathematical task on a solution of a set of equations. The number of equations is determined by the number of the logs and conditions determining boundary and geological requirements. The common methods (e.g. gradient method, GRAD) are limited to cases when one global minimum occurs in the examined range of variables. Only Monte Carlo method, MC, which consists on numerous solutions obtained by random sampling of possible variables can find the global minimum of the function when other local minima are present. The MC method is time consuming, especially, in application to the well logging interpretation when enormous number of points along the depth profile should be calculated. We propose a complex method of solution combining both MC and GRAD methods. The method has been applied to the Interlog application in the GeoWin system for processing and interpretation of well logs and the field example is presented in the paper. The results confirm that the combined MC-GRAD solutions can give more information than the simple GRAD solution. Presented approach can be treated as an additional tool, especially dedicated for log analysts, for solving a set of logs difficult to interpretation.
-
-
-
Correctness of the Comprehensive Interpretation of Well Logs Regarding to Geological Conditions and Calculation Methods
Authors J. A. Jarzyna and U. WoznickaA great amount of unknowns resulting from a complicated lithology and from many logs run in a borehole causes that a set of equations in the comprehensive interpretation is great and sometimes indeterminate. In real geological conditions we sometimes get solutions that are different from laboratory estimates of porosity or other parameters. Discrepancies between lab measurements and geological data on one side and results of the comprehensive interpretation of well logs on the other side were the direct reason to examine the method of optimization adopted for solution. The proposed mathematical solution in the form of combined Monte Carlo and Gradient methods works as a tool assuring interpreter that the solution is correct. The general results obtained from Interlog-GeoWin were compared to ULTRA and Petrolog systems and the agreement was satisfied.
-
-
-
Geoelectric Survey of Hydraulic Experiments at the German Deep Drilling Site KTB at KM-Scale
Authors D. Laass, E. Danckwardt, G. Petzold and R. VoigtOne of the major findings of the German Continental Deep Drilling Program was the evidence of free fluids down to a depth of nearly ten kilometres. Furthermore, a series of hydraulic experiments in the pilot borehole focused on the characterization of transport processes of fluids in crystalline crust were carried out. Because of the significant differences of the electrical conductivity between the investigated fluids (natural free saline fluids and artificially inserted fresh water), geoelectrical methods are qualified for a successful detection in the kilometre scale. The Fluid Pump Test (2002/03 – production of about 22,300 cubic metres of saline formation fluids) or the Fluid Injection Test (2004/05 – injection of about 84,600 cubic metres of fresh water) clearly indicate a decreasing respectively an increasing in electrical resistivity. Inhole-logs in the open hole section (3,850 m – 4,000 m) could give a first indication (very closed to the pilot borehole) of consequence of the producing of saline formation fluids respectively of the fluid inflow displaced by injected fresh water last year. Also in greater distances to the pilot borehole, the time course of the decreasing (2003) and of the increasing of the apparent resistivity (2005) could be measured by geoelectrical combined surface-hole-experiments.
-
-
-
Active and Passive Seismic at the Unstable Rock Slide of Åknes (Norway)
Authors I. Lecomte, M. Dietrich, M. Roth, O. Méric, C. Delarue and J. S. RonningThe unstable rock slope of Åknes, Western Norway, has been recently identified as a potential threat for people and infrastructure in the inner Storfjord system. The unstable part has an estimated total volume of 30 to 40 million m3 based on recent geological and geophysical mapping. It is moving with a mean rate of about 4 cm/year, but with a rate as high as 15 cm/year in some parts. Such rock slide, when hitting the water in the fjord, could generate a flood wave (tsunami) with severe consequences, as experienced in the past by the local population. During the 2005 field campaign, three seismic measurements/installations were made: 1) a refraction seismic experiment in the center of the slope to map a potential sliding plane, 2) a temporary installation of 10 seismic mini-arrays of 9 channels each for passive monitoring of seismic events and noise measurements, and 3) a permanent installation of a smaller-scale seismic network for long-time monitoring of the site with real-time data access.
-
-
-
2D Inversion of the First Field Data of a New Radiomagnetotelluric Device in the Frequency Range from 10 kHz to 1 MHz
Authors B. Tezkan, A. Saraev, V. Shuman, P. Georgescu and N. B. ChristensenIn the project RMT-monitoring funded by the European Union, a new radiomagnetotelluric device has been developed which can record time series of electric and magnetic fields in a wide frequency range from 10 kHz to 1 MHz. Transfer functions are determined by spectral analysis using a newly developed processing software. A workbench program has been developed in which the transfer functions are interpreted with conductivity models based on new inversion algorithms.
The developed tensor radiomagnetotelluric device was tested in the laboratory and then applied successfully in the field to several environmental and groundwater problems in Russia, Ukraine, Denmark, Romania, and Germany.
The observed transfer functions in the field are the first ones worldwide in the frequency above 250 kHz which leads to a better resolution of the shallow structure. The new device enables quick and efficient mapping of polluted areas and supports tensor measurements allowing a 2D or 3D interpretation of the field data.
-
-
-
High-Resolution S-Wave Reflection Survey in Urban Areas Using a Woven Belt Type Land Streamer
By T. InazakiHigh-resolution S-wave reflection surveying has been successfully conducted on the paved surface in large urban areas by means of a Land Streamer, which was originally developed by the author. The Land Streamer is featured by non-stretch woven belt which acts as a towing member but also as a module to mount geophone units. Whereas each geophone unit is placed on the paved surface through a metallic baseplate instead of firm planting to the ground, the Land Streamer tool provides comparatively clean data even on the pavement resistant to traffic noises. Consequently, the tool is capable of expanding the opportunity of S-wave reflection survey in the urban areas where the surface is mostly paved and cultural noise is considerably high. A series of high-resolution S-wave reflection surveys conducted at paved surfaces in large urban areas successfully delineated detailed structures of the surficial layers shallower than 60 m, and proved the wide availability of the tool to engineering, environmental applications, and earthquake disaster prevention.
-
-
-
Geophysical Surveys in Prospecting of the Granite Host Rock of a Planned Radioactive Waste Disposal Site in Hungary
Authors A. Gulyás, L. Vértesy, A. Madarasi and J. KissA great amount of geophysical work was involved in the programme of final disposal of low- and intermediate-level radioactive waste in Hungary. Among others wide spectrum of geoelectric-electromagnetic methods were applied from the early stages of the project. In this poster we present the results obtained in prospecting the internal structure of the granite body either outcropping in the deep valleys, or buried under 30-60 m thick Quaternary sediments. VLF, Slingram-EM and high-frequency magnetotelluric surveys were performed to extend the detailed but were scarce information of the borehole geoelectric measurements and obtain a spatial view about the resistiv-ity distribution of the granite body, to delineate conductive zones of as possible tectonic zones, blocks etc. Regional gravity, magnetic and magnetotelluric studies were performed to delineate the granite body and for marking out regional structural lines.
-
-
-
Geophysics in Constructing the Geological Model of Olkiluoto
Authors M. Paananen, T. Lehtonen and T. AhokasThe paper presents some geophysical results that have been useful in constructing the geological model of Olkiluoto. Interpretation of wide-band EM soundings, HLEM, charged potential and single-hole measurements revealed several sulphide-rich conductive zones. These zones often appear to control also the brittle deformation zones.
-
-
-
Investigation of the EDZ Using High-Resolution GPR with Modulating Frequency
Authors Y. Suyama, M. Toida, K. Masumoto and S. TakeuchiThe EDZ (Excavation Damage or Disturbed Zone) is considered to be a fast transport pathway and provides a boundary condition for transport in bentonite buffers in groundwater scenarios for the geological disposal of radioactive waste. The distribution of the EDZ obtained through in-situ measurements, is important for safety assessments. High-resolution Ground Penetrating Radar (HGPR) with modulating frequency functions as a wide-angle measurement technique. It is one of the advanced techniques that can be used to investigate the EDZ of a radioactive waste disposal tunnel. Verification tests of the HGPR were carried out using a model and in-situ condition in the gallery of Tono mine in central Japan, where comprehensive techniques for investigation, analysis and assessment of the deep geological environment had been developed. In summary, it is shown that the investigation technique was able to detect underground structures with a resolution of less than 0.1m.
-
-
-
Quality Control and Validation of Detailed Logging Data from Slim Boreholes
Authors E. J. Heikkinen, T. Lehtimäki and T. AhokasBorehole geophysical logging data can provide a direct link between results of large scale geophysical methods and core sample analysis. Also the in situ measurement data will focus the measured response to actual location and to the specific lithology, or overprint of alteration or deformation. This way the logging data serves as unique means to explain and control the results from a large variety of different views and scales, ranging from airborne and ground level mapping to seismic reflection surveys and electromagnetic soundings. The actual parameter information used in model interpretations is only accessible by borehole methods. Further to this, the comparison of different parameters and geological background information can lead to better understanding of processes involved in the subsurface. The presentation deals with practices of quality control and validation of slim hole logging data using different geological and sampling control data. The work includes the sample controlled conversion of measurement data to meaningful physical properties, depth matching of the data to a very good location accuracy, and computing of derivative parameters. Example data set has been produced in site characterization project of Posiva for spent nuclear fuel geological disposal in Finland.
-
-
-
Geophysical Studies at the Suurpelto Construction Area
Authors T. K. T. Huotari, I. A. Suppala, H. T. Vanhala, T. Valjus, A. E. K. Ojala and J. P. PalmuIn this project geophysical, geological and geotechnical data has been collected from the Suurpelto construction site. The Suurpelto site is locating in the City of Espoo in southern Finland. The main aim of the studies is to investigate the geological history of the site and also use the data for constructional purposes. Airborne, ground as well as laboratory geophysical techniques have been used during this project. AEM measurement is fast method for outlining the highly conductive clay areas. 1D-inversion of 4-frequency AEM data was done using constrains from other Suurpelto datasets. More detailed conductivity structures were achieved from inverted ERT and ground EM data. The laboratory resistivity measurements revealed the highly conductive clays and less conductive gyttja clay sections from the drillhole samples. These sediments are the most difficult for constructional purposes.
-
-
-
Municipal Waste Dump Geophysical Investigation
Authors M. Bavusi, E. Rizzo, V. Lapenna and S. PiscitelliThe proposed work is about the geophysical survey applied in three Italian waste dump (Savoia di Lucania and Pallareta in Basilicata region, Novellara in Emilia-Romagna Region). The Basilicata landfill are provided of HDPI liner while in the other one a compacted clay stratum is present at the bottom. In each site we carried out active and passive geophysical techniques: electrical resistivity tomographies (ERT), induced polarisation (IP), self potential (SP) and magnetic methods. The ERTs, inverted by using the Res2DInv software, provided information about the geometry of the waste basins where an HDPI liner is present. The IP results show high chargeability nuclei into the refuse indicated the metallic garbage cumuli. The SP signal is negative into the basins and slightly positive in the surrounding area. Moreover, the SP data show strong spikes at the borders of the basins. The SP data of Novellara waste dump (clay stratum coating) show positive values inside the basins. The magnetic method evaluates the dispersion of metallic garbage close to the waste dumps. Finally, the different acquired data allow to sketch the lateral and buried geometry of the waste basins and to infer their leachate-tight, at least where the HDPI liner is present.
-
-
-
Electrical Resistivity Tomography (ERT) as a Tool for Monitoring Moisture Dy-namics in Soil Filled Containers
Authors O. Mohnke, K. Prokoph and U. YaramanciThe geophysical subproject of the multidisciplinary research group INTERURBAN (DFG 409), formed to investigate the water- and solutedynamics at urban locations with particular attention to spatial heterogeneity and biological transformation processes in the unsaturated zone, aims at the development of a noninvasive conception to map the water distribution and dynamics at small scales. Hydrophobic areas have a major impact for the transport of water and matter through preferential flow in soils. Soil animals, e.g. earthworms, modulate the composition of soil solutions in time and have a species-specific impact on the release pattern of nutrients and pollutants from plants and soil. To assess the possibilities and limitations of 3D ERT in the cm-dm range to monitor the long and short term dynamics of water repellent zones in the presence of soil fauna activity a feasibility study was carried out using soil filled mesocosms (MC) inoculated with earthworms. Results indicate a sufficiently high spatial resolution and sensitivity to reliably monitor in-situ changes of soil moisture on the relevant scales, Earthworm inoculated MC indicate a more homogenous decrease of resistivity throughout the MC whereas in the reference MC the changes are confined to the area below the irrigation zone.
-
-
-
Criteria of Gas Hazard Assessment in the Areas of Closed Mines of the Wałbrzych Coal District, Southwestern Poland
Authors H. Sechman, M. Dzieniewicz, M. J. Kotarba and A. KorusThe mine closures in the Wałbrzych Coal District, and particularly the cessation of drainage, resulted in the recovery of the groundwater table in Carboniferous multi-aquifer system which, in turn, intensified the flux of coalbed gases into the near-surface zone.
Surface geochemical surveys run in the years 1997-2001 and 2004-2005 in the Wałbrzych District demonstrated general increase in methane (up to maximum 49.6 vol. %) and carbon dioxide (up to maximum 17.4 vol. %) concentrations in soil gas samples collected at depth down to 2 m. The forced influx of methane and carbon dioxide into the near-surface zone measured with the modified, static chmaber method was up to 620 dm3/m2h i 330 dm3/m2h, respectively. Studies on coalbed methane and carbon dioxide flux to the near-surface zone supported by geochemical, geological and mining-engineering criteria, enabled the determination of a three-degree scale of near-surface gas hazard. Recognition of gas hazard mechanisms in the near-surface zone of post-mining areas is significant for restructuring of the mining industry in Poland and prediction of gas hazard caused by coal mine closure.
-
-
-
Shallow 2D and 3D Seismic Tomography on an Unstable Mountain Slope
Authors H. Horstmeyer, B. Heincke, H. R. Maurer, A. G. Green, H. Willenberg and T. SpillmannAs transport routes and population centres in mountainous areas expand, risks associated with rockfalls grow at an alarming rate. As a consequence, there is an urgent need to delineate mountain slopes susceptible to catastrophic collapse in a safe and non-invasive manner. For this purpose, we have developed a 3-D tomographic seismic refraction technique and applied it to an unstable alpine mountain slope, a significant segment of which is moving at 0.01-0.02 m/year. First-arrivals recorded across the exposed gneissic rock mass have extraordinarily low apparent velocities. Inversion of their traveltimes produces a 3 D tomogram that reveals the presence of a huge volume of very low quality rock with ultra-low to very low P-wave velocities of 500-2700 m/s. Such low values likely result from the ubiquitous presence of dry cracks, fracture zones and faults at a wide variety of scales. They extend to more than 35 m depth over a 200 x 150 m area that encompasses the mobile segment of the slope and a large part of the adjacent stationary rock mass. Although hazards related to the mobile segment have been recognized since the last major rockslides in 1991, those related to the adjacent low quality stationary rock mass have not.
-
-
-
Geophysical Characterization of the V.F. De Xira-Lisbon Fault System, Portugal
Authors J. P. Carvalho, T. Rabeh, F. Carrilho, J. Cabral and M. MirandaThe Lower Tagus Valley (LTV) has suffered large historical seismic events which originated important material damages and loss of lives. Besides the plate boundary activity, the study area has been recently considered an important seismic source to the seismic hazard of the LTV area. The V.F. Xira-Lisbon, was selected as a priority target for investigation, based upon its near-surface expression on the oil-industry seismic reflection profiles, its significance in the Cenozoic basin structural pattern and the apparent relationship to the regional seismicity, its closeness to Lisbon and its seismic potential. Using aeromagnetic, seismic reflection and seismicity along with geological data, new insights into this fault system have been established. Its deep rooting into the paleozoic basement, the unknown northward and southward prolongations and its connection to relocated seismic epicentres are a few examples. The expected total length of the fault will be more than 90km, increasing the estimated magnitude of the maximum credible earthquake and the seismic hazard of Lisbon significantly. Acquisition of high resolution seismic data will help confirming estimated vertical offsets of the fault in Quaternary times, allowing an improved assessment of the seismic potential of the V.F Xira-Lisbon fault system.
-
-
-
The Effect of Vibrations from Wind Turbines on Seismically Sensitive Critical Installations
Authors P. Styles, R. England, I. G. Stimpson, S. M. Toon, D. Bowers and M. HayesIn order to meet Kyoto targets, the UK has set the challenge of reducing carbon dioxide emissions by 60% by 2050. Renewable energy, especially wind power, will be an important contributor with a target of 10% of energy from renewables by 2010. The Southern Uplands of Scotland offer a prime wind resource because of a large region of high topography, appropriate wind conditions and 2 Gigawatt of generating capacity is planned. However, the United Kingdom Comprehensive Test Ban Treaty seismic monitoring site (CBTB) is situated at Eskdalemuir in the Scottish Borders. Concern was expressed that vibration from wind farm developments might prejudice the detection capability of this facility. The Ministry of Defence placed a precautionary blanket objection to wind farm developments within 80 km of Eskdalemuir. In order to assess vibration levels a 10 station broadband seismic network and a 4 station infrasound network were established for 6 months at distances out to 20 km from a 26 turbine wind farm situated on very similar geology and topography to Eskdalemuir and the planned wind farm developments. The study has permitted the identification of the principal propagation mode for ground vibrations from wind turbines and enabled their characterisation.
-
-
-
Progress and Problems in Near Surface Gravity
By S. EloThe paper describes three applications of near-surface gravity: (i) an attempt to estimate in-situ weathering of a dimension stone deposit, (ii) improvements in 3D gravity inversion of overburden thickness and (iii) new results of monitoring the subsidence and density of a landfill. The examples demonstrate the state-of-art in near-surface gravity: mean error of gravity measurements ±0.010 mGal or better, advanced modelling techniques and a demand for highly accurate terrain models.
-
-
-
MRS Study of Groundwater Flow and its Relationship with Sinkholes Development in the Dead Sea Coastal Area
Authors A. Legchenko, M. Ezersky, C. Camerlynck, A. Al-Zoubi and K. ChalikakisA geophysical survey was performed in the Dead Sea costal area of Israel and Jordan. It was carried out in framework of NATO project SfP N° 981128. The goal was trying to understand the processes of sinkholes development caused by the fresh water flow towards the Dead Sea. For that, the Magnetic Resonance Sounding (MRS) method was applied.
Our results reveal a very heterogeneous aquifer with two orders of the transmissivity variation around the investigated area that could be divided into two parts. In the northern part, the aquifer allows intensive circulation of groundwater. It was identified as a karst aquifer thus validating the salt dissolution mechanism of sinkholes development known from the literature. In the southern part, the subsurface is composed of compact clay-type material with low hydraulic conductivity. Development of the karst was not observed.
Basing on MRS results, we suggest that development of the karst in the northern part have changed the local hydraulic gradient and consequently, smaller amount of water is flowing towards the south. Change of the water path may explain why these sinkholes are slowing down their development while in the northern part they continue growing up.
-
-
-
Using ERT and CPTR in Geotechnical Investigations
Authors I. M. Vaara and A. MattssonIn this study the applicability of the electric resistivity tomography and the CPTR-bore logging method was studied in geotechnical soil investigations. Also the induced polarisation effect is discussed. Usually the geotechnical soil investigations utilize lots of drillings and the number of them is set in advance. The aim of this study was to show that by using the ERT-measurements the number of the bore loggings could be diminished and they could also be situated in the most relevant places.
The most important conclusions drawn from the results are that the ERT-method is very useful in geotechnical soil investigations. Also the IP effect gives information on the quality of different soil types. The CPTR gives the point like value of the resistivity of the ground which is important in evaluating the corrosion risk for steel structures. Together with ERT –measurements the CPTR loggings can be very informative about the depth of peat and clay layers.
-
-
-
GPR Investigations in Coastal Sambaqui Archaeological Site in Santa Catarina, South Brazil - Preliminary Results
Authors J. L. Porsani, S. I. Rodrigues, P. C. F. Giannini and P. A. D. DeblasisIn this paper, preliminary results from GPR Investigations are presented, accomplished at Encantada-III coastal sambaqui, in Jaguaruna, Santa Catarina state, South Brazil. This sambaqui consists of sand mound covered by decimetre black sediment layer with carbonatic shells, dated of 4970-4830 years AP (Beta 189713), and could be constructed by societies that inhabited this region during pre-colonial period. GPR profiles show anomalous reflectors, which can be related to targets of archaeological interest. Numeric modelling studies, simulating propagation of electromagnetic wave at coastal sambaquis, presented good accordance with real data obtained in the field. Synthetic model was construct in order to evaluate the performance of GPR method in relation to materials found in that environment, besides helping interpretations of real results. So, the results function as reference to direct excavation activities in burying quest that will be the next step of this searching.
-
-
-
Mapping Ice-Bonded Permafrost with Electrical Methods in Sisimiut, West Greenland
More LessPermafrost delineation and thickness determination is of great importance in engineering related projects in arctic areas.
In this paper, 2D geoelectrical measurements are applied and evaluated for permafrost mapping in an area in West Greenland.
Multi-electrode resistivity profiles (MEP) have been collected and are compared with borehole information.
It is shown that the permafrost thickness in this case is grossly overestimated by a factor of two to three. The difference between the inverted 2D resistivity sections and the borehole information is explained by macro-anisotropy due to the presence of horizontal ice-lenses in the frozen clay deposits.
It is concluded that where the resistivity method perform well for lateral permafrost mapping, great care should be taken in evaluating permafrost thickness based on 2D resistivity profiles alone. Additional information from boreholes or other geophysical techniques is needed for correct interpretation.
-