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Near Surface 2011 - 17th EAGE European Meeting of Environmental and Engineering Geophysics
- Conference date: 12 Sep 2011 - 14 Sep 2011
- Location: Leicester, UK
- ISBN: 978-90-73834-15-6
- Published: 12 September 2011
81 - 100 of 127 results
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Contributions of TDEM Survey in a Seismic Activity Area Triggered by Wells in Paraná Basin, Brazil - Preliminary Results
Authors J. Porsani, E. Almeida, C. Bortolozo and F. SantosThis article present TDEM results on a seismic activity area triggered by groundwater exploitation from deep wells. The study area is situated at Paraná basin, São Paulo state, Brazil. Stations were individually arranged next to wells and along profiles. Preliminary result showed the geoelectrical stratigraphy of Paraná basin. 1st geoelectrical layer is constituted by sedimentary aquifer, followed by top of basalt layer that occur ~60-80 m depth. A fractured zone filled with water within of the basaltic layer was found between 100-300 m depth, which agree to the depth estimated for more than 3000 micro earthtremor hypocenter in the studied region. The bottom of the basalt layer was estimated between ~400-650 m depth. The last geoelectrical layer is characterized by Botucatu sandstone. Results suggest that the high water flow in some wells seems to be related to the presence of fractured zones filled with water founded in the middle of basalt layer. Moreover, there are a good correlation between the seismic activities area and the fractured zones filled with water, which some wells presented the high flux of groundwater. This is a good result which suggest that the shallow seismic activity, can probably is being triggered by water wells drilling.
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Revealing Potential Flow Pathways within the Pow Catchment Using Geophysics - Initial Results and Conceptualisation
Authors L. Mejus, A. Binley and B. SurridgeIn order to help protect groundwater resources we need to understand the pathways of potential contaminants. Whilst the threats from localised sources may be more damaging (locally), the impact of contaminants from diffuse sources is often more difficult to determine because of the spatial extent and complexity of subsurface transport pathways. The first stage in any assessment of threat to groundwater is the establishment of a conceptual model of the groundwater system. Here we present initial results from a study of a sub-catchment of the River Eden in Cumbria, UK. Our focus is on improving the hydrological conceptual model of the catchment, through the use of geophysical measurements.
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Noise Cancellation for Surface NMR - Derivation of Time and Frequency Domain Approaches
Authors M. Mueller-Petke and U. YaramanciEven though surface nuclear magnetic resonance (surface NMR) is the only geophysical technique that provides hydrogeophysical rock properties on the base of direct sensitivity to subsurface water, in many cases surface NMR measurements suffers bad signal-to-noise ratio, and measurements can be carried out only far from sources of electromagnetic noise. To overcome these restriction some approaches using a reference loop based system were developed during the last years (Radic, 2006; Walsh, 2008; Müller-Petke and Yaramanci, 2010; Neyer, 2010). All approaches have demonstrated useful capability to improve S/N. But a comparison that allows for determining properties, i.e., pro and contra of each approach is missing. Thus, to compare time domain with the frequency domain approach, we developed an own frequency domain code beside the existing time domain code. We present a complete derivation of both the time and frequency domain reference technique. Both allow for single and arbitrary number of reference loops. This gives insight into the common idea of both but also the differences in final equations and realization. Finally, this development enables to compare important properties such as applicability at different noise conditions or numerical costs (Müller-Petke and Yaramanci, 2011).
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Two-layer Inversion of Post-calibrated Multi-configuration Electromagnetic Induction Data
Authors A. Mester, E. Zimmermann, J. van der Kruk and H. VereeckenCommon electromagnetic induction (EMI) devices are capable of collecting apparent conductivity values which represent a single value that is assigned to the cumulatively sensed electrical conductivity over a certain depth range. Here, different sensing depths are obtained for different coil orientations, different coil offsets, and different frequencies in the given order of significance. We introduce an inversion scheme that uses post-calibrated EMI data and inverts for a two-layer earth. The inversion minimizes the misfit between the measured and modeled magnetic field by a combined global and local search and does not use any smoothing parameter. Joint inversion of EMI data from horizontal coplanar (HCP) and vertical coplanar (VCP) loop configurations, coil offsets of 1 and 1.22 m, and frequencies of 8 and 15 kHz provides lateral and vertical conductivity variations very similar as observed in an elaborate ERT experiment. Application of this method enables the fast mapping of true conductivity distributions over large areas. This approach can be easily extended for multi-layer inversion when the appropriate multi-configuration EMI data is available.
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1D Joint Inversion of DC and TEM Data for Hydrogeological Applications - Preliminary Results
Authors C.A. Bortolozo, J.L. Porsani, E.R. Almeida and F.A.M. SantosElectrical (DC) and transient electromagnetic (TEM) soundings have been used in great number of hydrological,environmental, and mining exploration studies. The data interpretation usually is done individually by 1D models resulting in ambiguous results. This fact can be explained by how the two different methodologies observe the medium below the surface. The vertical electrical sounding (VES) is good at marking very resistive structures, while the transient electromagnetic sounding (TEM) is very sensitive to map conductive structures. Another difference is that VES is better to detects shallow structures, while TEM soundings can reach deeper layers. In this way, a Matlab program for joint inversion of VES and TEM soundings was developed aiming explore the best of the both methods. Initially, the algorithm was tested with synthetic data and after was used real data from Paraná Sedimentary Basin in Bebedouro region, São Paulo State, Brazil. The geoelectrical model obtained from joint inversion of VES and TEM data are more similar to the real geological condition and ambiguities were minimized. The results with synthetic and real data shows that joint inversion of VES/TEM is better for recovering the simulated models and shows a great potential in geological studies, particularly in hydrogeological studies.
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On the Improvement of Inverse Modeling in Geoelectric Exploration
Authors N.P. Szabo, Á. Gyulai and A.N. ParipásIn the paper, some problems of using conventional inversion methods in geoenvironmental exploration are studied. The series expansion based inversion procedure is presented as a joint inversion method that performs reliable parameter estimation by decreasing efficiently the number of unknowns of the inverse problem. Quality improvement in parameter space is demonstrated by applying the series expansion based 1.5D and 2D CGI (Combined Geoelectric Inversion) inversion methods on DC geoelectrical data. The CGI inversion method was further developed by weighting individual data sets in order to improve inversion results. It is shown that the series expansion based inversion technique is able to resolve near-surface structures such as rapidly varying layer boundaries, laterally inhomogeneous formations and pinch-outs.
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Imaging of a Fault Zone by a Large-scale DC Resistivity Experiment and Seismic Structural Information
Authors T. Gunther, G. Schaumann, P. Musmann and M. GrinatWe present a large-scale resistivity experiment to image a fault system down to a depth of a few hundred meters. A strong transmitter and continuous registration of potential differences is used to acquire time series on a profile of more than 2,km length. The time series' are processed in frequency domain to obtain about 300 apparent resistivities. An independent inversion reveals the course of the fault line but shows a smoothed resistivity distribution. Seismic data from a reflection survey are able to significantly improve the resistivity image by adding structural information to the inverse problem.
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Ambiguity Question in Kinematic Multilayer Refraction Inversion
Authors A.N. Paripas and T. OrmosFor the description of realistic geological models it is important to develop an inversion method that is able to calculate slow lateral changes in the model parameters. But laterally varying parameters of a multilayered structure can cause ambiguity in the inversion process. This is a problem in the use of the kinematic multilayer refraction inversion method developed in the University of Miskolc, because it can interpret laterally changing model parameters (layer thicknesses, and propagation velocities) (for a maximum of 5 geological layers in the same process) described by continuous basis functions expanded in series. The reduction of the arising ambiguity question could be reached by searching for the optimal number of coefficients in the inversion method and it is also important to use different coefficient numbers or different basis functions for the description of the ambiguous parameters. Thus no joint or constrained inversion techniques are needed for the interpretation; our inversion method with simple, quick ray tracing forward modelling is able to handle the ambiguity problem.
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Seismic Horizontal Component Measurement - Reduced Scale Modeling and Benefits in Full Waveform Inversion
Authors R. Valensi, F. Bretaudeau, D. Leparoux, O. Durand, R. Brossier and P. CoteThe study concerns the investigation of the benefits of the horizontal particle displacement component for the seismic velocity parameters imagery using the Full waveform inversion method. A geological consistent model has been firstly numerically modeled. A comparison of the FWI inversion results using either the vertical component measurements or the horizontal component shows that the two components provide complementary information to recover the P wave velocity parameters even if the benefits are less visible for transversal wave velocity. Furthermore, a novel laser interferometric measurement process allowing to measure simultaneously the vertical and horizontal components has been implemented in a reduced physical scale measurement bench previously designed to validate experimentally seismic inversion strategies with a great accuracy: the laser interferometer records the seismic particular displacement, the source is a 100 KHz piezoelectric sensor, the minimum incremental displacement of the sensors is 100 µm with an accuracy of 10 µm. Experimental measurement on the same geological consistent model has been conducted and data are compared to numerical ones. The results show a great accordance between numerical and experimental signals concerning both of the components and suggest that this new measurement method can be applied to a whole experimental campaign at reduced scale.
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Geostatistical Approach for Shale Volume Estimation in Water-bearing Formations
Authors N.P. Szabo and M. DobrokaIn the paper, factor analysis as a geostatistical method used for the interpretation of borehole geophysical data is presented. The result of the procedure is a factor log, which contains valuable information about the lithology of the sequence of strata. We found a strong connection between one special factor and shale content. Analogously to gamma ray index, the so-called factor index was defined, which proved to be a good shale indicator. The method gives consistent results providing reliable information in water-bearing sedimentary structures.
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Pressure Dependence of Seismic Q – A New Petrophysical Model
Authors J. Somogyi Molnar and M. DobrokaThe pressure dependence of quality factor of acoustic waves is an extensively explored rock physical problem. To reasonably evaluate and interpret laboratory measurements, a quantitative model of the mechanism of pressure dependence of quality factor is needed. A new petrophysical model based on simple physical assumptions was developed which describes the relationship between quality factor and pressure as well as acoustic velocity and pressure. The model is based on the idea that microcracks are opened and closed besides different pressure states. The model was applied on quality factor and acoustic velocity data set measured by Prasad and Manghnani or rather Yu et al. The material parameters of the models are determined by using joint inversion method and the laboratory measurements were compared to the theoretical data. The theoretical data matched accurately with measured data proving that the petrophysical model applies well in practice. Studying this phenomenon is relevant because we can infer to the changes in rock pressure by right of seismic/acoustic measurements.
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Microgravity Estimation of Filling up the Near Surface Mineshaft - Example of the Gravity Modelling Usage
By L. SlonkaThe study presents an example of application of the microgravity method in estimation of the degree of filling up old mineshafts, whose existence may be dangerous for the near surface and the infrastructure located on the area. The field data was collected in the area of mining excavations located near the city of Olkusz (Lesser Poland province). The relaxations spreaded in the surrounding of an unfilled object caused emergence of the near-surface deformations, futhermore it causes damages of buildings. An essential part of this study was to discover which objects had been totally filled up and do not create any danger for surrounding infrastructure, and which mineshafts are filled to insufficient extent. One of useful methods of quantitative interpretation of gravity image is gravity modelling. It consist in the calculation of the gravity effect for the customary models and its comparison with measured gravity anomaly, in order to obtain compatibility between field and teoretical curve (with margin of RMS error).
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New Method for Calculation of the Building Effect Correction in Microgravity Technique
Authors J. Panisova and R. PaštekaMicrogravity surveys for archaeological applications conducted in the interior of the buildings require careful data acquisition and processing. We have developed modern, effective and fast data processing procedure for calculation of the building effect correction in microgravity technique. Polyhedral body of historical building is created from images in Eos System’s PhotoModeler Scanner software which is based on close range photogrammetry principles. Comparison of equations for calculation of the gravitational effect of polygonal bodies is presented on a simple test model. The case study from small Slovak church shows that close range photogrammetry offers a possibility to improve microgravity data processing procedures. Our new method provides high accuracy of calculated building effect corrections, thus improving the ability of microgravity technique to detect more difficult identifiable cavities which are situated in a close vicinity to man-made structures.
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Imaging very Shallow Sand Deposits with High Resolution SH Wave Reflection Seismic
Authors A. Almholt, F.W.G. Olsen, R.B. Jørgensen and R. WisenThe main objective for this case study was to map the geological structures along a railway ramp of the great belt tunnel in Denmark. Special focus was put on mapping a thin near surface sandy deposit situated between two clay till units. The purpose for the survey was to provide a detailed geological model as basis for improving the groundwater pumping in the ramp. A SH-wave reflection seismic survey provided a high resolution imaging in the very shallow subsurface and was also the primary source for the geological interpretations. Refraction seismic analysis of the reflection records, surface wave measurements and VSP measurements in two boreholes were also carried out and together with the SH reflection result and available borehole data a detailed geological model was created.
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Comparison of Dominant Frequency and Shear Wave Velocity in Haji Abad City
Authors M. Shahnazi and S. Seyed MohadesFor estimation local response and recognition vulnerable media in urban area, we need to know shear wave velocity and dominant frequency in that area. In some media cannot be preformed seismic refraction operation. But microtremors measurement can be used for acquire dominant frequency. The study preformed in Haji abad city. This city stand on Hormozgan state in Iran. We obtain relevance between two parameters. This result showed that the value of correlation coefficient between shear wave velocity and dominant frequency is about 1. Therefore, shear wave velocity value was obtained from a polynomial function of dominant frequency with high certainty
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Stochastic Analysis of Cross-hole GPR Data for Subsurface Characterization
Authors M. Rossi, A. Binley and G. CassianiGround penetrating radar (GPR) is a well-established geophysical technique, used in particular via specific relationships to estimate hydrological parameters in vadose zone, i.e. moisture content, both from the surface and in boreholes. The principal aim of this work is to have a more complete view of how boreholes GPR ZOP measurements are informative of the subsoil geometry and distribution of relative permittivity. For this purpose an electromagnetic (EM) wave simulator has been applied within a stochastic Monte Carlo framework. In this manner both averaging and critically refracted wave effects are taking into account. Results from synthetic and real ZOP datasets are statistically analysed to deduce what kind of subsoil εr-distributions are resolvable and well defined with a degree of uncertainty. The results illustrate how the often employed direct-wave approach is not able to take into account the complexity of the system. It usually reconstructs a smooth profile, sometimes underestimating the real permittivity: particularly a high εr layer might be underestimated, when it is enclosed between low εr media. Results show that care must be used inverting ZOP data for physical parameter estimation, subsurface stratification could be more complex than appears from direct ZOP evidences.
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Real-time Automated Detection of Buried Utilities for 3D GPR Investigations
Authors P. Mazzucchelli, D. Molteni, E. Cottino and N. di BuonoThe realization of network infrastructures with lower environmental impact and the tendency to use digging technologies less invasive in terms of time and space of road occupation and restoration play a key-role in the development of communication networks: non-destructive investigation and mapping of buried services must match the improvements of new digging equipments. The development of a fully automated 3D GPR processing system allows to avoid processing steps that cannot be carried in-field, highly improving the productivity of optical network deployment by the "low impact mini-trench" technique. The computation and process of the pre-stack reflection angle gathers, built while focusing 3D GPR data, is the core issue of the proposed approach, allowing to detect ducts in real time just while acquiring GPR data, without the need of specific high performance hardware. GPR investigation can be carried on just ahead trenching equipment, as the detection results are immediately available and can be easily understood even by unskilled personnel.
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Practical Results of a Research Project
More LessWe present the practical results we got in the frame of the OTKA project K49604. At first we calculated the consequences of incorrect positioning of the electrodes for various multielectrode systems. In practice these effects were found to be negligible. The only exception is the case of rocky surface, where it is impossible to put the electrodes in the desired positions. From the tensorial geoelectric measurements around a Cistercian Monastery we concluded that areal measurements are able to provide more detailed and unambiguous anomalies than 2D profile measurements. We tested the applicability of 3-D electrical resistivity tomography (ERT) technique to detect landmines in different soil conditions and at various depths. Metallic and non-metallic landmines buried in wet and dry soils had been synthetically modeled. A geoelectrical procedure was elaborated which is able to map multidirectional fissure systems by combining geoelectrical profiling and geoelectrical azimuthal measurements. Results received by using both the so-called null-, and traditional arrays were jointly interpreted. At last we investigated the so-called standardized pricking probe (PP) surveying technique and demonstrated its usefulness in an archaeological study. The optimum PP parameters: horizontal interval, pricking depth, observable quantity and its way of presentation were optimized through field experiments.
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Application of the Controlled-source RMT Method for the Solution of Engineering Tasks in Chukotka Region
Authors A.E. Simakov and A.K. SaraevEquipment of controlled source radiomagnetotelluric method (CSRMT) operates in frequency band 1-1000 kHz and experience of its application for the solution of engineering tasks in Chukotka region (far North-East of Russia) are described. The CSRMT method allows us to work in remote areas where there are not enough radio transmitters. A new RMT-C system includes transmitter and receiver groups with a grounded electric dipole as a controlled source. Using of 3-4 main controlled source frequencies from the range 1-150 kHz and their several odd harmonics allows us to realize CSRMT soundings in frequency band 1-1000 kHz. Application of such technique does not require the emitting of a big number of frequencies and a measurement at one station takes little time. Results of investigations by the RMT-C system in Chukotka region has been confirmed by drilling.
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Geophysical Investigation of Track Defects
More LessThe article presents possibilities of application of selected geophysical methods in railway engineering. The text below is supported mainly by the measurements performed under the INNOTRACK projects (6th FP EU) at the sites in the Czech Republic, France, Spain and Sweden. The geophysical testing has proved that the geophysical methods can reliably, quickly, in detail and a relatively low cost inform about problematic zones on the track. The effect of the geophysical application can be enhanced by long-term monitoring track segments. Virtually at all sites subjected to the measurements, the methods of refraction seismics, seismic tomography, resistivity tomography and gravimetry were applied.
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