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Near Surface Geoscience 2016 - 22nd European Meeting of Environmental and Engineering Geophysics
- Conference date: September 4-8, 2016
- Location: Barcelona, Spain
- Published: 04 September 2016
181 - 189 of 189 results
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A New Procedure of Reduction to Pole of Magnetic Data - Improved Noise Rejection Capability
Authors H. Szegedi, A. Kiss, M. Dobróka and J. Somogyi MolnárIn geophysical research it is an important objective to find more accurate measuring and more effective data processing methods. Measurement data always contain noise, which can mislead the interpreter, or hide useful information. The often used traditional DFT algorithm shows low noise rejection capability. On the other hand there are robust methods to solve the overdetermined inverse problem with excellent noise rejection capabilities. Therefore we suggest a new inversion based Fourier transformation method, where the continuous frequency spectrum is discretized with series expansion and the series expansion coefficients as model parameters are determined in the framework of the Iteratively Reweighted Least Squares (IRLS) algorithm using the so-called Cauchy-Steiner weights. In this paper the method was tested on noisy synthetic magnetic data generated above two magnetic bodies. The results prove the successful applicability of our inversion based S-IRLS-FT algorithm.
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Coal Mine Cavity Detection Using Electrical Resistivity Tomography - A Joint Inversion of Multi Array Data
Authors A.K. Bharti, S.K. Pal, S.K. Ranjan, R. Kumar, P. Priyam and V.K. PathakThe term subsurface cavity is used to refer to all subsurface features that are termed as goaf, caves, caverns, tunnels, mines, abandon gallery. Subsurface cavity can be water filled or air-filled rock debries. Subsurface cavities may occur naturally or due to manmade activity. Therefore, it is necessary to determine their location and size in order to evaluate the risk of subsidence and to draw up plans for restoration and safety. Electrical Resistivity Tomography (ERT) is an advanced geophysical method used to map the subsurface resistivity distribution by making simultaneous potential measurements across the multielectrodes inserted in the ground surface. It has three main units’ viz., transmitter, receiver and microprocessor. The resistance of layered earth is automatically calculated using inbuilt microprocessor which display and write in digital form. In the this study, 2D ERT sections have been generated along a profile over Sidpoki colliery, Jharia coalfield, India using Wenner, Schlumberger, Dipole-Dipole, Gradient arrays and joint inversion inversion of all array data collected by a state-of-the-art 61-channel 64 electrode FlashRES-Universal electrical resistivity tomography (ERT) data acquisition system. The present study reveals that different resistive anomalous features delineated using joint inversion gives best suitable results for delineation of relatively high resistivity voids.
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Application of Data Weighting Technique to 3D Inversion of Complex Resistivity Data
More LessComplex resistivity method is a frequency domain IP method, and it was very effective means for the mineral exploration. With the rapid development of measurement instruments, it extend its application field to the environmental problems recently. Many kind of inversion technique were applied to the existing 2/3D inversion algorithms to achieve more precise interpretation. As one of this trial, data weighting technique was tried to existing 3D inversion algorithm. Zeta system manufactured by the Zonge Co. was used to get complex resistivity data, and it gave additional information of acquired data with basic amplitude and phase. These information was neglected in our previous inversion algorithm. In this paper, data weighting technique was developed to use it and reprocessed to the existing data set that was used to evaluate the ground reinforcement effect. Through the newly applied data weighting, the shape of phase anomaly was changed in the deeper part of inversion block since data weighting affect the change of these area in accordance with the data quality. This data weighting technique could be effective tools to get more reliable inversion results from 3D complex resistivity survey.
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Reduction of 3D Borehole Effects in the Inversion of 2.5D crosshole ERT Data
More LessIt is well known that borehole fluid effects in crosshole electrical resistivity tomography (ERT) can produce serious image artifacts using conventional inversion algorithms that do not account for borehole effects. Using the analytical solution for an infinitely long borehole model in a half-space, we demonstrated that the borehole effects depend on the borehole radius and on the resistivity contrast between the borehole fluid and the surrounding rock formation. To overcome the borehole effects in the crosshole ERT surveys, we developed a new 2.5D inversion algorithm incorporating the boreholes. The new inversion algorithm yielded an electrical resistivity image that was devoid of artifacts around the boreholes.
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Integrated Workflow for Surface-wave Dispersion Inversion and Profiling
Authors S. Pasquet and L. BodetWhile surface-wave prospecting methods are classically applied for the one-dimensional (1D) estimation of shear (S-) wave velocities (Vs), two-dimensional (2D) profiling still requires implementing specific processing and inversion tools that are not yet widely available in the community. We present here a free and open-source tool performing surface-wave inversion and profiling (SWIP) in order to retrieve 2D lateral variations of Vs from typical seismic shot records. Windowing and stacking techniques are implemented to compute dispersion images with smooth lateral variations and enhanced signal-to-noise ratio. Dispersion curves are extracted for each window with an error in phase velocity taking into account the higher uncertainties at low frequency. These curves are then inverted for each window position using a Monte Carlo approach and a refraction tomography-based parameterization. Models matching the observed data within the error bars are selected to build a misfit-weighted final model and estimate the investigation depth. Finally, 1D models obtained for each window position are merged into a 2D Vs section.
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Separation of a Single Mode of Rayleigh Waves Using Quaternion SVD in Vertically-heterogeneous Media
By A. SajevaI propose a wave-separation method that separates a single Rayleigh-wave mode from body waves and from other modes, using quaternions to represent the multi-component seismic data recorded by an array of vector-sensors. This method decomposes the signal into narrow-frequency bands, which are subjected to both a velocity correction and a polarisation correction. The aim of these corrections is to reduce the mode of interest to a quasi-monochromatic wave packet with infinite apparent velocity and quasi-circular polarisation. Once written in quaternion notation, I refer to this wave packet as “quaternion brick”. It can be proved that this quaternion brick maps into the first quaternion eigenimage of the quaternion SVD (QSVD). I apply this method to vertically-heterogeneous elastic models. The method seems to correctly extract the selected Rayleigh-wave mode and to separate it from body waves. The separation between different modes is more challenging. It results that, when two modes interfere in the near-offset portion, a more accurate separation can be obtained by characterising the mode of interest in the far-offset portion and then extrapolating it in the near-offset portion (where the two modes overlap) using the properties of the right singular vector of the QSVD.
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Surface-related Multiple Elimination Using Seismic Interferometry for Land Seismic Data
More LessLand seismic data are often irregularly sampled in space and are contaminated with various noises such as coherent noise and random noise. Thus, data preprocessing, such as noise attenuation, interpolation, static correction, etc., should be applied to land data. In this study, we propose applying seismic interferometry instead of applying preprocessing procedures such as data interpolation and elevation correction, for surface-related multiple elimination. With seismic interferometry, we can also improve signal-to-noise ratio at the same time. Several synthetic tests for acoustic and elastic (specifically vertical components of displacements) cases show that our method can be used to perform surface-related multiple elimination and to reconstruct data with higher signal-to-noise ratio without multi-step data preprocessing procedures. However, preprocessing procedures to remove surface waves and direct waves should still be applied.
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Neves-Corvo 3D - A High-resolution Seismic Survey at a Mine Camp Scale
Authors S. Ziramov, J. Kinkela and M. UrosevicFour consecutive 3D seismic surveys were acquired across the Neves Corvo mining camp in Portugal over a period of two years. The first survey undertaken was in 2011 over the known Semblana deposit, which proved that the 3D seismic method was capable of producing a very clear image of a complex underground orebody at this site. The main objective of the subsequent seismic surveys was the definition of the main structures, which were controlling mineralisation. Initial processing of the seismic data showed great promise in resolving the complex structural environment and also hinted at the possibility for direct targeting from seismic data. However, the quality across four different surveys was highly variable due to different acquisition geometry and source parameters. Moreover, initial processing did not involve preserved relative amplitude processing, which was key for the direct targeting of ore shoots. After successful application of surface consistent amplitude compensation, it turned out that pre-conditioning in the offset planes, followed by exclusion of unsuccessfully imaged events prior to stacking, produced the highest quality fully merged PSTM seismic cube. This cube could then be used for direct targeting with much more certainty than with any other processing result produced before.
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Laboratory and Field Measurements of Electrical Resistivity to Study Heap Leaching Pad No. 3 at Sarcheshmeh Copper Mine
Authors M. Moradipour, H. Ranjbar, A. Hojat, S. Karimi Nasab and S. DaneshpajouhSummaryIn this paper, we present the results of laboratory and field measurements of electrical resistivity used over a part of heap no. 3 at Sarcheshmeh copper mine, Iran. Heap leaching technology has been used at Sarcheshmeh mine to extract low-grade copper ores with dilute sulphuric acid. Although careful attention is given to have a regular acid sprinkling on the surface of the heap, permeability changes of the pads produce an irregular pattern of leachate distribution under the surface. It is very important to monitor the leachate movement within these structures. Geophysical methods can provide invaluable insight into heap leach pads and detect possible areas of copper being remained. Before performing resistivity field surveys, laboratory measurements were performed on the samples taken from Sarcheshmeh low grade ores and saturated in sulfuric acid. Then, a small part of heap no. 3 was selected for resistivity field surveys. Two-dimensional resistivity surveys were carried out along three parallel survey lines with the Wenner-Schlumberger array. The results of resistivity measurements showed that the resistivity values were in the range of 3–13Ωm. With the help of the results obtained from laboratory measurements, the acid saturated zones, low moisture and dry zones within the heap were detected.
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