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Near Surface 2008 - 14th EAGE European Meeting of Environmental and Engineering Geophysics
- Conference date: 15 Sep 2008 - 17 Sep 2008
- Location: Kraków, Poland
- ISBN: 978-90-73781-56-6
- Published: 17 September 2008
121 - 130 of 130 results
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In-mine Geoelectric Methods for Detection of Tectonic Disturbances of Coal Seams
Authors T. Ormos, Á. Gyulai and M. DobrókaIn-mine geoelectric methods – the geoelectric seam-sounding and geoelectric transillumination – were applied for detection of fault zones in a coal mine. The measured data were interpreted using geoelectric tomography algorithm. Appreciable agreements were found between the location of tectonic zones predicted by the interpretation and those observed during the mining extraction.
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Modelling Overburden Thickness for Applications in Mining Technologies
More LessMany drift prospecting methodologies using geophysical and geochemical surveys are dependant on overburden thickness to successfully locate mineral deposits. Efficiency of these methods relies on the overburden’s ability to reflect underlying bedrock. Till sampling for geochemistry or indicator minerals in thick overburden may yield data difficult to interpret. A basic knowledge of sediment thickness and glacial sediment genesis and ice-flow history is required. Most models of overburden thickness are developed from subsurface geological data with abundant “depth-to-bedrock” information, in the form of water well logs, drill holes or seismic shot holes. Overburden thickness models can also be developed where there is limited or no primary “depth-to-bedrock” information, or where the primary information, such as drill holes, is clustered. In these cases, a surficial geology map can provide an important source of overburden thickness data. The best approximate overburden thicknesses are derived from surface morphology of the surficial units, obtained from both air photo/satellite interpretation and traditional mapping activities.
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Evaluation of a High-frequency Seismic Source System in Mining Application
More LessIn the year 2007 two seismic measuring campaigns were carried out in the research and teaching mine `Reiche Zeche' in Freiberg (Saxonia, Germany). 24 three-component geophones, developed by the GeoForschungsZentrum Potsdam (Germany), were deployed in small boreholes along two galleries, with geophone intervals of around 7.5 m. The maximum distance between source system and geophones was around 40 m. The seismic source system consists of two actuators, based on the magnetostrictive effect. The actuators are custom-made by ETREMA Products, Inc. (USA). For the two actuators an adaptive, real-time, closed loop control was used with a sweep signal of a bandwith ranging from 300 Hz up to 6 kHz. The Shover principle was applied for shear wave generation. During campaign 1 the source system was principally tested. The focus of campaign 2 was to test signal repeatability and compare different recording systems to optimize the source system. The Shover principle could not be successfully applied until yet.
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Surface Seismic Investigations for the Determination of Water Flow Directions in Underground Melting of Sulphur Deposit
Authors R.P. Slusarczyk and J. DecThis paper shows the results of seismic research on some problems of sulphur in situ mining. Before the field measurements we constructed seismogeological model and calculated the synthetic seismograms. It is observed a good correlation between the state of the exploited deposit and quality of reflections on seismic records. The use of seismic method to determine the range of subsidence provoked by well mining of sulphur is presented. Comparison of the seismic sections before and during exploitation creates the possibility to determine the process of changing structure of the deposit and overburden strata and using this information for technological purposes. The water saturated zones are observed on seismic record as a zone without reflections and with decay of seismic energy. The information from few seismic profiles allows to construct the seismic map with situation of water saturated zones between damaged well and place with technological water on surface. Two examples of the seismic investigation conducted on the well mining of sulphur area are presented. Both are connected with the danger to main road on the surface caused by technological water uncontrolled flow.
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Seismicity Associated with a Coal Extraction in the Low Strength Rocks Formations, Based on Coal Mine "Ziemowit
Authors T. Gebis, A. Golda and G. SladowskiHigh seismic activity on Coal Mine “Ziemowit”, occurred at the beginning of the eighties, was a big surprise for a mining science. Mining seismicity has been connected with exploitation of coal seams 207, 208 and 209 – laziskie series. Theory, that low strength rock formations cannot generate high energetic tremors (1E5 - 1E7 J and more) has been verified by the reality. Since that time a Geophysics Station on Coal Mine “Ziemowit” has recorded more than 1300 such tremors. In this paper presented level of seismic activity and rockburst danger in Coal Mine “Ziemowit”. It has been shown changes in the way of calculating rockburst danger and paid attention for the necessity of further studies of mine tremors phenomena.
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Analysis of the Rupture Propagation Velocity for Seismic Events at Rudna Copper Mine, Poland
Authors B.M. Domański and A. KotwickiDetermination of source time functions based on the empirical Green’s function technique provides the rupture velocity and other source parameters for unilaterally propagating ruptures. Spatial distribution of source time function durations and amplitudes permits to calculate these parameters.
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Data Resolution Matrix and Model Resolution Matrix of Rayleigh-wave Inversion Using a Damped Least-square Method
Authors J. Xia, R.D. Miller and Y. XuEstimation of shear (S)-wave velocities by inversion of high frequency ( 2 Hz) Rayleigh waves has been given increasingly more attention by the near-surface geophysical community with application to a variety of near-surface geological and geophysical problems. For a given near-surface geophysical problem, it is essential to understand how well the data, calculated according to a layered-earth model, might match the observed data. It is also important to recognize that a match may only be possible for data within a certain frequency range or at specific frequencies because the sensitivity of Rayleigh-wave phase velocities due to changes in S-wave velocities varies with frequency. To provide insights into the process of inverting Rayleigh-wave phase velocities to estimate S-wave velocity structure, we introduced and discussed a data resolution matrix and a model resolution matrix of a damped least-square method. The resulting discussion indicated that each near-surface geophysical target can only be resolved using Rayleigh-wave phase velocities within specific frequency ranges and higher mode data are normally more accurately predicted than fundamental mode data because of restrictions on the data kernel of the inversion system. We proposed an inversion of data selected according to the data resolution matrix. The synthetic and real-world examples demonstrated that the proposed inversion could produce models with higher data resolution as well as higher model resolution.
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Estimation of Bedrock Depth Using the Horizontal-to-vertical (H/V) Ambient-noise Seismic Method
Authors J.W. Lane, E.A. White, G.V. Steele, J.C. Cannia and J.H. WilliamsEstimation of shear (S)-wave velocities by inversion of high frequency ( 2 Hz) Rayleigh waves has been given increasingly more attention by the near-surface geophysical community with application to a variety of near-surface geological and geophysical problems. For a given near-surface geophysical problem, it is essential to understand how well the data, calculated according to a layered-earth model, might match the observed data. It is also important to recognize that a match may only be possible for data within a certain frequency range or at specific frequencies because the sensitivity of Rayleigh-wave phase velocities due to changes in S-wave velocities varies with frequency. To provide insights into the process of inverting Rayleigh-wave phase velocities to estimate S-wave velocity structure, we introduced and discussed a data resolution matrix and a model resolution matrix of a damped least-square method. The resulting discussion indicated that each near-surface geophysical target can only be resolved using Rayleigh-wave phase velocities within specific frequency ranges and higher mode data are normally more accurately predicted than fundamental mode data because of restrictions on the data kernel of the inversion system. We proposed an inversion of data selected according to the data resolution matrix. The synthetic and real-world examples demonstrated that the proposed inversion could produce models with higher data resolution as well as higher model resolution.
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Repeatability of Towed Magnetic Data for Archaeological Prospection within a Sand and Gravel Mineral Deposit
Authors J.S. Upwood, C. Leech, I.A. Hill and N. LinfordThe Geophysical Exploration Equipment Platform (GEEP) was used to survey an area of known archaeological interest in Shelford, Nottinghamshire. The site consisted of varying depths of sand and gravel deposits reaching a maximum thickness just under 10 meters, although the archaeological remains are likely to be much closer to the surface. An array of six caesium magnetometer sensors were set up at 0.6m separations on the GEEP and towed across the site. A section of the site was surveyed again the following day to determine the repeatability of the towing method used. Sand and gravel deposits in the region produced a level of background magnetic variation across the traverses and archaeological features were clearly observed outside this trend. A differential GPS system was mounted on the GEEP to provide positional data ensuring a reliable comparison between datasets was achieved. Data obtained on the repeat survey shows extreme likeness to that observed on the original dataset indicating the repeatability of the GEEP towing method for small separation magnetic surveys in sand and gravel environments. It took the GEEP operator three and a half hours to collect the original 6 hectare dataset, and an additional forty minutes to complete the repeated section.
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Modeling the EMI Decay Response of Medium and Large UXO with Conventional and B-field Sensors
Authors M.W. Asten and A.C. DuncanWe compare the response of a conventional dB/dt EMI system (Geonics EM63) with a new system which utilizes a 3-component fluxgate B-field sensor. The B-field system has the advantage of providing decay curve information to times a factor of 5 to 10 greater than is achieved by the conventional dB/dt system. The transition from intermediate to late-time decay behavior is predicted theoretically to occur about a factor of two earlier in time for the B-field system, and this is confirmed by plotted observed data. Longer pulse times, lower transmitter frequencies, and longer decay curves are possible with the B-field system due to its wider bandwidth and lower noise at the low-frequency end of the spectrum. The decay constant for the medium and large munitions items considered here ranges from 12 to 25 msec and all decays when excited and measured with the EM63 EMI metal detector are incorrectly estimated as too small, due to the limited pulse-length and off-time intervals in the EM63 system. We propose that the improved ability of the B-field system to estimate the fundamental decay constant of a conductive permeable object will assist in UXO target discrimination, especially for situations where decay curves at earlier sample times are perturbed by ancillary scrap, or the response of magnetic earth.
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