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Seismic velocities in complex media
361A tool for remote monitoring of rock slopes. A back analysis method to monitor slope stability is presented. Using mechanical properties calculated from the back analysis and GPSdetermined displacements, factors of safety can be evaluated. Application to a large cut slope in weathered sandstone is illustrated.
Geophysical techniques See also: 936039, 936138 936225 Microgravity method for detection of abandoned mines in New Jersey Chatge, S L Bull Assoc Engng Geol V30, N1, March 1993, P79-85 Abandoned mines are a potential hazard in urban areas of New Jersey. Two shallow disused workings have been located using the microgravity method. Synthetic models were used to simulate the expected gravity anomalies. At the first site, an iron ore mine, two profile lines were laid at right angles to the strike of the magnetite deposit in the amphibolite host rock. Mine workings about 3m square by 1.5m deep and filled with soil were indicated. Four parallel profile lines were used to detect an empty vertical shaft at depth about 20m at an old copper mine. Subsurface investigations confirmed the microgravity survey predictions.
936226 Characterization of sediments by high-frequency echo-sounding Forsgren, G; Malmgren, L; Brydsten, L; Jansson, M Environ Geol V21, N1/2, April 1993, P14-18 Sediments of the shallow Ore estuary in the Gulf of Bothnia have been characterised using a 200kHz echo sounder. Fine and coarse grained sediments were distinguished according to their acoustic signal patterns using 4 main criteria: roughness of the line surface, line thickness, occurrence of white noise, and double echo. Echogram-derived characteristics were calibrated against laboratory measured physical properties. The echo-sounding technique proved reliable and simple for determining the spatial distribution of different kinds of sediments in shallow water.
936227 Use of electromagnetic measurements of apparent soil electrical conductivity to predict boulder clay depth Brus, D J; Knotters, M; van Dooremolen, W A; van Kernebeek, P; van Seeters, R J M Geoderma V55, N1/2, Oct 1992, P79-93 Bulk soil electrical conductivity can be measured quickly and accurately using electromagnetic induction devices. At a site of boulder clay overlain by sand, soil conductivity was measured under both wet and dry conditions using two different instruments. Exponential and spherical models have been applied to fit the relation between depth to boulder clay and conductivity. Comparisons are made between results of the different instruments and fitting models.
936228 Estimation of elastic parameters from AVO effects in the Tan-P domain Helgesen, J; Landro, M Geophys Prospect V41, N3, April 1993, P341-366 A quantitative AVO algorithm capable of identification of lithology, pore fluid, and petrophysical parameters from seismic data is presented. It uses band limited PP reflection coefficients in the Tau-P domain to estimate P and S wave
velocities, density, and layer thickness. Preprocessing with the Radon transform and multiple attenuation is necessary to obtain these reflection coefficients. Various inversion tests using synthetic data with white Gaussian noise and modelling errors have been performed. Source directivity is seen to be an important parameter in processing. The main features of the reference model were reproduced.
936229 Quantitative determination of uncertainties in seismic refraction prospecting Liu, C; Stock, J M Geophysics V58, N4, April 1993, P553-563 A model of propagation of refracted seismic waves in planar layered structures is presented, in which quantification of errors from various sources is possible. The mixed variance component model separates errors originating on the surface from those resulting from inhomogeneity of subsurface layers. In addition, the velocity-depth curve with its confidence limits can be obtained at any relevant point along the line. Data from a crustal scale seismic refraction line are analysed and the unsuitability of the linear regression model for first arrivals for this data set is demonstrated. Refinements to the approach are discussed. The model can also be applied to smaller scale refraction problems.
936230 Geoclectrical methods applied to structures of arbitrary shapes Alfano, L J Appi Geophys II29, N3/4, April 1993, P193-209 When geoelectrical prospecting in areas of complex geology, large numbers of data are collected for the target area and rigorous inversion methods requiring powerful computers are necessary for processing. The surface charge algorithm for computation of apparent resistivity values from a structural model is presented. Such ideal methods arc complicated and expensive and it may be necessary to resort to traditional procedures such as vertical sounding. The pole-dipole array is suggested as the most suitable in this case. Field examples of continuous pole-dipole soundings are shown.
936231 Two-dimensional resistivity imaging and modelling in areas of complex geology Griffith, D H; Barker, R D J Appl Geophys V29, N3/4, April 1993, P211-226 A linear array of up to 32 electrodes connected to a computercontrolled switching module and a resistivity meter is illustrated for automatic data collection for electrical tomography surveys. A brief description is given of the processing to produce 2D true resistivity images of the subsurface. Limitations and capabilities are discussed. Images from synthetic and field data are presented and comparisons made between interpretations using automated image processing and a manual iterative approach.
936232 Seismic velocities in complex media Grau, G J Appi Geophys V29, N3/4, April 1993, P271-284 The use of velocity models for reflection seismic survey and difficulties in extracting pertinent parameters from the data in conditions of complex geology are discussed. Regions with complex geology are defined and the nature of data from such regions illustrated. Velocity estimation in complex regions, migration consistency, and traveltime tomography are described. With care, it is possible to obtain accurate subsurface images and indications of lithology.
© 1993 Pergamon Press Ltd. Reproduction not permitted
Geophysical techniques See also: 936039, 936138 936225 Microgravity method for detection of abandoned mines in New Jersey Chatge, S L Bull Assoc Engng Geol V30, N1, March 1993, P79-85 Abandoned mines are a potential hazard in urban areas of New Jersey. Two shallow disused workings have been located using the microgravity method. Synthetic models were used to simulate the expected gravity anomalies. At the first site, an iron ore mine, two profile lines were laid at right angles to the strike of the magnetite deposit in the amphibolite host rock. Mine workings about 3m square by 1.5m deep and filled with soil were indicated. Four parallel profile lines were used to detect an empty vertical shaft at depth about 20m at an old copper mine. Subsurface investigations confirmed the microgravity survey predictions.
936226 Characterization of sediments by high-frequency echo-sounding Forsgren, G; Malmgren, L; Brydsten, L; Jansson, M Environ Geol V21, N1/2, April 1993, P14-18 Sediments of the shallow Ore estuary in the Gulf of Bothnia have been characterised using a 200kHz echo sounder. Fine and coarse grained sediments were distinguished according to their acoustic signal patterns using 4 main criteria: roughness of the line surface, line thickness, occurrence of white noise, and double echo. Echogram-derived characteristics were calibrated against laboratory measured physical properties. The echo-sounding technique proved reliable and simple for determining the spatial distribution of different kinds of sediments in shallow water.
936227 Use of electromagnetic measurements of apparent soil electrical conductivity to predict boulder clay depth Brus, D J; Knotters, M; van Dooremolen, W A; van Kernebeek, P; van Seeters, R J M Geoderma V55, N1/2, Oct 1992, P79-93 Bulk soil electrical conductivity can be measured quickly and accurately using electromagnetic induction devices. At a site of boulder clay overlain by sand, soil conductivity was measured under both wet and dry conditions using two different instruments. Exponential and spherical models have been applied to fit the relation between depth to boulder clay and conductivity. Comparisons are made between results of the different instruments and fitting models.
936228 Estimation of elastic parameters from AVO effects in the Tan-P domain Helgesen, J; Landro, M Geophys Prospect V41, N3, April 1993, P341-366 A quantitative AVO algorithm capable of identification of lithology, pore fluid, and petrophysical parameters from seismic data is presented. It uses band limited PP reflection coefficients in the Tau-P domain to estimate P and S wave
velocities, density, and layer thickness. Preprocessing with the Radon transform and multiple attenuation is necessary to obtain these reflection coefficients. Various inversion tests using synthetic data with white Gaussian noise and modelling errors have been performed. Source directivity is seen to be an important parameter in processing. The main features of the reference model were reproduced.
936229 Quantitative determination of uncertainties in seismic refraction prospecting Liu, C; Stock, J M Geophysics V58, N4, April 1993, P553-563 A model of propagation of refracted seismic waves in planar layered structures is presented, in which quantification of errors from various sources is possible. The mixed variance component model separates errors originating on the surface from those resulting from inhomogeneity of subsurface layers. In addition, the velocity-depth curve with its confidence limits can be obtained at any relevant point along the line. Data from a crustal scale seismic refraction line are analysed and the unsuitability of the linear regression model for first arrivals for this data set is demonstrated. Refinements to the approach are discussed. The model can also be applied to smaller scale refraction problems.
936230 Geoclectrical methods applied to structures of arbitrary shapes Alfano, L J Appi Geophys II29, N3/4, April 1993, P193-209 When geoelectrical prospecting in areas of complex geology, large numbers of data are collected for the target area and rigorous inversion methods requiring powerful computers are necessary for processing. The surface charge algorithm for computation of apparent resistivity values from a structural model is presented. Such ideal methods arc complicated and expensive and it may be necessary to resort to traditional procedures such as vertical sounding. The pole-dipole array is suggested as the most suitable in this case. Field examples of continuous pole-dipole soundings are shown.
936231 Two-dimensional resistivity imaging and modelling in areas of complex geology Griffith, D H; Barker, R D J Appl Geophys V29, N3/4, April 1993, P211-226 A linear array of up to 32 electrodes connected to a computercontrolled switching module and a resistivity meter is illustrated for automatic data collection for electrical tomography surveys. A brief description is given of the processing to produce 2D true resistivity images of the subsurface. Limitations and capabilities are discussed. Images from synthetic and field data are presented and comparisons made between interpretations using automated image processing and a manual iterative approach.
936232 Seismic velocities in complex media Grau, G J Appi Geophys V29, N3/4, April 1993, P271-284 The use of velocity models for reflection seismic survey and difficulties in extracting pertinent parameters from the data in conditions of complex geology are discussed. Regions with complex geology are defined and the nature of data from such regions illustrated. Velocity estimation in complex regions, migration consistency, and traveltime tomography are described. With care, it is possible to obtain accurate subsurface images and indications of lithology.
© 1993 Pergamon Press Ltd. Reproduction not permitted