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Qβ estimates from spectral ratios and multiple lapse time window analysis: results from an underground research laboratory in granite
18A
SITE INVESTIGATIONS:GEOPHYSICS
951126 Towards an improved seismic imaging technique for crustal structures: the Lithoprobe Sudbury experiment B. Milkereit, D. J. White & A. G. Green, Geophysical Research Letters, 21(10), 1994, pp 927-930. Under the Canadian Lithoprobe program, conventional low(10-55 Hz) and high-frequency (30-140 Hz) vibroseis reflection surveys were conducted across the Sudbury Structure. The main objective of the study was to evaluate the performance of seismic exploration techniques in a complex, mainly crystalline geological setting. The Sudbury experiment demonstrated that high input frequencies can be preserved through appropriate acquisition and processing procedures. Consequently, the high-frequency seismic data proved capable of imaging complex shallow crustal structures not 'seen' by the conventional low-frequency seismic survey. (from Authors) 951127 Seismic reflectivity of the Sudbury Structure North Range from borehole logs D. J. White & 7 others, Geophysical Research Letters, 21(10), 1994, pp 935-938. Results from borehole geophysical logs, full waveform sonic logs, VSP and laboratory core sample measurements indicate that lithologic variations within the Sudbury Igneous Complex (SIC) and footwall rocks are the primary cause of reflections observed regionally on the multi-channel seismic reflection profiles. The effects of macroscopic fracturing and low-grade alteration on the seismic response are only important to a depth of ,,~320 m. The major lithologic units of the SIC and footwall rocks in the North Range of the Sudbury structure have contrasting physical properties. The contrasting velocities and densities of these units imply that the granophyre/quartz-gabbro contact and the SIC/footwall transition can be mapped regionally using seismic reflection methods. (from Authors)
951128 Three component vertical seismic profiling (VSP) experiment in the Sudbury Basin X. Miao, W. M. Moon, B. Milkereit & C. J. Mwenifumbo, Geophysical Research Letters, 21(10), 1994, pp 939-942. A three component VSP experiment was carried out in the metasedimentary Whitewater group of the Sudbury Structure. Processing of the VSP data focused on velocity analysis, wavefield separation, shear-wave analysis, waveform modelling, hodogram analysis, and integration of surface-seismic and borehole geophysical data. Wavefield separation processing and synthetic VSP modelling resulted in a realistic velocity model and the corridor-stacked compressional section correlates well with the surface seismic reflection data. Besides establishing a direct link between borehole lithologies and surface seismic images, the VSP data, using three component particle motion velocity hodograms, provide an independent estimate of true reflector dip in the subsurface of the Sudbury Structure. (from Authors)
951129 Implications of laboratory electrical measurements on interpretation of EM-surveys and origin of the Sudbury Structure T. J. Katsube & M. Salisbury, Geophysical Research Letters, 21(10), 1994, pp 947-950. Electrical resistivity and effective porosity have been measured for 52 drillcore samples representing major sedimentary and igneous lithologies exposed in the Sudbury Structure (SS). While zones of low resistivity are known to exist in the upper sedimentary formations, rocks at depth arc generally
characterized by high resistivities (104-7 × 104 l'l-m), leaving the source of the deep EM anomaly unexplained. However, samples with low resistivities (7-20 [l-m) have been unexpectedly found in the cores from lower sections of the SS, depths possibly corresponding to that of the EM anomaly. These samples are characterized by low porosities (0.3-0.6%), normal bulk densities (2.78-2.81), and a porphyritic texture with a blackish matrix, suggesting carbon as the likely cause of the low resistivities. (from Authors)
951130 Q~ estimates from spectral ratios and multiple lapse time window analysis: results from an underground research laboratory in granite A. J. Feustel & R. P. Young, Geophysical Research Letters, 21(14), 1994, pp 1503-1506. An experiment to measure quality factor (Q) in-situ was carried out at the Underground Research Laboratory in Manitoba, Canada using the Spectral Ratio technique and a form of the Multiple Lapse Time Window Analysis technique. Results from the Spectral Ratio experiment gave Swave quality factor (QI~) of 114 _+ 18. Based upon the short duration of the first arrival pulses and low scattered wave energy in the signal coda, it is concluded that the Spectral Ratio technique measured the intrinsic attenuation of the rock mass. Further analysis using the more recently developed Multiple Lapse Time Window Analysis gave results for intrinsic QI3 (Q~) of between 85 and 100. Conversely, values for scattering Q~ (Qs) were greater than 800. (from Authors)
951131 The fields from a finite electrical dipole - a new computational approach K. I. Sorensen & N. B. Christensen, Geophysics, 59(6), 1994, pp 864-880. Except for small magnetic dipole sources, all electric and magnetic sources are composed of lengths of straight wire, which may be grounded. If the source-receiver separation is large enough, the composite electrical dipoles may be considered to be infinitely small, and in a 1-D earth model the fields are expressed as Hankel transforms of an input function, which depends only on the model parameters. The theory of fast Hankel transforms is extended to include integrals of Hankel transforms, and a method is devised for calculating the filter coefficients. Unlike the fast Hankel transform, the computation involved in the integrated Hankel transforms is not a true convolution, and so a set of filter coefficients must be calculated for each source-receiver configuration. (from Authors)
951132 Electric study of fracture anisotropy at Falkenberg, Germany S. A. AI Hagrey, Geophysics, 59(6), 1994, pp 881-888. Electric and electromagnetic methods have been applied for mapping subsurface fractures and the directional dependence of in-situ electric parameters at the hot dry rock site at Falkenberg, Germany. This study includes the determination of several anisotropy parameters like the mean, longitudinal and transverse resistivity components, the anisotropy coeffident and the strike angle. (from Author)
951133 On the influence of 3-D structures in the interpretation of transient electromagnetic sounding data M. Goldman, L. Tabarovsky & M. Rabinovich, Geophysics, 59(6), 1994, pp 889-901.
SITE INVESTIGATIONS:GEOPHYSICS
951126 Towards an improved seismic imaging technique for crustal structures: the Lithoprobe Sudbury experiment B. Milkereit, D. J. White & A. G. Green, Geophysical Research Letters, 21(10), 1994, pp 927-930. Under the Canadian Lithoprobe program, conventional low(10-55 Hz) and high-frequency (30-140 Hz) vibroseis reflection surveys were conducted across the Sudbury Structure. The main objective of the study was to evaluate the performance of seismic exploration techniques in a complex, mainly crystalline geological setting. The Sudbury experiment demonstrated that high input frequencies can be preserved through appropriate acquisition and processing procedures. Consequently, the high-frequency seismic data proved capable of imaging complex shallow crustal structures not 'seen' by the conventional low-frequency seismic survey. (from Authors) 951127 Seismic reflectivity of the Sudbury Structure North Range from borehole logs D. J. White & 7 others, Geophysical Research Letters, 21(10), 1994, pp 935-938. Results from borehole geophysical logs, full waveform sonic logs, VSP and laboratory core sample measurements indicate that lithologic variations within the Sudbury Igneous Complex (SIC) and footwall rocks are the primary cause of reflections observed regionally on the multi-channel seismic reflection profiles. The effects of macroscopic fracturing and low-grade alteration on the seismic response are only important to a depth of ,,~320 m. The major lithologic units of the SIC and footwall rocks in the North Range of the Sudbury structure have contrasting physical properties. The contrasting velocities and densities of these units imply that the granophyre/quartz-gabbro contact and the SIC/footwall transition can be mapped regionally using seismic reflection methods. (from Authors)
951128 Three component vertical seismic profiling (VSP) experiment in the Sudbury Basin X. Miao, W. M. Moon, B. Milkereit & C. J. Mwenifumbo, Geophysical Research Letters, 21(10), 1994, pp 939-942. A three component VSP experiment was carried out in the metasedimentary Whitewater group of the Sudbury Structure. Processing of the VSP data focused on velocity analysis, wavefield separation, shear-wave analysis, waveform modelling, hodogram analysis, and integration of surface-seismic and borehole geophysical data. Wavefield separation processing and synthetic VSP modelling resulted in a realistic velocity model and the corridor-stacked compressional section correlates well with the surface seismic reflection data. Besides establishing a direct link between borehole lithologies and surface seismic images, the VSP data, using three component particle motion velocity hodograms, provide an independent estimate of true reflector dip in the subsurface of the Sudbury Structure. (from Authors)
951129 Implications of laboratory electrical measurements on interpretation of EM-surveys and origin of the Sudbury Structure T. J. Katsube & M. Salisbury, Geophysical Research Letters, 21(10), 1994, pp 947-950. Electrical resistivity and effective porosity have been measured for 52 drillcore samples representing major sedimentary and igneous lithologies exposed in the Sudbury Structure (SS). While zones of low resistivity are known to exist in the upper sedimentary formations, rocks at depth arc generally
characterized by high resistivities (104-7 × 104 l'l-m), leaving the source of the deep EM anomaly unexplained. However, samples with low resistivities (7-20 [l-m) have been unexpectedly found in the cores from lower sections of the SS, depths possibly corresponding to that of the EM anomaly. These samples are characterized by low porosities (0.3-0.6%), normal bulk densities (2.78-2.81), and a porphyritic texture with a blackish matrix, suggesting carbon as the likely cause of the low resistivities. (from Authors)
951130 Q~ estimates from spectral ratios and multiple lapse time window analysis: results from an underground research laboratory in granite A. J. Feustel & R. P. Young, Geophysical Research Letters, 21(14), 1994, pp 1503-1506. An experiment to measure quality factor (Q) in-situ was carried out at the Underground Research Laboratory in Manitoba, Canada using the Spectral Ratio technique and a form of the Multiple Lapse Time Window Analysis technique. Results from the Spectral Ratio experiment gave Swave quality factor (QI~) of 114 _+ 18. Based upon the short duration of the first arrival pulses and low scattered wave energy in the signal coda, it is concluded that the Spectral Ratio technique measured the intrinsic attenuation of the rock mass. Further analysis using the more recently developed Multiple Lapse Time Window Analysis gave results for intrinsic QI3 (Q~) of between 85 and 100. Conversely, values for scattering Q~ (Qs) were greater than 800. (from Authors)
951131 The fields from a finite electrical dipole - a new computational approach K. I. Sorensen & N. B. Christensen, Geophysics, 59(6), 1994, pp 864-880. Except for small magnetic dipole sources, all electric and magnetic sources are composed of lengths of straight wire, which may be grounded. If the source-receiver separation is large enough, the composite electrical dipoles may be considered to be infinitely small, and in a 1-D earth model the fields are expressed as Hankel transforms of an input function, which depends only on the model parameters. The theory of fast Hankel transforms is extended to include integrals of Hankel transforms, and a method is devised for calculating the filter coefficients. Unlike the fast Hankel transform, the computation involved in the integrated Hankel transforms is not a true convolution, and so a set of filter coefficients must be calculated for each source-receiver configuration. (from Authors)
951132 Electric study of fracture anisotropy at Falkenberg, Germany S. A. AI Hagrey, Geophysics, 59(6), 1994, pp 881-888. Electric and electromagnetic methods have been applied for mapping subsurface fractures and the directional dependence of in-situ electric parameters at the hot dry rock site at Falkenberg, Germany. This study includes the determination of several anisotropy parameters like the mean, longitudinal and transverse resistivity components, the anisotropy coeffident and the strike angle. (from Author)
951133 On the influence of 3-D structures in the interpretation of transient electromagnetic sounding data M. Goldman, L. Tabarovsky & M. Rabinovich, Geophysics, 59(6), 1994, pp 889-901.