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The application of seismic velocity tomograpgy in geotechnical investigations
310A
SITE 1NVESTIGATIONS:GEOPHYSICS
accommodated by shear in the vertical plane normal to the faults and displacement transfer accommodated by shear in the fault parallel plane. (from Authors) 967152 On the formation of a recent, small fracture in a phosphate mine - Nahal Zin, Israel Y. Eyal, Y. Hatzor & A. Eyal, Israel Journal of Earth Sciences, 44(2), 1995, pp 11 l-l 14. The paper presents some observations on a fracture zone formed recently in the eastern part of the northern Negev, Israel. The study area is located within the Zin syncline, which is part of the Syrian Arc fold system. This is an asymmetric syncline found between the Hazera monocline and Mahmal anticline, 10 km west of the Dead Sea rift valley margins. The folds in this area, mainly monoclines and asymmetric synclines, initiated in the Upper Cretaceous and continued developing at least to the Middle Miocene or Pliocene. These monoclines were formed by displacement along reverse faults, as evidenced by repetitions of the stratigraphic sequence in boreholes drilled in five monoclinal crests and interpretation of seismic profiles. The stress field under which these folds were formed, Snmax trending WNW-ESE and Shin trending NNE-SSW, has been called the Syrian Arc stress field. (from Authors)
Geophysical
techniques
967153 Evaluation of permeable fractures by multi-offset hydrophone vertical seismic profiling (VSP) T. Kiguchi, H. Ito, Y. Kuwahara, S. Nakao & D. T. Ohminato, Geothermal Science & Technology, 5(1-2), 1995, pp 21-29. A high frequency multi-offset hydrophone VSP experiment was carried out in the shallow wells drilled at the Fracture Evaluation Test site in Iidate, Fukushima prefecture, Japan in order to detect permeable fractures intersecting the borehole and to characterize them. Tube waves are observed at several depths. Fracture dip, strike and permeability were calculated from the amplitude ratio of tube wave to P-wave. The analysis is based on the model that tube waves are generated when the incident P-wave compresses the fractures intersecting wellbore. With tube wave analysis it is possible to distinguish permeable fractures from impermeable fractures observed by borehole imaging tools. It is concluded that the low dip angle fracture is permeable on the basis of the tube wave analysis. This is consistent with the flow properties of the fractures estimated from the circulation test. (from Authors) 967154 The application of seismic velocity tomography in geotechnical investigations V. S. Hope, Proceedings - ICE: Geotechnical Engineering, 113(4), 1995, pp 215225. Seismic velocity tomography is a potentially valuable tool in geotechnics, but there are certain situations where it is not an appropriate method. Fortunately, before going on site it is possible to assess whether this relatively costly technique can provide useful information. This paper describes the theory of seismic tomography and highlights the possible difficulties of the method. The factors which should be considered when evaluating the effectiveness of tomography at a site are summarized. (Author) 967155 Water log D. Parker, New Civil Engineering (NCE), 1159,1996, pp 4041. This article describes the electrokinetic surveying (EKS) technique applied to the detection and monitoring of groundwater resources. The technique detects electrical signals generated by water in response to a seismic impulse.
Separating signals from background noise has always been a problem. How, however, geophysical consultancy GroundFlow has developed a kit using high quality audio components which has overcome this problem. With no previous ground condition information, it can locate an aquifer within 20 minutes. A proper survey takes four or five days and costs around 1% of the cost of an equivalent borehole survey. Success rates of finding exploitable aquifers are over 90%. The EKS technique has other potential applications in mining, civil engineering and pollution control. (J.M.McLaughlin) 967156 On multifrequency shielding behaviour of cylindrical overburden covering concentric elongated ore deposits D. I. Nagubai & P. D. Saraf, Acta Geophysics Polonica, 43(l), 1995, pp 63-74. Low-frequency EM shielding sensitivity of surrounding conducting formations, covering (non-galvanically) concentric elongated ore deposits, has been analysed theoretically. The model consists of a two shell composite cylindrical system having different electrical and magnetic properties in the outer and inner shells. Shielding equations have been derived and some representative numerical results have been obtained. The study may find relevance in analyzing possible effects (either adverse or favourable) of the overlying structures on low frequency EM shielding and also in delineating the covered conducting ore deposits by conventional geoelectromagnetic techniques. (from Authors) 967157 Detection of underground cavities with monofrequency electromagnetic tomography between boreholes in the frequency range 100 MHz to 1 GHz P. Cote, P. Degauque, R. Lagabrielle & N. Levent, Geophysical Prospecting, 43(S), 1995, pp 1083-l 107. In order to detect underground cavities, a geophysical method based on the interaction of a monochromatic electromagnetic wave in the frequency band 100 MHz to 1 GHz with the ground situated between two boreholes was developed. The equipment involved and its operation is quite simple: the surface devices are commercially available and only the transmitter and receiver antennae must be specially built. The method is shown to be quite efficient and its cost should be reasonably low. (from Authors) 967158 Geotomografla eletromagnetica (Electromagnetic geotomography) E. P. Lopes & E. P. Lopes, Revista Brasileira de Geofsica, 12(2), 1994, pp 163-175. An electromagnetic method is proposed in this work. It reconstructs images of the distributions of the electrical conductivity and dielectric permittivity from phase-shift measurements of electromagnetic waves that criss-cross the scanned medium. Some of the applications are: monitoring of enhanced oil recover processes, site characterization for the installation of chemical or nuclear waste repositories, and definition of the location and extent of grout injected into the ground for civil engineering purposes. (from English summary) 967159 Making use of the low velocity zone (LVZ) in hydrogeology and engineering geology T. Kryniclci, Kwartalnik Geologiczny, 39(4), 1995, pp 513526. Analysis of the results of low velocity zone (LVZ) measurements indicates that they can be used in both hydrogeology and engineering geology. The results of LVZ measurements allow calculation to be made of the aeration zone, wave velocity within the zone and its base. as well as water table contiguration. (Author)
SITE 1NVESTIGATIONS:GEOPHYSICS
accommodated by shear in the vertical plane normal to the faults and displacement transfer accommodated by shear in the fault parallel plane. (from Authors) 967152 On the formation of a recent, small fracture in a phosphate mine - Nahal Zin, Israel Y. Eyal, Y. Hatzor & A. Eyal, Israel Journal of Earth Sciences, 44(2), 1995, pp 11 l-l 14. The paper presents some observations on a fracture zone formed recently in the eastern part of the northern Negev, Israel. The study area is located within the Zin syncline, which is part of the Syrian Arc fold system. This is an asymmetric syncline found between the Hazera monocline and Mahmal anticline, 10 km west of the Dead Sea rift valley margins. The folds in this area, mainly monoclines and asymmetric synclines, initiated in the Upper Cretaceous and continued developing at least to the Middle Miocene or Pliocene. These monoclines were formed by displacement along reverse faults, as evidenced by repetitions of the stratigraphic sequence in boreholes drilled in five monoclinal crests and interpretation of seismic profiles. The stress field under which these folds were formed, Snmax trending WNW-ESE and Shin trending NNE-SSW, has been called the Syrian Arc stress field. (from Authors)
Geophysical
techniques
967153 Evaluation of permeable fractures by multi-offset hydrophone vertical seismic profiling (VSP) T. Kiguchi, H. Ito, Y. Kuwahara, S. Nakao & D. T. Ohminato, Geothermal Science & Technology, 5(1-2), 1995, pp 21-29. A high frequency multi-offset hydrophone VSP experiment was carried out in the shallow wells drilled at the Fracture Evaluation Test site in Iidate, Fukushima prefecture, Japan in order to detect permeable fractures intersecting the borehole and to characterize them. Tube waves are observed at several depths. Fracture dip, strike and permeability were calculated from the amplitude ratio of tube wave to P-wave. The analysis is based on the model that tube waves are generated when the incident P-wave compresses the fractures intersecting wellbore. With tube wave analysis it is possible to distinguish permeable fractures from impermeable fractures observed by borehole imaging tools. It is concluded that the low dip angle fracture is permeable on the basis of the tube wave analysis. This is consistent with the flow properties of the fractures estimated from the circulation test. (from Authors) 967154 The application of seismic velocity tomography in geotechnical investigations V. S. Hope, Proceedings - ICE: Geotechnical Engineering, 113(4), 1995, pp 215225. Seismic velocity tomography is a potentially valuable tool in geotechnics, but there are certain situations where it is not an appropriate method. Fortunately, before going on site it is possible to assess whether this relatively costly technique can provide useful information. This paper describes the theory of seismic tomography and highlights the possible difficulties of the method. The factors which should be considered when evaluating the effectiveness of tomography at a site are summarized. (Author) 967155 Water log D. Parker, New Civil Engineering (NCE), 1159,1996, pp 4041. This article describes the electrokinetic surveying (EKS) technique applied to the detection and monitoring of groundwater resources. The technique detects electrical signals generated by water in response to a seismic impulse.
Separating signals from background noise has always been a problem. How, however, geophysical consultancy GroundFlow has developed a kit using high quality audio components which has overcome this problem. With no previous ground condition information, it can locate an aquifer within 20 minutes. A proper survey takes four or five days and costs around 1% of the cost of an equivalent borehole survey. Success rates of finding exploitable aquifers are over 90%. The EKS technique has other potential applications in mining, civil engineering and pollution control. (J.M.McLaughlin) 967156 On multifrequency shielding behaviour of cylindrical overburden covering concentric elongated ore deposits D. I. Nagubai & P. D. Saraf, Acta Geophysics Polonica, 43(l), 1995, pp 63-74. Low-frequency EM shielding sensitivity of surrounding conducting formations, covering (non-galvanically) concentric elongated ore deposits, has been analysed theoretically. The model consists of a two shell composite cylindrical system having different electrical and magnetic properties in the outer and inner shells. Shielding equations have been derived and some representative numerical results have been obtained. The study may find relevance in analyzing possible effects (either adverse or favourable) of the overlying structures on low frequency EM shielding and also in delineating the covered conducting ore deposits by conventional geoelectromagnetic techniques. (from Authors) 967157 Detection of underground cavities with monofrequency electromagnetic tomography between boreholes in the frequency range 100 MHz to 1 GHz P. Cote, P. Degauque, R. Lagabrielle & N. Levent, Geophysical Prospecting, 43(S), 1995, pp 1083-l 107. In order to detect underground cavities, a geophysical method based on the interaction of a monochromatic electromagnetic wave in the frequency band 100 MHz to 1 GHz with the ground situated between two boreholes was developed. The equipment involved and its operation is quite simple: the surface devices are commercially available and only the transmitter and receiver antennae must be specially built. The method is shown to be quite efficient and its cost should be reasonably low. (from Authors) 967158 Geotomografla eletromagnetica (Electromagnetic geotomography) E. P. Lopes & E. P. Lopes, Revista Brasileira de Geofsica, 12(2), 1994, pp 163-175. An electromagnetic method is proposed in this work. It reconstructs images of the distributions of the electrical conductivity and dielectric permittivity from phase-shift measurements of electromagnetic waves that criss-cross the scanned medium. Some of the applications are: monitoring of enhanced oil recover processes, site characterization for the installation of chemical or nuclear waste repositories, and definition of the location and extent of grout injected into the ground for civil engineering purposes. (from English summary) 967159 Making use of the low velocity zone (LVZ) in hydrogeology and engineering geology T. Kryniclci, Kwartalnik Geologiczny, 39(4), 1995, pp 513526. Analysis of the results of low velocity zone (LVZ) measurements indicates that they can be used in both hydrogeology and engineering geology. The results of LVZ measurements allow calculation to be made of the aeration zone, wave velocity within the zone and its base. as well as water table contiguration. (Author)