P-wave velocity anisotropy of rocks is often investigated by laboratory methods. The extrapolation of the laboratory results to larger rock units requires comparison with direct field measurements. Physical properties of deep-originated rocks were performed on mantle-derived peridotite from the Ivrea zone (N orthwestern Italy). These rock s were exhumed by tectonic processes during collision orogeny up to the Earth’s surface. The direct surface seismic measurements of elastic waves velocity were realized by means of shallow seismic refraction method on the outcrop of peridotite. The measuring base was about 10 m long. Laboratory seismic anisotropy measurement was realized on rock samples from the same outcrop. The geographically oriented spherical samples with diameter 50 mm were radiated by elastic waves in 132 directions under confining stress from atmospheric level up to 200 MPa. Laboratory and field values of the anisotropy of seismic wave ve locities were compared and different scales of measurements were evaluated. The field measuremen ts used frequency about 1 kHz whereas the laboratory measur ement used 700 kHz radiation. Field measurements proved relatively high value of anisotropy P-wave propagation - 25%, while laboratory experiments only 1.5%. This difference is caused by different reason of anisotropy. Laboratory samples contain only microcraks, which represents nearly continuum with rega rd to ultrasound wave length (11 mm). Rock massif, however, contains beside mickrocraks also cracks with comparable size of applied seismic wave length (10 m)., Jan Vilhelm, Vladimír Rudajev, Roman Živor, Tomáš Lokajíček and Zdeněk Pros., and Obsahuje bibliografické odkazy
The research in question deals with problems of determining seismic P- and S-wave velocities for purposes of computing the elastic constants of a rock massif. This experimental study indicates various ways of measurement and its processing for different geological conditions. The experimental measurements were carried out on the surface of the studied rock massif, on the walls in workings, as well as on the surface in a quarry. The question of seismic pick-ups, geophones or piezo-electric transducers and the number of components required to identify P- and S-waves, is discussed. This is considered in connection with the choice and properties of the impact or piezo-electric seismic source. The result is a number of generalizing recommendations with respect to the measuring technique, inclusive of its use for determining the directional dependence of the elastic moduli., Roman Živor, Jan Vilhelm, Vladimír Rudajev and Tomáš Lokajíček., and Obsahuje bibliografii
Various geotechnical tasks require the knowledge of rock properties, e.g., of elastic moduli, fracture systems, inhomogeneities, etc. Seismic measurements usually provide these parameters. To describe the detailed properties of small rock volumes, it is necessary to use high-frequency signals and suitable registration systems. Seismic measurements are carried out directly on rock surfaces. Although the conditions, under which measuremen ts are carried out, seem to be simple and convenient, practical measurements themselves are often complicated. The various measuring systems, including seismic sources and seismic receivers used for different base lengths, are discussed in this paper. It was found that, for the repeatability of measurements, the fixing of the sensors with plaster plays most significant role. Repeatability of hammer blow as seismic source is adversely affected namely by signal amplitude triggering. Pencil lead breaking tests with lead 1 and 6 mm in diameter were found as suitable for testing of the hi gh-frequency measuring systems. Measuring directly on the rock massif surface is different compared to exploration seismic measurements. Due to absence of a low-velocity layer it necessary to use a special choice of mutual orientation of sources and receivers. Polarization analysis may be advantageous to identify the arrival of P and S seismic waves. It was also found that the rock massif behaves as a narrow frequency-b and pass filter. For exciting frequencies of 0.1 and 1 MHz the transmitted signal displayed the same frequency of 25 kHz at a distance of 1.1 m., Jan Vilhelm, Vladimír Rudajev, Roman Živor and Tomáš Lokajíček., and Obsahuje bibliografické odkazy
Modal composition and grain-size characteri stics, physical and mechanical propertie s of three samples of Archean gneisses of the Kola series from the depths of 6.8 to 8.4 km of the Kola Superdeep Borehole (KSDB-3) and two collections of their surface analogues were analysed. On the basis of a comparison of the petrographic characteristics of the borehole samples and analogues, it was found that not all analogues are equivalents of corresponding core samples completely. Mechanical properties of core samples are affected by depth of the core sample position in the borehole. This work forms part of the research in the frame of the INTAS Project No.314 "Geodynamics in the cross-section of the Kola superdeep"., Jiřina Trčková, Vladimír Šrein, Martin Šťastný and Roman Živor., and Obsahuje bibliografické odkazy