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Surveys in Geophysics

, Volume 15, Issue 5, pp 443–465 | Cite as

The influence of dry and water saturated cracks on seismic velocities of crustal rocks - A comparison of experimental data with theoretical model

  • T. Popp
  • H. Kern
Article

Abstract

The pressure dependence of P- and S-wave velocities, velocity anisotropy, shear wave splitting and crack-porosity has been investigated in a number of samples from different crustal rock types for dry and wet (water saturated) conditions. At atmospheric pressure, P-wave velocities of the saturated, low-porosity rocks (< 1%) are significantly higher than in dry rocks, whereas the differences for S-wave velocities are less pronounced. The effect of intercrystalline fluids on seismic properties at increased pressure conditions is particularly reflected by the variation of the Poisson's ratio because P-wave velocities are more sensitive to fluids than S-wave velocities in the low-porosity rocks. Based on the experimental data, the respective crack-density parameter (ε), which is a measure of the number of flat cracks per volume unit contained within the background medium (crack-free matrix), has been calculated for dry and saturated conditions. There is a good correlation between the calculated crack-densities and crack-porosities derived from the experimentally determined volumetric strain curves. The shear wave velocity data, along with the shear wave polarisation referred to a orthogonal reference system, have been used to derive the spatial orientation of effective oriented cracks within a foliated biotite gneiss. The experimental data are in reasonable agreement with the self consistent model of O'Connell and Budiansky (1974). Taking the various lithologies into account, it is clear from the present study, that combined seismic measurements ofV p andV s , using theV p V s -ratio, may give evidence for fluids on grain boundaries and, in addition, may provide an estimate on the in-situ crack-densities.

Key words

Crustal rocks seismic properties pore fluid saturation crack-porosity aspect ratio poisson's ratio modelling of the elastic behaviour 

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References

  1. Berge, P.A., Fryer, G.J., and Wilkens, R.H.: 1992, ‘Velocity-Porosity Relationships in the Upper Oceanic Crust: Theoretical considerations’,J. Geophys. Res. 97, 15239–15254.Google Scholar
  2. Birch, F.: 1961, ‘The Velocities of Compressional Waves in Rocks to 10 kb, Part 2’,J. Geophys. Res. 66, 2199–2224.Google Scholar
  3. Cheng, H., C. and Toksöz, M.N.: 1979: ‘Inversion of Seismic Velocities for the Pore Aspect Ratio Spectrum of a Rock’,J. Geophy. Res. 84, 7533–7543.Google Scholar
  4. Christensen, N.I.: 1965, ‘Compressional Wave Velocities in Metamorphic Rocks at Pressures to 10 kbar’,Geophys. Res. 70, 6147–6164.Google Scholar
  5. Christensen, N.I.: 1984, ‘Pore Pressure and Ozeanic Crustal Seismic Structure’,Geophysical J. Roy. Astr. Soc. 79, 411–424.Google Scholar
  6. Crampin, S.: 1987, ‘Geological and Industrial Implications of Extensive-Dilatancy Anisotropy’,Nature 328, 491–496.Google Scholar
  7. Dürbaum, H.J.; Reichert, Ch.; Sadowiak, P. and Bram, K. (eds.): ‘Integrated Seismics Oberpfalz 1989’,KTB report, 92-5.Google Scholar
  8. Falls, S.D., Young, R.P., Carlson, S.R. and Chow, T.: 1992, ‘Ultrasonic Tomography and Acoustic Emission in Hydraulically Fractured Lac du Bonnet Grey Granite’,J. Geophys. Res. 97, 6867–6884.Google Scholar
  9. Fountain, D.M. and Christensen, N.I.: 1989, ‘Composition of the Continental Crust and Upper Mantle; A Review’, in: Pakister, L., Mooney, W. (eds.),Geophysical framework of the United States Geological Soc. Am., 711–742Google Scholar
  10. Heinicke, F. and Vollbrecht, A.: 1988, ‘Gefügestudien an Graphitquarziten im moldanubisch-saxothuringischen Übergangsbereich, NE-Bayern’,Erlanger geol. Abh. 116, 35–40.Google Scholar
  11. Holbrook, W.S., Mooney, W.D. and Christensen, N.I.: 1992, ‘The Seismic Velocity Structure of the Deep Continental Crust’, in: D.M. Fountain, R. Arculus and R.W. Kay (eds.),Developments in Geotectonics 23, Elsevier, 1–44.Google Scholar
  12. Hudson, J.A: 1981, ‘Wave Speeds and Attenuation of Elastic waves in Materials Containing Cracks’,Geophys. J. R. Astron. Soc. 64, 133–150.Google Scholar
  13. Kern, H.: 1990, ‘Laboratory Seismic Measurements: an aid in the Interpretation of Seismic Field Data’,Terra Nova 2, 617–628Google Scholar
  14. Kern, H.: 1982, ‘P-and S-Wave Velocities in Crustal and Mantle Rocks Under the Simultaneous Action of High Confining Pressure and High Temperature and the Effect of the Rock Microstructure’, in: W. Schreyer (ed.),High Pressure Researches in Geoscience, Schweizerbart, Stuttgart, 15–45.Google Scholar
  15. Kern, H., Popp, T. and Schmidt, R.: 1991, ‘The Velocity and Density Structure of the 4000m Crustal Segment at the KTB-Drilling Site and their Relationship to Lithological and Microstructural Characteristics of the Rock: an Experimental Approach’,Scientific drilling 2, 130–145.Google Scholar
  16. Kern, H., Popp, T. and Schmidt, R. (this volume). ‘The Effect of a Deviatoric Stress on Physical Rock Properties. - An Experimental Study Simulating the In-situ Stress Field at the KTB Drilling Site, Germany’.Google Scholar
  17. Lüschen, E., Söllner, W., Horath, A. and Rabbel, W.: 1990, ‘Integrated P- and S-Wave Boreehole Experiments at the KTB Deep Drilling Site’,KTB report 90-6b, 85–136.Google Scholar
  18. Lüschen, E., Sobolev, S., Werner, U., Söllner, W. and Hubral, P.: 1993, ‘Fluid/Gas Reservoir (?) Beneath the KTB Drillbit Indicated by Seismic Shear-Wave Observations’,Geophys. Res. Lett. 20, 923–926.Google Scholar
  19. Marquis, G. and Hyndman, R.D.: 1992, ‘Geophysical Support for Aqueous Fluids in the Deep Crust: Seismic and Electrical Relationships’.Geophys. J. Int. 110, 91–105.Google Scholar
  20. Nur, A.: 1972, ‘Dilatancy, Pore Fluids, and Premonitory Variations of ts/tp Travel Times’,Bull. seis. Soc. Am. 62, 1217–1222.Google Scholar
  21. Nur, A. and Simmons, G.: 1969, ‘The Effect of Saturation on Velocity in Low Porosity Rocks’,Earth Planet. Sci. Lett. 7, 183.Google Scholar
  22. O'Connell, R.J. and Budiansky, B.: 1974, ‘Seismic Velocities in Dry and Saturated Cracked Solids’,J. Geophys. Res. 86, 5412–5425.Google Scholar
  23. Popp, T. and Kern, H.: 1993, ‘Thermal Dehydration Reactions Characterized by Combined Measurements of Electrical Conductivity and Elastic Wave Velocities’,Earth Planet Sci. Lett. 120, 43–57.Google Scholar
  24. Rabbel, W.: 1992, ‘Seismic Anisotropy at the KTB Drilling Site’,KTB-Report 92-5, 275–290.Google Scholar
  25. Sayers, C.M.: 1993, ‘Comment on “Crack Models for a Transversely Isotropic Medium”’,J. Geophys. Res. 98, 14211–14213.Google Scholar
  26. Siegesmund, S., Kern, H. and Vollbrecht, A.: 1991, ‘The Effect of Oriented Microcracks on Seismic Velocities in an Ultramylonite’,Tectonophysics 186, 241–251Google Scholar
  27. Spencer, J.W. and Nur, A.: 1976, ‘The Effects of Pressure, Temperature, and Pore Water on Velocities in Westerly Granite’,J. Geophys. Res. 81, 899–904Google Scholar
  28. Vernik, L. and Nur, A.: 1992, ‘Petrophysical Analysis of the Cajon Pass Scientific Well: Implications for Fluid Flow and Seismic Studies in the Continental Crust’,J. Geophys. Res. 97, 5121–5134.Google Scholar
  29. Walsh, J.B.: 1965, ‘The Effect of Cracks on the Compressibility of Rocks’,J. Geophys. Res. 70, 381–389.Google Scholar
  30. Wenzel, F. and Sandmeier, K.-J.: 1992, ‘Geophysical Evidence for Fluids in the Crust Beneath the Black Forest, SW Germany’,Earth-Sci. Rev. 32, 61–75.Google Scholar
  31. Yukutake, H.: 1989, ‘Fracturing Process of Granite Inferred from Measurements of Spatial and Temporal Variations in Velocity During Triaxial Deformation’,J. Geophys. Res. 94, 15639–15651.Google Scholar

Copyright information

© Kluwer Academic Publishers 1994

Authors and Affiliations

  • T. Popp
    • 1
  • H. Kern
    • 1
  1. 1.Mineralogisch-Petrographisches InstitutKielGermany

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