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The 8th International Symposium on Recent Advances in Exploration Geophysics (RAEG 2004)

  • Conference date: 10 Mar 2004 - 10 Mar 2004
  • Location: Kyoto, Japan
  • Published: 10 March 2004
7 results

    • Permittivity Measurement Using Borehole Radar from Single Hole

      https://doi.org/10.3997/2352-8265.20140055

      This paper provides a method for measuring permittivity using borehole radar from single hole. First we use numerical simulation to examine the suitability of borehole radar for measuring relative permittivity from single hole. We introduce a 2-D pseudospectral time domain (PSTD) algorithm that allows us to model the full EM wavefield for rotationally symmetric structure. The effect of the borehole mud and the response of surrounding formation are simulated. lt is found that the relative permittivity logging curve is sensitive to the formation interface of surrounding formation. The simulation results show that the measured relative permittivity is closed to the true parameters of the surrounding formation. We processed field data using a variance fractal dimension technique that can detect coherent borehole radar signal from background noise. The measured relative permittivity logging curve could be useful for identifying formation type and detecting water-bearing property.

    • Temporal Variation in Shear Wave Anisotropy Detected with ACROSS

      Authors R. Ikuta and K. Yamaoka
      https://doi.org/10.3997/2352-8265.20140056

      We are now developing a seismic exploring system named ACROSS aiming at detection of temporal variation in elastic properties of the crust. We made an experiment lasting for 15 months, from January 2000 to April 2001 at a site near the Nojima fault, which ruptured during the 1995 Kobe earthquake (Mw7.2). Elastic waves generated by surface-deployed ACROSS sources were received with seismometers deployed in the bottom of 800m- and 1700m-deep boreholes near the sources. During the experiment, sudden delays in travel time for S wave were observed at the time when the 2000 Western-Tottori earthquake (Mw6.6) and the 2001 Geiyo earthquake (Mw6.7) occurred. The traveltimes of the S wave abruptly delayed and gradually recovered associated with each earthquake with little change in that of P waves. The delay was about 0.4% and 0.1% of absolute travel time for the Western-Tottori earthquake and Geiyo earthquake, respectively. The delays were polarized in a direction perpendicular to the Nojima fault for both cases. This suggests that the density of the cracks parallel to the fault increased associated with the earthquakes. These cracks can be regarded as being opened by an increase of pore-pressure. An additional experiment determining the static structure revealed that the preferred orientation of the cracks had existed and be enhanced with the strong shaking of the earthquakes in middle distance.

    • Pseudo Three-Dimensional Refraction Method for Rock Bed Detection

      https://doi.org/10.3997/2352-8265.20140057

      Refraction tomography nowadays has developed to unveil 3 dimensional structures of subsurface. Delineation of a rock bed which usually happens to be one of the main purpose of a survey in most engineering sites, however, is not easy because inversions usually produce images of gradual change of the material properties. From the survey designed for 3 dimensional refraction data acquisition, we can get the contours of first arrivals of a shot on the surface by applying an interpolation such as kriging. Re-sampling first arrivals form these contours, we get reciprocal traveltime curves between two shots respectively. Then, we applied the generalized reciprocal method (Palmer, 1982) using these data finally to get a pseudo 3 dimensional subsurface structure.

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