Estimation of the rocks statistical parameters from traveltime measurements |
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Authors: | A Kaslilar YuA Kravtsov SA Shapiro S Buske R Giese Th Dickmann |
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Institution: | 1. Mining Faculty, Department of Geophysics, Istanbul Technical University, 34390, Maslak, Istanbul, Turkey 2. Institute of Physics, Maritime University in Szczecin, Waly Chrobrego 1/2, 70500, Szczecin, Poland 3. Space Research Center, Polish Academy of Sciences, 00716, Warsaw, Poland 4. Fachrichtung Geophysik, Freie Universit?t Berlin, Malteserstr. 74-100, Haus D, 12249, Berlin, Germany 5. Department of Rock Mechanics and Lithostatics, GFZ Potsdam, Germany 6. Amberg Measuring Technique AG, Zurich, Switzerland
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Abstract: | In this paper the method for estimating the statistical parameters of the medium from traveltime measurements of refracted
waves is applied to study the statistical characteristics of crystalline rocks at the Multifunctional Station Faido (Gotthard
Base Tunnel, Switzerland). The method is based on the geometrical optics (GO) approximation. A covariance function for traveltime
fluctuations has been obtained by considering quasihomogeneous fluctuations of sound velocity in a plain-stratified medium.
Strongly anisometric (having unequal dimensions in different directions) random inhomogeneities were embedded in this medium.
To estimate the statistical parameters around the tunnel, the traveltime fluctuations are calculated. It is assumed that each
observation of traveltime-distance relation for a given shot-receiver group corresponds to a particular realization of a medium
statistical ensemble. By calculating the variance and the zero cross intervals of the first derivative of traveltime fluctuations,
the standard deviation of the velocity fluctuations and the characteristic horizontal scale of the inhomogeneities are estimated.
Although the method allows to obtain the characteristic lengths of the inhomogeneities in vertical as well as in horizontal
direction, the limited offset of the field data made it only possible to measure the latter. The estimated horizontal characteristic
scale is about 13 m, which is reasonably close to the direct geological measurements in the studied region, where quartz lenses
are dominant among the inhomogeneities. The standard deviation of the velocity is estimated as 4.5%, which might be caused
by the fractured structure around the tunnel and also by the fault zone near the study area. |
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Keywords: | random media geometrical optics traveltime fluctuations refracted waves Gotthard Base Tunnel |
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