Rayleigh channel waves for the in-seam seismic detection of discontinuities

Abstract

Two-dimensional seismic models are used to reproduce the geological sequence cheek-seam-cheek in deep coal mines. The known reflection method based on Rayleigh channel waves is investigated with respect to discontinuities being composed of a termination of the seam and a fractured zone outside the seam. By means of fractured zones having different reflection coefficients discontinuities are designed representing clay hogs or microtectonic faults. Results obtained by investigating amplitudes, frequencies and phase velocities show a strong increase of the rate of amplitude decay with decreasing phase velocity. Furthermore it is demonstrated that the part of the Rayleigh channel wave propagating outside the seam is responsible for the detectability of a discontinuity. Expressing the detectability numerically the ratio E_R of the channel wave's energy inside the seam to its total energy has been used. The value 0.5 for E_R is derived to be a standard value for distinguishing the phase velocity range for which reliable reflection surveys are possible (E_R > 0.5) or not (E_R < 0.5).

          ARK: https://n2t.net/ark:/88439/y015755

Permalink: https://geophysicsjournal.com/article/107