P – AND SV – WAVES FROM UPHOLE SHOOTING*

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Abstract
Uphole recordings in sediments very often reveal shear waves. With their velocity and that of the P‐waves Poisson's ratio may be determined, this usually has unexpectedly high values.A number of up‐hole shots were recorded with a linear spread of geophones and with constant gain amplifiers. Calculations were made to show the effect of the free surface and ray divergence (the spread factor). The theoretical, relative amplitudes of the ground motion were plotted together with the observed values. In general, there is good agreement between theory and observation which is better for the P‐waves than for the S‐waves. The reasons for this difference are discussed.Finally, an absorption coefficient is calculated from the amplitudes measured at the surface.

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