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The motion of a geophone case placed on the surface of an elastic earth does not follow faithfully the motion of the earth at high frequencies. In effect, a weight placed on the surface of an elastic solid constitutes a damped oscillating system. The elastic restoring forces are determined by the area of contact between the weight and the surface of the solid and by the elastic moduli of the solid. The damping force is due to emission of elastic waves by the oscillating weight. The motion of the solid also contributes to the inertia of the system. Equations are developed for these forces on the assumption that the wave length is long compared to the linear dimensions of the area of contact between the weight and the elastic solid. This leads to a determination of the frequency of oscillation and of the decrement of such a system.

Elastic waves are reflected not only from discontinuities in the medium in which they are propagated, but also from transition layers in which the elastic constants are continuous functions of position; the coefficient of reflection is then a function of wave length. Section 1 of this paper gives explicit formulae for the coefficient of reflection of continuous waves from such a layer, at vertical incidence. In Section 2 the manner of variation of the coefficient of reflection with the angle of incidence is discussed qualitatively. Finally, in Section 3, the shape of a pulse reflected from a transition layer is determined.

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