An analysis is presented of the diffraction by a hydraulically induced crack of time-harmonic signals emitted by a point source. Both diffraction by an empty crack and diffraction by a fluid-filled crack are considered. It is assumed that the crack is plane and of circular shape. The analysis is based on elastodynamic ray theory, which yields relatively simple approximations to the diffracted fields if ω a/cL is sufficiently larger than unity, where ω is the circular frequency of the incident waves, a is the radius of the crack, and cL is the velocity of longitudinal waves. The diffracted fields include direct diffractions from the crack edges as well as diffractions of signals which travel via the crack faces. The relative magnitudes of these various contributions have been plotted. For three positions of the point of observation, numerical results for the three displacement components have been displayed in graphs.

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