The evanescent wave in Cagniard's problem for a line source generating SH waves

Using the Cagniard-de Hoop method we derive the particle velocity from an impulsive line source for transmitted SH waves through a boundary separating two homogeneous and solid half-spaces. With a series of examples the properties of the evanescent wave are displayed as they would be recorded on a velocity transducer. It is shown that these waves should be prominent when either the source or the receiver is in the proximity of a boundary across which the acoustic impedance changes significantly. The amplitude decay of waves from a line source with distance far from the interface agrees well with the rate predicted by the asymptotic theory. -from Authors