We measured waveform peak amplitudes for the various samples, as discussed in the procedural section. The ¶ and § amplitudes attenuated by a factor of about 2.5 from the source-receiver delay time measurement, to the stainless-steel plug measurement. This decay is probably due mostly to poor coupling, and some relatively small attenuation due to intrinsic Q, since the plug was only 1.187 inches long and made of the same material as the source-receiver transducer clamping apparatus.
We made similar measurements on the wet and dry Massillon Sandstone rock samples. The ¶-wave amplitude attenuated about a factor of 2.5 from dry to wet. In light of the stainless-steel result, this implies that the attenuation due to coupling and Q are not that different from that of stainless steel. However, the §-wave amplitude attenuated a factor of 15 from dry to wet, indicating a significant intrinsic Q-attenuation component. Intuitively, this might be explained as shear stresses being more efficient at ``squirting'' fluid through the available pore spaces, hence losing energy to friction heat-loss and the work required to permanently displace the fluid to a non-equilibrium position. This result could also be explained as destructive interference from ¶-§ conversions and diffractions attenuating the direct § arrival. Finally, these amplitude measurements were made on one peak of the waveform. Attenuation would be more accurately studied by examining the amplitude frequency response by Fourier Transform spectral techniques over a more complete direct arrival waveform time series.