Effects of attenuation on reflections: Experimental test

A well-known effect of seismic wave attenuation is the change in frequency content and amplitude of a pulse propagating through a lossy medium. A related aspect of wave propagation in lossy media is the frequency dependence of the reflection coefficients. This phenomenon is studied here experimentally and by computer simulation. It is found that attenuation contrast has a relatively large effect on reflections when the acoustic impedance (i.e., density times velocity) difference of the two media is small. While this is a common situation in the upper crust of the earth, very low acoustic impedance contrast is difficult to create in the laboratory. By using carefully chosen samples of polymer and silicon rubber, we show that with low acoustic impedance contrast and high attenuation contrast, an increase in the amplitude of reflections due to Q contrast is observable. We also show that there is no observable phase effect due to the attenuation contrast. By measuring and simulating the reflected signals at angles of incidence to 30°, we find that the Q contrast effect is important only at small angles and that it dies out at large ones.