Ultrasonic velocity and attenuation of longitudinal waves in rocks

Hughes' pulse technique for measuring longitudinal velocities has been adapted and extended to measure attenuation of longitudinal waves in the frequency range from 250 to 1000 kc/s. Data for velocity and attenuation in eight different rocks (three granites, one porphyry, two sandstones, one limestone, and one marble) are given at eight different frequencies ranging from 250 to 1000 kc/s. The values of attenuation measured have been found to be much higher than for metals and plastics in the same frequency range. They lie between 1 and 37 decibels per centimeter. All of the curves of attenuation versus frequency show one or several peaks, none of the curves indicating a marked law of increase or decrease of attenuation with frequency. In one granite, in the limestone, and in the marble successive peaks occur at harmonic frequencies. A comparison between the wavelengths for which the peaks occur and the grain size of the rocks shows a good agreement for the coarse-grained rocks between the frequencies of occurrence of the peaks and the resonance frequencies of the largest crystals of the rocks, indicating a very large effect of the frictional boundary losses on attenuation when the wavelength approaches the grain size of the rock.