Attenuationin the earth appreciably affects the usefulness of seismic waves in geological studies. It limits the distance over which the waves can be transmitted and it is the major factor in determining the frequency band of the useful energy. Variation of attenuation with frequency is assumed to be responsible for wave form distortion, thus complicating the interpretation of seismic data. Attenuation has also been suspected of influencing propogation velocities. For these reasons, we have undertaken a series of experiments to verify the reports of others as well as to investigate questions which have not been touched by others. The approach has been wholly experimental -that is to say, we have tried only to describe the phenomenon in question. The region of cretaceous shale outcrops in eastern Colorado was chosen for the site of the experiments. This region also served Dr. Ricker in a similar work which he has previously reported. In this area, the outcropping Pierre shale is approximately 4000 feet thick and exceptionally uniform. The largest variation in the 7oo-foot section used represents a reflection coefficient of only 4/100. For vertical travel, the average compressional velocity was measured to be 7100 feet/second and the average shear velocity 2630 feet/second. For horizontal travel at a depth of 500 feet, the corresponding velocities were 7360 and 2680 feet/second, respectively.The most consistent and dependable results were obtained with compressional waves from dynamite explosions. Charges were fired in shot holes and consisted of boosters, one pound of dynamite, or ten pounds. In order to obtain vertically travelling shear waves, we used a horizontally swinging mass of 2000 pounds that was caused to strike a concrete block anchored into the earth. Satisfactory wave forms were not obtained however. On the other hand, satisfactory horizontally travelling waves were produced by the impact of a zoo-pound mass on the bottom of a shot hole.

Attenuation measurements were made near Limon, Colorado, where the Pierre shale is unusually uniform from depths of less than 100 ft to approximately 4,000 ft. Particle velocity wave forms were measured at distances up to 750 ft from explosive and mechanical sources. Explosives gave a well‐defined compressional pulse which was observed along vertical and horizontal travel paths. A weight dropped on the bottom of a borehole gave a horizontally‐traveling shear wave with vertical particle motion. In each case, signals from three‐component clusters of geophones rigidly clamped in boreholes were amplified by a calibrated, wide‐band system and recorded oscillographically. The frequency content of each wave form was obtained by Fourier analysis, and attenuation as a function of frequency was computed from these spectra. For vertically‐traveling compressional waves, an average of 6 determinations over the frequency range of 50–450 cps gives α=0.12 f. For horizontally‐traveling shear waves with vertical motion in the frequency range 20–125 cps, the results are expressed by α=1.0 f. In each case attenuation is expressed in decibels per 1,000 ft of travel and f is frequency in cps. These measurements indicate, therefore, that the Pierre shale does not behave as a visco‐elastic material.

The velocities of elastic waves in a laminated medium have been determined by calculating the effective elastic parameters and the effective density. The procedure is to assume the medium to be in static equilibrium and exposed to certain stresses. The stresses are of such a nature as to generate strains similar to those which would exist during the passage of an elastic wave through the medium. From the application of Hooke's law, an effective stiffness constant for the medium is obtained. The ratio of this effective stiffness to the effective density is the square of the velocity of the elastic wave. For a medium consisting of layers of two materials with the same density but with a velocity contrast of two (2), the velocity of compressional waves traveling parallel to the layering is 20 percent higher than the velocity of the same wave traveling perpendicular to the layers. The SH shear wave has a velocity which is 25 percent higher than the SV shear wave for the same laminated medium.

The velocity of elastic waves traveling parallel and perpendicular to the layering in a laminated medium has been determined by means of static elasticity. The procedure is to assume the medium to be in static equilibrium and exposed to certain stresses. The stresses are of such a nature as to generate strains similar to those which would exist during the passage of an elastic wave through the medium. From the application of Hooke's law, an effective stiffness constant for the medium is obtained. The ratio of this effective stiffness to the effective density is the square of the velocity of the elastic wave. For a medium consisting of layers of two materials with the same density but with a velocity contrast of two, the velocity of compressional waves traveling parallel to the layering is 20 percent higher than the velocity of the same wave traveling perpendicular to the layers. The SH shear wave has a velocity which is 25 percent higher than the SV shear wave for the same laminated medium.

An experimental investigation of the effect of hydrostatic pressure on cavitation erosion is described. A focusing acoustic system enclosed in a pressure chamber permitted the sound pressure and the hydrostatic pressure to be varied independently over the range of 1–20 atm. The intensity of cavitation, as measured by the erosion rate of aluminum, was found to grow at an increasing rate with hydrostatic pressure. Experimental results obtained in this pressure range correlate with published Russian data taken at pressures up to 75 atm. A correspondence between cavitation erosion and electromagnetic radiation is postulated. The agreement between experimental results and those predicted by this correspondence is quite good.