Internal friction in rocks

This paper intends to show that the low-amplitude effects, in particular the attenuation proportional to the frequency from very low frequencies up to the kilohertz range, are connected with the motion of dislocations in cracks. The measurements have been made of the resonant frequencies and the internal friction of spherical rock speciments, including Solenhofen limestone, Indiana limestone, Westerley Granite, Friedensville sphalerite, galena, magnetite, and olivine of small grain sizes. The different types of stresses are thus easily determined through the various modes of motion. On the basis of dislocation motion in cracks, it is shown that the ratio of the radial Q to the torsional Q is about 0.8 and is nearly independent of the crystal structure. This result is in agreement with the measurements, which vary from about 0.6 to 0.9. From longitudinal and torsional measurements of cylinders, the torsional Q’s are nearly twice those for the longitudinal mode. The model used also agrees with the variation of velocity and Q with the external pressure.