Elastic behaviour of rocks at low frequencies
M. J. Usher
Journal name: Geophysical Prospecting
Issue: Vol 10, No 2, June 1962 pp. 119 - 127
Info: Article, PDF ( 507.03Kb )
An apparatus is described for the measurement of Young's modulus, E, and the energy loss per cycle, ΔW/W, of small beam-shaped rock samples, over the frequency range 2 to 40 c/s. Results are given for seven sedimentary and two igneous types of rock. An increase of between 1 % and 3 % in E, and of up to 100 % in ΔW/W, occurred over this range. Experiments on rocks containing moisture showed a decrease in the magnitude of E (at 2 c/s), an increased frequency variation of E, and a greater and almost linear increase of ΔW/W with frequency. The effect of oil was similar except that the magnitude of E at 2 c/s was unaffected. It is suggested that the moisture and oil results are due to viscous movements of fluid through the pores in the rock, and that the changes in E and ΔW/W with frequency, in dry rocks, are due to a small viscous mechanism operative at low frequencies.