Attenuation of Stress Waves in Cedar City Quartz Diorite

The attenuation of a finite amplitude stress wave in a quartz diorite from Cedar City, Utah, was estimated from static compression tests under confining pressure. Measurements were made at pressures up to 7,500 psi and deviatoric stresses up to 10,000 psi. Energy dissipated was calculated from stress-strain curves for complete loading-unloading cycles. Total relative attenuation, defined as the ratio of the energy lost to the maximum energy stored in the sample, was found to be approximately independent of the level of deviatoric stress. Relative attenuation was about 0.5 at 7,200 psi. Attenuation in Cedar City quartz diorite is about five times greater than the value for a more typical compact granite, apparently because of the loose structure resulting from past alteration. A significant proportion of the energy dissipated arises from work done compacting the rock under pressure, again a characteristic arising from the losse structure of the quartz diorite and unlike typical unaltered igneous rocks. (Author)