Attenuation behaviour of tuffaceous sandstone and granite during microfracturing

Laboratory measurements of ultrasonic wave propagation in tuffaceous Sandst one (Kimachi, Japan) and granite (Iidate, Japan) were performed during incr easing fracturing of the samples. The fracturing was achieved by unconfined uniaxial compression up to and beyond the point of macrofracture of the sp ecimen using a constant low strain rate. The observed variation of wave vel ocity (up to 40 per cent) due to the development of micro- and macrofractur es in the rock is interpreted by rock models relating velocity changes to d amage and crack density. The calculated density of the newly formed cracks reaches higher values for the sandstone than for the granite.:Using the est imated crack densities, the attenuation behaviour is interpreted in terms o f different attenuation mechanisms; that is, friction and scattering. Rayle igh scattering as described by the model of Hudson (1981) may explain the a ttenuation qualitatively if the largest plausible crack dimensions are assu med in modelling.