Influence of Structure and Cracks Distribution on P-wave Velocity Anisotropy in Rocks - Laboratory and Field Study

Physical properties of rocks are often investigated by laboratory methods. The extrapolation of the laboratory results anisotropy of P-wave propagation to larger rock units requires comparison with direct field measurements. The purpose of this contribution is this comparison between laboratory and field measured anisotropy of P-wave. Field measurements and rock sampling for laboratory tests carried out on the outcrop of peridotite massif in the Ivrea zone - north-western Italy. The direct surface seismic measurement of elastic waves velocity was realized by means of shallow seismic refraction method on base approximately 10m. Laboratory tests were realized on spherical samples with diameter 50 mm by using ultrasound velocity measurement in 132 directions under confining stress from atmospheric level up to 150 MPa. The common laboratory and field research can reveal reasons of anisotropy at different scales. Scaling factor is effected dominantly by different sampling size. Laboratory samples contain only microcraks, which represents nearly continuum with regard to ultrasound wave length (11 mm). Rock massif, however, contains beside mickrocraks also cracks with comparable size of applied seismic wave length (10 m).