Slow wave processes in compressed rock samples and alkali halide crystals

Spatiotemporal distributions of local components of the distortion tensor of quasi plastic material - rocks have been studied under active compressive straining conditions using double exposure speckle photography techniques. The strain localization patterns are presented and the features of macroscopic strain inhomogeneity are considered for inelastic behavior of the material. Results obtained for the slow wave processes in deformed rocks are compared to analogous data available for ionic crystals. The deformation is found to occur by different mechanisms in the compressive rock samples and alkali halide crystals investigated, i.e. silvinite, marble, sandstone, NaCl, KCl and LiF. The development of localized plastic deformation has an autowave character. These results confirm the common nature of wave processes in mono- and polycrystalline metals and alloys. The autowaves originating in the course of the samples compressing have propagation rates ~10-5…10-4 m/s, which are close to the respective values obtained for slow S-waves, which propagate in the earth's crust after earthquakes or mine shocks (0.3…3.0 k per year). The discovery of slow wave processes in plastically deformed rocks and ionic crystals related to processes of self organization in deformed media must be taken into account in interpreting geological phenomena such as the formation of faults, fractures, folds.