In all media in which the elastic stiffness tensor and density vary in space, an implicit, frequency-dependent anisotropy is present, even if the medium is locally isotropic. This predicts a non-linear, frequency-dependent polarization of body waves, and explains shear-wave splitting in heterogeneous media. Examples are presented for compressional and shear waves in a medium in which the elasti...

Numerical simulations are performed to study the propagation of elastic waves in a 2-D random heterogeneous medium such as concrete. To reduce spurious numerical artefacts to a negligible level, a fourth-order time-domain numerical scheme and an immersed interface method are used together. Effective properties of the equivalent homogeneous medium are extracted and compared to the predictions of...

We study the process of formation of spiral waves in a heterogeneous excitable medium under external stimulation, using numerical and analytical methods. We show that in an excitable medium with several heterogeneities with respect to refractory period, fast rotating spiral waves can be generated. These fast spirals are formed as a result of a phenomenon of period decrease, which is the generat...