(An)elastic softening from static grain boundaries and possible effects on seismic wave propagation

It is argued that low-frequency wave propagation shows, in most cases, very little dependence on the atomistic properties of grain boundaries if the thickness of the grain boundary is atomistically thin while the grain size is in the mm region. Large effects do exist for specific textures (e.g. the brick wall texture). The essential ingredient for the assessment of an-elastic and non-linear elastic features of seismic wave propagation does not primarily depend on the structural properties of immobile, dry grain boundaries but on the way the grain boundary properties can be related to those of macroscopic mineral assemblies. Specific results for coated sphere textures are derived using Hashin-Shtrikman theory. An-elastic seismic features are more likely to be related to the mobility of boundaries and dislocations which can be attached to the grain boundaries, or bulk-related defect structures, rather than the intrinsic materials properties of the grain boundaries.