## Rotationally invariant viscoelastic medium
with a non-symmetric stiffness matrix

**Ludek Klimes**
### Summary

The stiffness matrix of a viscoelastic medium is symmetric
in the low-frequency and high-frequency limits,
but not for finite frequencies.
We thus consider a non-symmetric stiffness matrix in this paper.
We determine the general form of a rotationally invariant
non-symmetric stiffness matrix of a viscoelastic medium.
It is described by three additional complex-valued parameters
in comparison with a rotationally invariant symmetric
stiffness matrix of a transversely isotropic (uniaxial)
viscoelastic medium with a symmetric stiffness matrix.
As a consequence, we find that the stiffness matrix
of an isotropic viscoelastic medium is always symmetric.

### Keywords

Viscoelastic media, stiffness tensor, elastic moduli,
transverse isotropy, symmetry axis.

*Stud. geophys. geod.*, **66** (2022), in press.