Fig. 1.

Wave propagating with two polarization directions in a TI material. (a) A “slow” shear wave is produced by harmonic shear displacement in the slow polarization direction, ${\mathbf{m}}_{\mathbf{s}}$. (b) A “fast” shear wave arises from harmonic shear displacement in the fast polarization direction, ${\mathbf{m}}_{\mathbf{f}}$. The wavelength of a fast shear wave is typically longer than that of a slow shear wave. Reproduced from Ref. [16].