Triplications and cusp edges can occur in homogeneous transverse isotropy (TI) provided the strength of anisotropy exceeds a critical value. The critical strength of anisotropy is 9.50% for axial triplication, 9.71% for basal triplication, 8.86% for oblique triplication, and 9.72% for double triplication. No TI with strength less than the critical can display triplications. On the other hand, high values of the strength of anisotropy do not guarantee the existence of triplications. Hence, observations of triplications on the wave surface cannot serve as a unique criterion defining strong TI.

• Received 26 March 2003

DOI:https://doi.org/10.1103/PhysRevB.68.054107