Anisotropic wavefront

Drag the Thomsen parameters ε (epsilon) and δ (delta) — and a tilt angle for TTI — to deform the quasi-P wavefront away from the isotropic circle (dashed). Equal ε and δ give an ellipse; ε ≠ δ gives an anelliptic shape, with anellipticity η = (ε − δ) / (1 + 2δ) shown in the badge.

The wavefront is the exact group-velocity surface of the Thomsen weak-anisotropy qP phase velocity v(θ) = v₀ (1 + δ sin²θ cos²θ + ε sin⁴θ); ε sets the horizontal velocity and δ controls the near-vertical curvature.