(a) Phase tensor ellipses at all periods used in the inversion at the locations shown by green dots in Fig. 1, ellipse colour showing Φ_2. (b) Calculated phase tensors from the preferred model. Contours show the rms 0.5*√(Δxx²+ Δxy²+ Δyx²+ Δyy²) of the tensor misfit (Δ) defined as Δ = I—Φ_cal *Φ⁻¹_obs, where I is the identity matrix and Φ_obs and Φ_cal are the observed and calculated phase tensors.