Fig. 14

a Estimation of the absolute value of shear comparing the phases from the quadratic equation and the phase tensor. \({\chi }^{2}\) objective functions for the estimation of twist: b assuming \({Z}_{+}\) as \({Z}_{xy}\) and c assuming \({Z}_{+}\) as \({Z}_{yx}\). The black lines in b and c represent the functions for positive shear and the red lines for negative value. The lowest \({\chi }^{2}\) corresponds to the assumption of \({Z}_{+}\) as \({Z}_{xy}\) and a negative shear