Puzzles and the maximum-effective-moment (MEM) criterion in structural geology

► Obtuse angles in the σ1-direction are characteristic of conjugate ductile shear zones. ► Most geologists regard them as result of progressive deformation. ► The MEM criterion, however, states that the angles (usually ∼110°) are original features. ► The 110° seems to be a material-invariant for the scale-range of 10−7-106 m.