Pic src: Earth structure – An introduction to structural geology and tectonics
The four basic patterns arising from fold superposition. The analysis assumes
that F2 shear folds (a2 is the relative shear direction and b2 is the hinge line) are superimposed on a preexisting F1 fold of variable orientation. Shear folds are modeled by moving a deck of cards. The shaded surface is the S1 axial surface.