 Solution

Use compression-positive principal stresses, ${\sigma }_1\ge {\sigma }_2\ge {\sigma }_3$. For the intended thrust fault regime during approximately north–south tectonic shortening, the likely orientations areA locally horizontal traction-free surface motivates taking one principal direction as vertical, while the strong north–south compression selects the maximum horizontal principal stress. The expected fault strike is then approximately east–west.

This ordering assumes the two horizontal compressions exceed the vertical principal stress. North–south shortening by itself does not establish the magnitudes of all three: if the vertical principal stress were intermediate, strike-slip faulting would instead be possible. The answer above is the simple compressional end member used in the following parts.