= Solution
Interpret the vertical, apparently unoffset fractures as opening <geological joints>. Their normals are east–west, so the least <principal stress> $\sigma_3$ must be east–west and sufficiently tensile in <effective stress>. The other two <principal stresses> lie within the vertical north–south <geological joint> plane; their ordering cannot be recovered from this fracture orientation alone.
One example, with compression positive and coordinates east, north, up, is
$$
\boldsymbol\sigma'=\begin{pmatrix}-3&0&0\\0&5&0\\0&0&10\end{pmatrix}\ \mathrm{MPa}.
$$
Here $\sigma_1$ is vertical, $\sigma_2$ north–south, and $\sigma_3=-3\ \mathrm{MPa}$ east–west. The <geological joint> opens east–west when its <tensile strength> is $3\ \mathrm{MPa}$. An isotropic <pore pressure> can make the east–west <effective stress> tensile even while the total <normal stress> remains compressive. Draw opening arrows pointing away from the vertical fracture, rather than sliding arrows along it.
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