“…Dynamic pressure P is given by the mean stress: where P is positive under compression. Computing the dynamic pressure as a solution of the continuity and momentum equations is especially crucial to obtain correct angles of forming faults that differ from a constant Roscoe angle (Buiter, ; Buiter et al, ; Kaus, ). Because our simulation represents a compressive state of stress, that is, σ 1 > σ 2 and we ignore dilation, that is, ψ =0, the four potential fracture surface orientations predicted by the Arthur angle (equation ) reduce to α 1 = 45° −( φ /4) and α 2 =−45° +( φ /4) (conjugate).…”