Andersonian stress regimes and faulting
In an Andersonian idealization, one principal stress axis is vertical and two are horizontal.
Key knowledge
In an Andersonian idealization, one principal stress axis is vertical and two are horizontal. With compression-positiveσ₁≥σ₂≥σ₃, verticalσ₁ is associated with the normal-fault regime, verticalσ₃ with reverse/thrust faulting, and verticalσ₂ with strike-slip faulting. Plane orientation and resolved traction plus a calibrated failure law qualify the association; fault geometry alone does not determine all stress magnitudes.
Conditions and scope
- A locally horizontal surface with negligible tangential traction makes the vertical direction principal at that boundary; extending this orientation to depth is an explicit homogeneous/regional stress idealization, not a general theorem.
- Topography, heterogeneity, rotating/deformed or preexisting weak faults and oblique loading can violate the ideal geometry. Slip can reactivate a nonoptimal plane; no universal30°/60° dip or uniquely reconstructed present stress is claimed.
Sources · 1
References
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Evidence and review
Read actual free-surface argument, three vertical-principal-stress classifications and explicit preexisting-fault/rotation/local-heterogeneity/depth limitations. Retained boundary versus interior distinction and excluded universal dip angles, automatic convergence-regime inference and fixed friction coefficients.
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