Principle of Superposition

The principle of superposition states that in a sequence of undisturbed sedimentary layers, the oldest layers are on the bottom and the youngest layers are on the top.

This principle was formulated by Nicolas Steno in the 17th century.

Thrust faults can alter the understanding of the principle of superposition because they occur parallel to bedding and can be hard to detect. They can create situations where older layers overly younger layers. Scientists of Nicolas Steno's time were unaware of thrust faults.

Anderson's Theory of Faulting

Assuming that there is no shear stress at the Earth's surface (shear stress cannot occur in fluids), one of the principal stress components must be vertical and thus the other two must be horizontal.

σv = σ1 normal fault

σv = σ2 reverse fault

σv = σ3 strike-slip fault

Anderson's Theory of Faulting

Normal, Reverse, and Strike-Slip Faults