# Rotation of maximum principal stress near wellbore (Zoback \ Day-Lewis)

## Input(s)

A: Constant a Value (dimensionless)

\(\Delta\): Fault Orientation (degrees)

q: Ratio of Pore Pressure to Differential Stress (dimensionless)

## Output(s)

\(\gamma\): Stress Rotation (radian)

## Formula(s)

\[
\gamma=0.5 * \operatorname{atan}\left(\mathrm{A} * \mathrm{q} * \frac{\sin (2 * \Delta)}{1+\mathrm{A} * \mathrm{q} * \cos (2 * \Delta)}\right)
\]

## Reference(s)

Mark D. Zoback, Reservoir Geomechanics, Cambridge University Press, UK, Page: 393.