Description Usage Arguments Details References See Also

Calculate the ratio of principal *effective* stresses

1 | ```
StressRatio(mu, theta, thresh = NULL, in.deg = TRUE)
``` |

`mu` |
numeric; the static coefficient(s) of friction |

`theta` |
numeric; optional; the orientation(s) of the fault with respect to the principal compressive stress |

`thresh` |
numeric; an arbitrary clipping level for the stress ratio |

`in.deg` |
logical; is |

The ratio of principal effective stresses, *R*, is given by

*R=\frac{σ_1 - P}{σ_3 - P}=\frac{σ_1'}{σ_3'}=\frac{1 + μ/\tan{θ}}{1 - μ \tan{θ}}*

where *P* is the pore fluid pressure. This function calculates *R* as given above
and in Equation 4 from Sibson (1985).

Sibson (1995; Equation 4)

`Sibson.fric`

, and
`Stability`

, which calculates the minimum *R* for reactivation.

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