SH: Calculation of the direction of maximum horizontal stress...
In abarbour/stress: Tools for Working with Stresses and Focal-mechanism Inversions

Description Usage Arguments Value Author(s) References Examples

Calculation of the direction of maximum horizontal stress using a 3D relative stress tensor

1	SH(R, n1, n2 = NULL, n3 = NULL)

`R`	numeric; the principal stress ratio; defined as (S1 - S2)/(S1 - S3)
`n1`	numeric; the unit vector of the maximum principal stress, S1 (North,East,Up); if either `n2` or `n3` are `NULL` then this may be a three-column matrix
`n2`	numeric; unit vector of the intermediate principal stress, S2
`n3`	numeric; unit vector of the minimum principal stress, S3

numeric; the azimuth of SHmax (c.w. from North) in radians with full or partial knowledge of the tectonic stress tensor, Geophys. J. Int., 170, 1328-1335, doi: 10.1111/j.1365-246X.2007.03468.x

Equations 10 and 11 from Lund and Townend, (2007): Calculating horizontal stress orientations

# Dummy examples
Sf <- matrix(1:9, 3)
Sf[lower.tri(Sf)] = t(Sf)[lower.tri(Sf)]

S <- eigen(Sf)
principal_stresses <- S[['values']]
orientations <- S[['vectors']]

SH(0.5, orientations[,1], orientations[,2], orientations[,3])
SH(0.5, orientations)

Rseq <- seq(0, 1, length.out=21)
Azims <- sapply(Rseq, SH, n1=orientations)
plot(Rseq, Azims*180/pi, type='b')