grotseis {RSEIS}

Get seismic rotation matrix

Description

Set up a rotation matrix for a seismic trace. Rotation matrix is 3D, although this rotation only creates a rotation for conversion to radial-transverse orientation.

Usage

grotseis(ang, flip = FALSE)

Arguments

ang

Angle to rotate horizontal components, degrees

flip

Logical, TRUE=flip the vertical axis, default=FALSE

Details

Returns a 3 by 3 matrix used for rotationg a 3-component seismic record, usually stored as an N by 3 matrix. Only the N-E components are rotated, North component is assumed to be in position 2 and the east compnent is assumed to be in position 3. The vertical component can be flipped.

If Back-Azimuth is used, radial is directed towards the source. If azimuth is used, radial is directed away from the source.

Value

3 by 3 rotation matrix.

Note

Positive radial is away from the source (direction of wave propagation). Positive transverse is to the right when facing the direction of wave propagation.

Author(s)

Jonathan M. Lees<[e-mail]>

See Also

rdistaz

Examples

####  simple case:


vecs  <- rbind(c(0,0,1), c(0,1,0))
rbaz <- grotseis(21.76, flip=FALSE) 
bvec  <- vecs %*%  rbaz

plot(c(-2,2) , c(-2,2) , asp=1, xaxs="r"  , yaxs="r" , type='n' )

  arrows(0, 0, 0+bvec[,2], 0+bvec[,3],
     col=c("red", "blue"), length=.08)
     
  arrows(0, 0, vecs[,2], vecs[,3],
     col=c("red", "blue"), length=.08, lty=2)

text(0+bvec[1,2], 0+bvec[1,3], labels='radial', pos=3)
text(0+bvec[2,2], 0+bvec[2,3], labels='transverse', pos=4)

text(0+vecs[1,2], 0+vecs[1,3], labels='North', pos=3)
text(0+vecs[2,2], 0+vecs[2,3], labels='East', pos=4)

 
####  realistic case:
STAXY<-list()

STAXY$'x'<-c(-2.9162198461534,-2.49599248511068,
-2.85909405321704,-1.96135073099434,
-6.50413342506259,2.64026676599765,
-3.95701139503518,-2.84082134537436,
-0.0457817300378462,-2.74214190991955)
STAXY$'y'<-c(-7.83435541676815,-4.46180337254565,
-6.46036190991833,-5.01212763828746,
-2.56091416028758,
5.31173503708142,2.10545324503380,-0.87490923667824,
-0.172422188354707,-1.52055218789877)

STAXY$'lat'<-c(14.685621984127,14.7159182222222,
14.6979647030651,14.710975070028,
14.7329873333333,14.8037143111518
,14.7749104943935,14.7481391460905,
14.7544511215933,14.7423394025875)

STAXY$'lon'<-c(268.420918730159,268.424817925926,
268.421447725096,268.429783940243,268.387586722222,
268.472531954619,268.41123843527,268.421611351166,
268.447574716981,268.422528671994)

STAXY$'z'<-c(0.92522857142857,1.48225333333333,
1.14740517241379,1.4423781512605,1.51148,
2.53268681318681,2.70014678899083,2.04094444444444,
2.90827547169811,2.31817123287671)

STAXY$'cen'<-c(14.756,-91.552)

STAXY$name<-c('OBS','CAR','MAR','CAS','MTB','STA','STE','MOT','SUM','DOM')
sguitoXY<-list()
sguitoXY$'x'<-c(-1.78551922571555)
sguitoXY$'y'<-c(-1.80850340813817)
sguitoXY$'lat'<-c(14.7397535236)
sguitoXY$'lon'<-c(268.4314147874)
sguitoXY$'z'<-c(2.501)

DAZ <- rdistaz( sguitoXY$lat, sguitoXY$lon ,       STAXY$lat, STAXY$lon)

STAXY$az <- DAZ$baz

####  plotting
plot(STAXY$x, STAXY$y, asp=1, xaxs="r"  , yaxs="r" )
text(STAXY$x, STAXY$y,STAXY$name, pos=3)
points(0,0, pch=3)
points(sguitoXY$x,sguitoXY$y , pch=8)
segments(sguitoXY$x, sguitoXY$y, STAXY$x, STAXY$y, col="green", lty=2)

#### be aware of the convention used: (V-N-E) or (V-E-N)
### here first vector is east, second vector is north
###       if you use the V-N-E convention
vecs  <- rbind( c(0,1,0), c(0,0,1))

for( i in 1:length(STAXY$x))
  {
rbaz <- grotseis(STAXY$az[i], flip=FALSE)
bvec  <- vecs %*%  rbaz
##############   red is north, blue east
########         red is radial positive away or toward  source, blue is transverse
##########       blue is positive rotated to the right of red
##
arrows(STAXY$x[i],STAXY$y[i], STAXY$x[i]+bvec[,2], STAXY$y[i]+bvec[,3],
col=c("red", "blue"), length=.08)

}