TauP VelocityMerge

TauP VelocityMerge overlays a partial velocity model over the given base velocity model. This makes is easy to overlay a new crust and upper mantle structure on an existing global model.

One common source of errors with cusom models is users forgetting that TauP requires a full earth model because the radius of the earth is given by the deepest sample in the velocity model. A model file that shows depths only down to 30 kilometers may look like a model of the crust of the earth, but TauP will assume your planet has a radius of only 30 kilometers, so something more like asteroid seismology. In order to calculate even just crustal phases, you will need layers between the crust and the center of the earth.

For example if dumbcrust.nd contains:

0.0 3 2 4
5.0 3.1 2.1 4
21.0 3.2 2.2 4
mantle
21.0 8.1 4.4 3.3
30.0 8.1 4.4 3.3

then we need to paste a model like prem beneath it. So running taup velmerge --mod prem --ndmerge dumbcrust.nd -o prem_dumbcrust.nd

would create a velocity model called prem_dumbcrust that contained the layers from our model and then prem below to give a model radius of 6371 kilometers:

0.0 3.0 2.0 4.0
5.0 3.1 2.1 4.0
21.0 3.2 2.2 4.0
mantle
21.0 8.1 4.4 3.3
30.0 8.1 4.4 3.3
30.0 8.107228461538462 4.488757435897436 3.3801497435897434
40.0 8.10119 4.48486 3.37906
60.0 8.08907 4.47715 3.37688
...
6271.0 11.26064 3.6667 13.0863
6371.0 11.2622 3.6678 13.08848

If the discontinuity at 30 km depth is not desired, the –smbot argument will create a smooth transition from the bottom of the new model to the first depth sample in the base model. Care should be taken with named discontinuities if they are different in the merged model by making sure there is enough depth in the merge to cover the named in both models. The merge model does not have to start at the surface, it can be just a range of depths.

The usage is:

Usage: taup velmerge [--debug] [--help] [--smoothbot] [--smoothtop] [--verbose]
                     [--elev=<elevation>] [-o=<outFile>]
                     [--prop=<toolPropsFilename>] ([--mod=<modelName>] |
                     --nd=<nDModelFilename> | --tvel=<tvelModelFilename>)
                     (--modmerge=<modelName> | --ndmerge=<nDModelFilename> |
                     --tvelmerge=<tvelModelFilename>)
Merge part of one model into another.

Options:

      --debug              enable debugging output
      --elev=<elevation>   increase topmost layer by elevation (meters)
      --help               display this help message
  -o, --output=<outFile>   output to file, default is stdout.
      --prop=<toolPropsFilename>
                           load defaults from properties file
      --smoothbot          smooth merge at bottom
      --smoothtop          smooth merge at top
      --verbose            enable verbose output
Base Velocity Model
      --mod, --model=<modelName>
                           use velocity model "modelname" for calculations,
                             format is guessed. Default is iasp91.
      --nd=<nDModelFilename>
                           "named discontinuities" velocity file
      --tvel=<tvelModelFilename>
                           ".tvel" velocity file, ala ttimes
Merge Velocity Model
      --modmerge=<modelName>
                           velocity file to merge, format is guessed
      --ndmerge=<nDModelFilename>
                           "named discontinuities" velocity file to merge
      --tvelmerge=<tvelModelFilename>
                           ".tvel" velocity file to merge, ala ttimes