                      VMONTECARLO USAGE

Monte Carlo approach to assess the uncertainty of wide-angle layered models


1 - Copy v.in, r.in and tx.in files for the preferred model into
    a working directory fot vmontecarlo. For increased performance,
    it is recommended to build a tx.in file with only the arrival
    times that will effectively be used.

2 - Set flags on the nodes of interest
    This can be done with program vnodes. See vnodes -h
    Main output of vnodes is v.in.orig

3 - Copy v.in to v.in.neg and v.in.pos
    On v.in.neg and v.in.pos, and for each node of interest,
    change the depth of velocity value to the maximum allowable
    deviation from the preferred value. If a layer pinches out,
    the depth nodes of the lower layer that are coincident with
    the upper layer's have their flags set to 3 in v.in.neg

4 - Edit the values of vmontecarlo.in and thresholds.in
    If these files do not exist, VMONTCARLO will create them
    with default values.

    vmontecarlo.in
    &mntcrl
     xvp=  (location of the 1D velocity-depth profiles. Up to 16)
     nmodls= (number of simulations)
     idist= (type of distribution. Gaussian =0. Triangular =1. Use Gaussian)
     wa= (scoring function shape factor psi. Default =1.  Weight A for other
          types of scoring functions)
     wb= (weight B for other scoring functions)

    &grads (FROM VERSION 2.35 ONWARD - PREVIOUS VERSION IGNORE THIS NAMELIST)
     hgrad= (maximum lateral gradient in km/s /km )
     vgrad= (maximum vertical gradient in km/s /km )

    thresholds.in
    &thresh
      tpcray= (fraction of the original number of traced rays that a new model
               must trace to be considered good. Default 0.95)
      tpcrms= (how much worse can the RMS of a new model be? Default 1.1)
      tpcchi= (how much worse can the Chi-square of a new model be? Default 1.1)

5 - Run Vmontecarlo. For stability purposes, it is not recommended to
    run it in internal mode (vmontecarlo -i).

6 - Run vmontecarlo -h to see all the different options.
    The metropolis-Hastings approach (flag --mk) automatically
    adapts the variance to increase the convergence rate.
    If this is not desired, it can be turned off with flag
    --non-adaptive

7 - Run Vthresplot to create the final uncertainty grids.
    From v3.00 onwards, the preferred output format of
    VMONTECARLO is a binary file. VTHRESPLOT can convert
    between the output formats, or export individual models.

8 - Make plots. Interpret results.
    Plotting scripts depend extensively of GMT4 programs.
    If you use GMT5, some changes are required.
    If GMT is not available, Vmontecarlo outputs are plaintext
    and can be processed with other tools.
    The most useful script is probably plot_uncertainty.sh

Notes: Every program can be invoked with the -h argument to
       output a small help text describing running options.

       The listing of each program has a detailed description
       of the inputs, outputs and logical units used.
       A changelog and program description are also present.


Source available at: http://afonsoloureiro.net/vmontecarlo/     

How to reference VMONTECARLO:

A. Loureiro, A. Afilhado, L. Matias, M. Moulin and D. Aslanian. Monte Carlo approach to assess the uncertainty of wide-angle layered models: Application to the Santos Basin, Brazil. Tectonophysics, 2016. doi: 10.1016/j.tecto.2016.05.040.
