genwav

Program genwav is a helper program that generates a namelist file to be input to program waves. Run from an x-term, the program prompts the user for inputs which include descriptions of the simulated source (spectrum, moment tensor), and the simulated receiver array. Other documentation beyond what follows can be found in the wave man page. A description of the dialog follows:

1. Name of namelist file: This is limited to 40 characters, suggest using waves.d.
2. Name of dispersion curves file: The default from disper is earth.crv. This name is defined in the disper.d file input to program disper.
3. Near offset: This is the nearest geophone offset from the source in meters.
4. Number of receivers (nrec): This is the number of geophones deployed in the simulation.
5. Minimum group velocity expected: This is used to give a suggestion for the next parameter, tmax. It is more of a warning, since you must choose a sample interval and tmax that produce the exact same frequency spacing as was used in disper. The warning is an attempt to avoid a synthetic with FFT wrap-a-round which would result if the combination of maximum offset and record time would result in a wave running off the bottom of the record.
6. Sample rate (fsamin): This really is the sample interval in seconds.
7. Frequencies Hz (fmin, fmax): This defines the bandwidth of the simulated source. Should be the same as used in the disper run. Can be narrower than disper, but not broader (the curves file has only as many frequencies as were generated in disper.
8. Maximum mode: This sets the maximum mode number to be included. You can edit the namelist file later to change this, even doing specific mode simulations (as long as they were computed in disper).
9. Plot switch, ksw: This program selects the type of dispersion plots to be generated for dispersion. A value of zero gives velocity vs. frequency plots (phase and group velocity). A value of unity will produce wavenumber vs. frequency plots.
10. Plot format: A value of zero outputs Octave programs for dispersion plots (RECOMMENDED). The alternative is Maple. If you choose Maple, your mileage may vary depending on changes that may have occurred to Maple.
11. Component of motion (irvsel): The output options are 0=Vertical, 1=Radial component of motion in the output seismic traces. This is meant to simulate either vertical component or in-line radial component geophones.
12. Source depth: This is the depth of the simulated source below the assumed horizontal ground surface.
13. Diagonal elements of moment tensor: If you want to simulate a non-diagonal tensor, you can edit the namelist file, waves.d. A buried explosive source would use 1,1,1 here. A vertical impact source at the surface would use 0,0,1. This tensor controls the radiation pattern of the source, and combined with the source frequencies defines your source. The source wavelet (scalar source moment) is computed as a minimum phase wavelet, and is available in file m0.mat generated from the waves run. The wavelet at the source in file m0.mat is a text file, two columns, sample time and wavelet amplitude.

The example presented in this section will use the model of Figure 55 and the dispersion curves that were produced (earth.crv). The source will be a simulated vertical impact at the surface. The following is a log of the interactive run of genwav:

{genwav1}
  genwav
   enter name of namelist file (40 char)
   Example: waves.d
waves.d
   enter name of dispersion curve file
   (this is file from disper.f)
   Example: earth.crv
earth.crv
   enter near offset:  xnear 
1
   enter group interval:  delx 
1
   enter number of receivers:  nrec
48
   enter minimum group velocity expected
100
  RECOMMENDED minimum tmax=    0.9600
   enter: maximum trace time, tmax
2.0
   enter: sample interval (seconds), fsamin
.001
   enter frequencies: fmin, fmax 
1, 100
   enter maximum mode to include 
9
   enter ksw switch 0=c plot, 1=k plot
0
   enter type of plot format, mapmat
   0=octave (Matlab)  1=scilab
0
   enter Output option 0=Vertical  1=Radial 
0
   enter source depth
0
  enter (3) diagonal elements, moment tensor
0,0,1
  Padded Radix 2 tmax=    4.0960
  Number of points in signal= 4096
--------------------------------------------------
  .......Frequency interval=  0.24414061
  NOTE: Frequency Interval MUST MATCH DISPER OUTPUT
  WAVES will output signal length = 1.0/delf
  IF MISMATCHED: CHANGE sample rate in WAVES
                 or RERUN DISPER
--------------------------------------------------
  Number of frequencies=  409
  output in =====>waves.d

genwav1

After running genwav, we have the following waves.d namelist file.

  &waves
  ksw= 0, stepz=20,
  modes=1,2,3,4,5,6,7,8,9,
  fmin=    10.0000, fmax=  100.0000,
  fsamin=   0.00100,
  curve='earth.crv', 
  mapmat=0,
  matlb1='matc.m',   scilb1='matc.sci', 
  matlb2='matu.m',   scilb2='matu.sci', 
  irvsel=0,
  ofile='waves.tmp', /
  &source
  tm= 0.0, 0.0, 0.0,
     0.0, 0.0, 0.0,
     0.0, 0.0, 1.0, /
  sz=    0.00, sy=0.00, sx=0.00, /
  &recvr
  nrec=48,
  rz=48*0.0, 
  ry=48*0.0, 
rx=      1.000,     2.000,     3.000,     4.000,     5.000,
     6.000,     7.000,     8.000,     9.000,    10.000,
    11.000,    12.000,    13.000,    14.000,    15.000,
    16.000,    17.000,    18.000,    19.000,    20.000,
    21.000,    22.000,    23.000,    24.000,    25.000,
    26.000,    27.000,    28.000,    29.000,    30.000,
    31.000,    32.000,    33.000,    34.000,    35.000,
    36.000,    37.000,    38.000,    39.000,    40.000,
    41.000,    42.000,    43.000,    44.000,    45.000,
    46.000,    47.000,    48.000,
  /

Note that we have selected up to 9 modes, used a slightly narrower bandwidth than is available from the disper run, chosen a vertical impact source (matrix tm=) at the surface (sz=0.0), and a sample interval of .001 seconds. There are 48 geophones at the surface (rz=0.0) that extend in the x-axis direction along which the simulated Rayleigh wave will propagate. A vertical component geophone response is selected with irvsel=0. A listing file logging the run will be called waves.tmp. Plot programs will be in Octave format (mapmat=0). These plots will be in terms of velocity vs. frequency (ksw=0). There will be two dispersion plot programs, matu.m (group velocity) and matc.m (phase velocity, as from the disper run). A trace equalized plot of the synthetic seismogram is shown in Figure 58

Figure 58: Plot of vertical component motion, trace equalized to remove amplitude decay with offset. This permits viewing the waveform changes with offset. Compare this to the horizontal motion in Figure 60.

The group velocity plot is generated in a Octave session. Start Octave, and then in the Octave window, one types:

matu;

Figure 59 shows the group velocity plot. The corresponding phase velocity curves can be plotted by executing matc.m from within Octave. This will produce a plot similar to the plot in Figure 56, but limited to match the frequency range in the actual waves run that produced group velocities of Figure 59.

Figure 59: Group velocities are available by plotting matu.m from within Octave.