Editing the namelist file, disper.d

You can edit the disper.d file to make changes, should you wish to change something, or run a motion-stress vector plot. The showmdl listing augments the contents of the disper.d file with the layer control points at the bottom of the listing. The shear modulus (mu) and Lame's constant (lame) are computed from your velocities and densities.

Note that there are some additional parameters set to zero, pvlcty and pfreq. Also, parameter zend is set to 100 meters maximum depth, arbitrarily. If the first two are set to zero, then a dispersion curve is calculated over the specified frequency range. You can compute motion-stress vectors at a single frequency by assigning the correct values to these two parameters. When the namelist file is input to disper, the computed dispersion curve is captured in a listing, disper.tmp, as well as in a phase velocity Octave program, output as phase.m by default (unless you change it by editing disper.d).

You compute a dispersion curve by executing the following command at the command line:


disper disper.d


Examination of the output listing file, disper.tmp at a frequency of 40.0390600 Hz will show the following:


40.0390600 | 99.2208411 226.1749195 361.9392410


On this line of output, we see that there are 3 modes possible at this frequency. The phase velocity of the fundamental mode is 99.2208411 $m/s$. The highest mode has a phase velocity of 361.9392410 $m/s$.

We copy disper.d to disper1.d and edit the copied file to compute the fundamental mode motion-stress vectors. The edited file might look like this:


{disper1}
   &disper 
  nlay=    3,
rho= 0.1600E+04, 0.1600E+04, 0.1700E+04,
mu= 0.1600E+08, 0.1600E+08, 0.2720E+09,
lame= 0.9920E+09, 0.9920E+09, 0.6256E+10,
zi= 0.0000E+00, 0.2000E+01, 0.2001E+01,
  deltz=   0.0500,
  modemx=9,
  nfreq=610, flo=  0.1000000E+01, delf= 0.24414061E+00,   jsmax=300, ksw=0,
   pvlcty=99.2208411  , pfreq=40.0390600, zend=5.,
  ofile='disper.tmp',
  octav1='phase.m', octav2='mat2.m',
  curve='earth.crv', /
disper1


Note that the line beginning with pvlcy has been edited, and the deltz value has been decreased to make a better sampled motion-stress vector plot. With these changes, we re-run disper with this file, and the Octave program file, mat2.m is created instead of phase.m. We can execute that program by starting a Octave session and executing mat2.m . From within Octave, we type:


mat2;


Figure 57 shows the plot generated by Octave and the mat2.m program. There have been some additional annotations drafted to show key points (vanishing stress boundary condition at the surface, top of half space, and identification of the vertical and horizontal components of motion).

Figure 57: Motion-stress vectors for simple layer over a half space model of Figure 55. A) Displacement vectors, B) Stress vectors. Horizontal motion is R1, vertical motion is R2. Horizontal stress is R3, vertical stress is R4.
\includegraphics[scale=0.7]{FigureY}