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.dgenwav1
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
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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.