Examples of lamb

The signals shown in Figure 52 were computed by lamb in Test Mode (pol=0). The command to generate the Figure 18 signals is

lamb 150. 1.0 1 2. .0005 150. 1700. 1 100. .3 100. .3 0 0.

Not all of the parameters matter (density won't affect the result since it is test mode). There are many combinations of S-wave velocity and range that will work (see equation (44) for normalized time scale used here). You can generate the plots of Figure 52 to confirm correct operation of the code. This is done in Octave, execute the procedure traplt.m from within the Octave text window. Make sure you also have the functions bsegin.m and segyinfo.m, in the working directory as they are called by traplt.m . Also note that you will have to specify the axes limits to clip the signals as was done in Figure 52. After finishing execution, delete the second figure of the spectrum and then issue an axis command.

axis([0.4,1.4,-0.4,0.9]) % for the vertical motion
axis([0.4, 1.4, -1.2, 0.2]) % for the horizontal motion

As a second example of what lamb can do, we can generate 48 channel records for vertical and inline radial motion. The half-space medium has a mass density of 1700 $\frac{kg}{m^{3}}$ , a $V_{s}=250$ m/s and $V_{p}=433$ m/s. The command generating the synthetic seismograms is

lamb 1. 1.0 48 .5 .0005 250. 1700. 6 50. .7 10. .7 -1 0.

Figure 53 shows the resulting synthetics. Note that this is an elastic medium assumption. Actual soils may differ significantly from an elastic assumption. So, take it for what it is. The data have been rescaled to show waveforms. Each signal has been scaled by the L2 norm for that trace, thus removing the fading of amplitude with increasing offset.

Figure 53: Synthetic seismograms generated by lamb (see text for model)