BVAX

Run BVAX for surface wave dispersion measurement. A number of image files are created, and the file bvax.his is available for use in the inversion program invR1.m (run in octave). To run invR1.m in octave, execute build_disper_oct script to build an extension to octave. Edit the bvax.his file to remove any measurements that are zero or bogus velocities. NOTE: BVAX determines PHASE velocities in the time domain.

  bvax infile xmin xmax vmin vmax nvel . . .
           fmin fmax delf bwd iskp ivscn
  
 infile  =input file name 
 xmin    =minimum offset (float) 
 xmax    =maximum offset (float) 
 vmin    =minimum velocity 
 vmax    =maximum velocity 
 nvel    =number of velocity increments
 fmin    =minimum frequency Hz
 fmax    =maximum frequency Hz 
 delf    =frequency increment Hz 
 bwd     =filter bandwidth Hz 
 iskp    =skip filtering (if files already exist)
           1=YES  0=NO (-1=NO and delete when done)
 ivscn   =output velocity scan data sets 
           1=YES  0=NO
           
 EXAMPLE: bvax c008.seg 1.0 100. 100. 500. 200 10. 50. 1. 1. -1 0

Figure 15: BVAX: Phase velocity semblance display file, clrplot.png. For details on semblance, see Sheriff (1991). Semblance provides a measure of the degree to which the data were aligned at a trial velocity.
\includegraphics[scale=0.5]{Figure16.pdf}
Figure 16: BVAX: Phase velocity semblance display file, bvax.ps
\includegraphics[scale=0.5]{Figure17.pdf}

There are some useful data at the frequencies above and below the 20-30 Hz range. The file, bvax.his should be edited to remove questionable data with a lot of scatter (perhaps due to higher modes), or in some cases where zero velocity is returned due to a failure to find a phase velocity. That happens when the range of velocities scanned is too limited, or when there is no signal. Once edited, an inversion in Octave can be done with program invR1.m.