bvax - BSU measure velocity dispersion of surface waves
bvax [ -h | infile | xmin | xmax | vmin | vmax | nvel | fmin | fmax | delf | bwd | iskip | ivscn ]
Basic Seismic Utilities (BSU) measures velocity as a function of frequency for waves recorded on a surface profile. Outputs include a history file, bvax.his, which records the velocity and standard deviation in velocity for each frequency. The user may limit the range of offsets for analysis. All offsets are filtered, and the limits are applied later in the VELSCAN of the filtered files. Not limiting the filter step permits trying different offset ranges on later runs when the filter sets are saved under the iskip option. NEW: The code has been changed since the bsu-3.0.2 version. The change includes internal sorting of the signals by offset before filtering. This results in an improvement in the offset selection step which originally assumed off end shooting. Now split spread and other acquisition geometries will have a correct offset limit result. The code is derived from the vertical seismic profile, bvas.F90 code. Fortran 90.
Options
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-h |
Online help giving details on command line arguments | ||
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infile |
Input file name | ||
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xmin |
Minimum geophone offset to include in the analysis zone (see DESCRIPTION above, NEW). | ||
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xmax |
Maximum geophone offset to include in the analysis zone. | ||
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vmin |
Minimum velocity for the scan. | ||
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vmax |
Maximum velocity for the scan. | ||
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nvel |
Number of velocities in the scan. | ||
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fmin |
Minimum frequency for the scan. | ||
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fmax |
Maximum frequency for the scan. | ||
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delf |
Frequency increment for the scan. See resolution comment for bwd. | ||
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bwd |
Bandwidth of the filters. Do not try to exceed the resolution implied by the recording aperture. Thus, bwd should not be less than 1/(npts*fsamin), where npts is the number of samples in the trace, fsamin is the sample interval. | ||
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iskip |
(-1=NO), do not skip filter step, and to save disk space, delete each bvaxyyyy.seg when done. |
0=NO, do not skip filter, data
sets bvaxyyyy.seg do not
exist in directory.
1=YES, skip filter step (assumes previously run and data
sets saved as bvaxyyyy.seg)
|
ivscn |
0=NO, do not save the velocity scan waveform panels |
1=YES, do save the velocity
scan waveform panels (CAUTION:
this could be a very big file)
NOTE:
If invoked with no options, will prompt user for input
parameters.
EXAMPLE:
bvax wave.seg 0. 120.00 100. 2000. 40 6. 100. 2. 2. 0 0
Input file wave.seg is processed for the offset interval from 0. to 120. meters. The minumum velocity scanned will be 100 m/s, the maximum velocity will be 2000 m/s. The velocity scan will be made in 40 steps. The minimum frequency scanned will be 6 Hz, the maximum frequency scanned will be 100 hz. The frequencies will be scanned every 2 Hz (thus center frequencies scanned are 6, 8, 10, ... to 100 Hz). The bandwidth of each filter is 2.0 hz. Don’t skip filtering the data (first time run) and don’t write a velscn file (that would provide too many pannels with a 40 velocity step scan).
bvax.ps
Postscript plot of auto picked dispersion likely to be fundamental mode. Also shown is a semblance plot.
bvaxqc.ps
Postscript plot of auto picked dispersion as Quality Control images (relative corrected time picks from cross correlation against alignment time. Error is measured by point deviations from horizontal fit line.
bvax.his
Text file of frequency (hz), phase velocity (m/s), standard deviation of velocity.
semblance.dat
Data file with (frequency, velocity, semblance) triplets. This file is formatted for input into the Gnuplot generated scripts.
CLRplot.gp
Gnuplot script plots semblance image for (frequency,phase velocity) space. Colors correspond to semblance value. This script is also run during the run of bvax.F90, creating the image clrplot.png.
CNTplot.gp
Gnuplot script plots semblance image for (frequency,phase velocity) space. Image is a contour plot with contours that correspond to semblance value. This script is also run during the run of bvax.F90, creating the contour plot image cntplot.png.
GRYplot.gp
Gnuplot script provides a gray scale image. Script not run by bvax.F90, that would be up to the user. Type gnuplot to open a gnuplot shell. Then ’load GRYplot.gp’ will start an interactive plot.
MSHplot.gp
Gnuplot script provides a mesh type image. Script not run by bvax.F90, that would be up to the user. Type gnuplot to open a gnuplot shell. Then ’load MSHplot.gp’ will start an interactive plot.
bvaxyyyy.seg
If iskip=0, saves filtered, trace equalized data (all elevations). The frequency is encoded in the file name as the yyyy suffix.
vscnyyyy.seg
If ivscn=1, saves filtered velocity scan panels. CAUTION: This can produce an VERY large file. HIGHLY RECOMMEND that nvel=5 or some small number if you do this. The name of the file has the frequency encoded with the yyyy suffix.
bvaxyyyy.lst
Listing file for bvax. The characters, yyyy, will be the first 4 char of the input file name.
standard output
list of frequency, velocity, std. dev., semblance, and number of steps in golden section search.
bhelp(1), bvas(1)
No known bugs. In cases of noisy data, or a thin zone of analysis, or a poor choice of scan limits, the semblance may not peak. In that case, the code skips that frequency and moves on. It is also possible to have multiple peaks if higher modes are present or if aliasing occurs. It is the responsibility of the user to avoid spatial aliasing and QC the listing file, bvaxyyyy.lst.
Copyright © 2021 by Paul Michaels
This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
P. Michaels, PE. <[email protected]>