Menu entry FK
External program, code mainly written by T. Kvaerna and Jan
Fyen.
Command to determine slowness and back-azimuth of a coherent
teleseismic phase. It transforms all traces within the current
time window in the main display into the frequency-wavenumber
domain. The resulting range in this square domain is displayed
in a separate window, the amplitudes (corresponding to wave energy)
are coded in colors. A good result is achieved when there is a
single, prominent maximum visible (yellow colors in the default
setup). This maximum denotes slowness and back-azimuth of the
investigated phase. Details of the FK algorithm can be found in
???.
After selecting the FK
entry a dialog box pops up. Its parameters are:
- lo frq, hi frq: frequency
window (in Hz) to which the FK computation should be restricted
to.
- max slow:
maximum slowness to compute (units either s/deg or s/km, see
below).
- resolution:
resolution of the resulting FK matrix, which is displayed in
the separate window. The computation time is strongly driven
by that parameter.
- num colors:
number of colors used in the display of the FK matrix.
- Unit: deg or
km used in input and output.
- OK: start
computation of FK matrix. Runs as independent background process,
i.e. the main window is fully operable. The results of the computation
have to be copied manually to the analysis
parameter box by calling the FK
menu entry again (then Get
Values).
- OK & Get Values:
start computation of FK matrix and copy the resulting slowness
and azimuth values to the analysis parameter box automatically.
The main window functions are disabled while computing.
- Get Values:
copy slowness and azimuth values of the last run of FK into the
analysis parameter box.
- Cancel: close
popup window and do not compute FK matrix.
After the computation of the FK matrix is finished a new window
pops up. This has the following menu entries:
- Plot: plot
FK matrix into window using linear amplitude scaling.
- Plot Log:
plot FK matrix into window using logarithmic amplitude scaling.
- Pow ++: increase
power of amplitude scaling (strongest peaks will be enhanced)
- Pow --: decrease
power of amplitude display (smaller peaks get more visible)
- Rad Grid:
toggle radial grid on and off.
- G - R: green
- red display of FK matrix
- B - R: blue
- red display of FK matrix
- B - W: black
- white display of FK matrix
- B - Y: blue
- yellow display of FK matrix (default)
- Quit: close
FK display window
This FK option
is an alternative to picking phases (manually or automatically)
and calling Plane Wave. However,
the suppositions for applications are the same:
- The epicentral distance must be much larger than the aperture
of the recording array.
- The dominating frequencies of the signal still allow coherency
- The station information of the recording array is found in
the station file. Required entries
are lat, lon, xrel, yrel
and array.
Technical remark:
The computation of the FK spectrum is done by an external program
located in the directory $SH_UTIL/fk_src.
It is mainly written by other authors (see above) and it is Fortran
code. Therefore it is not part of the SH/SHM program package.
It has to be downloaded separately and compiled if no executable
for your platform is available (see our ftp server
ftp://ftp.szgrf.bgr.de).
This page last modified 6-Jul-2000