Last modified 14 years ago Last modified on 01/23/2009 11:37:26 AM

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.

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

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