Thread: flat-earth angles, distances, and src/rec locations

Started: 2011-07-08 20:24:32
Last activity: 2011-07-13 04:50:12
Topics: SAC Help
Dear sac-help:

I am wanting to compare synthetic seismograms computed using a
flat-earth model using two different techniques. It seems like it
would be easiest to "turn off" the sphericity/ellipticity of the
Earth, and then input the source and station locations in, say, km.
And then the azimuth and back-azimuth angles would differ by exactly
180 degrees. I do not see a sac header that might do this -- is there
a simple solution? Alternatively, it seems I could set LCALDA = false,
and then manually enter at least some information, but it would be
safer to have sac to the computations based on input source and
station locations.

Thanks,
Carl

---------------------------------------------------------------
Carl Tape
Assistant Professor
Geophysical Institute
University of Alaska Fairbanks
Phone: 907-474-5456
Email: carltape<at>gi.alaska.edu
Web: http://www.giseis.alaska.edu/input/carl/
---------------------------------------------------------------

  • Philip Crotwell
    2011-07-11 15:24:46
    The easiest way might be to put the station and the event on the
    equator, then az and baz are 180 off each other and the ellipticity
    doesn't impact the distance.

    Philip

    On Fri, Jul 8, 2011 at 5:24 PM, Carl Tape <carltape<at>gi.alaska.edu> wrote:
    Dear sac-help:

    I am wanting to compare synthetic seismograms computed using a
    flat-earth model using two different techniques. It seems like it
    would be easiest to "turn off" the sphericity/ellipticity of the
    Earth, and then input the source and station locations in, say, km.
    And then the azimuth and back-azimuth angles would differ by exactly
    180 degrees. I do not see a sac header that might do this -- is there
    a simple solution? Alternatively, it seems I could set LCALDA = false,
    and then manually enter at least some information, but it would be
    safer to have sac to the computations based on input source and
    station locations.

    Thanks,
    Carl

    ---------------------------------------------------------------
    Carl Tape
    Assistant Professor
    Geophysical Institute
    University of Alaska Fairbanks
    Phone: 907-474-5456
    Email: carltape<at>gi.alaska.edu
    Web: http://www.giseis.alaska.edu/input/carl/
    ---------------------------------------------------------------
    _______________________________________________
    sac-help mailing list
    sac-help<at>iris.washington.edu
    http://www.iris.washington.edu/mailman/listinfo/sac-help


    • Hi Philip,

      Thanks, but that still leads to the issue of having the wrong headers.
      I am comparing source radiation at stations with different azimuths,
      so the headers need to be correct -- and, ideally, appropriate for a
      flat earth.

      It doesn't sound like turning of earth sphericity (or ellipticity) is
      an option, which is fine. I was just checking.

      Thanks,
      Carl

      On Mon, Jul 11, 2011 at 12:24 PM, Philip Crotwell <crotwell<at>seis.sc.edu> wrote:
      The easiest way might be to put the station and the event on the
      equator, then az and baz are 180 off each other and the ellipticity
      doesn't impact the distance.

      Philip

      On Fri, Jul 8, 2011 at 5:24 PM, Carl Tape <carltape<at>gi.alaska.edu> wrote:
      Dear sac-help:

      I am wanting to compare synthetic seismograms computed using a
      flat-earth model using two different techniques. It seems like it
      would be easiest to "turn off" the sphericity/ellipticity of the
      Earth, and then input the source and station locations in, say, km.
      And then the azimuth and back-azimuth angles would differ by exactly
      180 degrees. I do not see a sac header that might do this -- is there
      a simple solution? Alternatively, it seems I could set LCALDA = false,
      and then manually enter at least some information, but it would be
      safer to have sac to the computations based on input source and
      station locations.

      Thanks,
      Carl

      ---------------------------------------------------------------
      Carl Tape
      Assistant Professor
      Geophysical Institute
      University of Alaska Fairbanks
      Phone: 907-474-5456
      Email: carltape<at>gi.alaska.edu
      Web: http://www.giseis.alaska.edu/input/carl/
      ---------------------------------------------------------------
      _______________________________________________
      sac-help mailing list
      sac-help<at>iris.washington.edu
      http://www.iris.washington.edu/mailman/listinfo/sac-help



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