# 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:
Carl Tape
2011-07-08 20:24:32
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
---------------------------------------------------------------

• 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
---------------------------------------------------------------
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• Carl Tape
2011-07-13 04:50:12
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