Who's gonna prove them wrong?
I just find it hard to believe these small values can be measured reliably.
> http://news.yahoo.com/big-earthquakes-create-global-scale-gps-errors-144104992.htmlbr >
Glad you posted that. I saw the story and was going to post it myself. Very interesting.
Larry P
And So You Did, But It Is A Non-Problem
Users of long range GPS calculations are in no position to calculate offsets as suggested in the article.
Do they not realize that every GPS station is always moving and it's position is constantly being recalculated by the GPS community experts?
Are they complaining because they cannot get a precise new observation immediately after an earthquake, too bad? The required calculations and adjustments take considerable time after a sufficient number of observations. Weeks or months may be required for the position precisions they desire. They will have to store their data and reprocess with backward regressive software.
Paul in PA
And So You Did, But It Is A Non-Problem
For those that are interested here is a link to the original article:
http://rses.anu.edu.au/geodynamics/tregoning/50.pdf
They aren't complaining at all. They are showing that after an earth quake occurs the previous reference frame is no longer accurate. Part of a reference frame is a velocity model so that we can compare data collected at two different epochs. These velocity models make the assumption that stations are moving linearly, for example in central USA stations are moving about 2mm/year in the east direction and a little bit in the north and up direction.
The researchers showed that if an earthquake occurs in Australia this can change the velocity that a station is moving even in north america. And over time, if we do not update the reference frame, we can no longer confidently use these station velocities to compare data collected at different epochs.
As to why it is a "non-problem" for most:
1) differential users won't be affected as long as your reference station is nearby;
2) it will take a while for cm level errors to appear and by that time...see (3)
3) we have experts at our national geodetic agencies doing this type of research and updating our reference frames, and CORS coordinates, sometimes at great annoyance to users :).
And So You Did, But It Is A Non-Problem
Actually most of the eastern U.S. (east of western Nevada) is moving generally SW at approximately 1.5 cm per year. Motions in the "up" direction are most often quite localized, areas around the Gulf coast and Chesapeake Bay are sinking while some of the most northern parts are uplifting around a mm per year.
