I see that NGS benchmarks are used to monitor the movement of geologic plates.

Is one of the benchmarks assumed to be in a fixed location, with movements of all other benchmarks measured with respect to it, or are all benchmarks moving as a result of plate tectonics?


The IERS reference meridian is a weighted average of ground-based monitoring stations. Thus, tectonic monitoring must involve the motion of one's own plate relative to this global average motion.

  • @Kirk Thank you for responding with such alacrity! However, in order to encourage contributions, it might be a good idea in general to hold off for a few days before accepting responses. I for one would love to have someone come along with an amplification or critical remarks or even a totally different answer, especially anyone with direct experience in tectonic monitoring. – whuber Oct 20 '10 at 21:27
  • 1
    Ok, sounds good. Also realized this only answers the longitude aspect. I presume this meridian begins/ends at the poles of rotation. Can we assume that the poles of rotation are always at +/- 90 degrees with respect to GPS? – Kirk Kuykendall Oct 21 '10 at 19:35
  • 1
    @Kirk These systems are geocentric. After establishing a meridian, the only thing left is to determine the earth's orientation (which precesses slowly, which means time is an essential parameter in any high-accuracy reference system). The orientation of the earth's axis is defined with reference to a celestial reference system. Some information is available at itrf.ensg.ign.fr/itrs_itrf.php . – whuber Oct 21 '10 at 19:58
  • interesting, I wonder if this celestial reference system is what this guy needs gis.stackexchange.com/questions/2459/… I get a strange error for the php link you posted, is it a public site? – Kirk Kuykendall Oct 22 '10 at 15:40
  • @Kirk I'm getting that error now too. It was a public site yesterday! Just back up to itrf.ensg.ign.fr and follow a sequence of links labeled "ITRS and ITRF". – whuber Oct 22 '10 at 15:47

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.