4 ms·

I noticed in the article: "Mayotte is on the move. Since mid-July, GPS stations on the island have tracked it sliding more than 2.4 inches to the east and 1.2

by jrd259 8y ago

I noticed in the article: "Mayotte is on the move. Since mid-July, GPS stations on the island have tracked it sliding more than 2.4 inches to the east and 1.2 inches to the south." If this isn't a mistake, it's also very interesting. 2.7 inches in four months is very fast. That's 20 cm/year. The fastest techtonic plates move about 10 cm/year. Also this island does not appear to be near a plate boundary, so what could make it move? The article didn't say what it was moving relative to.

Flozzin 8y ago
"the agency estimates that a magma body that measures about a third of a cubic mile is squishing its way through the subsurface near Mayotte." Since it's a magma body moving Mayotte, Mayotte could be moving relative to it's place on the plate?
JoeAltmaier 8y ago
Sure it did - relative to the GPS coordinate system.
- jhayward 8y ago
  Just because one uses GPS to measure position does not mean one is calculating position in WGS84, the GPS native geodetic datum. For instance many survey instruments use Differential GPS to obtain a more precise location by using corrections from a receiver at a well-established survey mark. When using DGPS the coordinate system becomes that of the reference mark, not the GPS system. So I think the question is relevant, and takes note of the context in which ground motion is studied.
  - JoeAltmaier 8y ago
    But that ground point is located by GPS as well, which translates the more-precise location relative to the ground point right back to the WGS84 frame
    - jhayward 8y ago
      No, the ground point is most often registered in either a continental or regional plate datum.
      - JoeAltmaier 8y ago
        'Most often'? By whom? These things are in use in the 100's of thousands in agriculture now. Such base stations record their ground point by GPS location.
lostlogin 8y ago
That is a large amount. I don’t think the rate of tectonic plate movement relates to the amount of land movement very well though. New Zealand is shuffling around all over the place in silent quakes by about that much, and in the not-at-all-silent quakes it’s been metres of movement. The last decade has been rather wobbly.
gus_massa 8y ago
From https://en.wikipedia.org/wiki/2010_Chile_earthquake https://en.wikipedia.org/wiki/2010_Chile_earthquake > [After the 2010 Chile earthquake] A research collaborative of Ohio State and other institutions have found, using GPS, that the earthquake [...] moved Concepción at least 3 metres (10 ft) to the west. [...] Several cities south of Cobquecura were also raised, by up to 3 meters.
SirLuxuryYacht 8y ago
Local geology can play a pretty big role in observed velocities, but I agree these are pretty quick. The velocity changes in the figures are really interesting, and I agree much faster than plate motions. I'd wager that there is some kind of slow or aseismic slip happening. Slow slip events There are notes on the displacement time series though they are in french. http://volcano.iterre.fr/mayotte-seismo-volcanic-crisis http://volcano.iterre.fr/mayotte-seismo-volcanic-crisis

by jrd259 8y ago

Flozzin 8y ago

"the agency estimates that a magma body that measures about a third of a cubic mile is squishing its way through the subsurface near Mayotte." Since it's a magma body moving Mayotte, Mayotte could be moving relative to it's place on the plate?

JoeAltmaier 8y ago

Sure it did - relative to the GPS coordinate system.

jhayward 8y ago
Just because one uses GPS to measure position does not mean one is calculating position in WGS84, the GPS native geodetic datum. For instance many survey instruments use Differential GPS to obtain a more precise location by using corrections from a receiver at a well-established survey mark. When using DGPS the coordinate system becomes that of the reference mark, not the GPS system. So I think the question is relevant, and takes note of the context in which ground motion is studied.
- JoeAltmaier 8y ago
  But that ground point is located by GPS as well, which translates the more-precise location relative to the ground point right back to the WGS84 frame
  - jhayward 8y ago
    No, the ground point is most often registered in either a continental or regional plate datum.
    - JoeAltmaier 8y ago
      'Most often'? By whom? These things are in use in the 100's of thousands in agriculture now. Such base stations record their ground point by GPS location.

lostlogin 8y ago

That is a large amount. I don’t think the rate of tectonic plate movement relates to the amount of land movement very well though. New Zealand is shuffling around all over the place in silent quakes by about that much, and in the not-at-all-silent quakes it’s been metres of movement. The last decade has been rather wobbly.

gus_massa 8y ago

From https://en.wikipedia.org/wiki/2010_Chile_earthquake https://en.wikipedia.org/wiki/2010_Chile_earthquake > [After the 2010 Chile earthquake] A research collaborative of Ohio State and other institutions have found, using GPS, that the earthquake [...] moved Concepción at least 3 metres (10 ft) to the west. [...] Several cities south of Cobquecura were also raised, by up to 3 meters.

SirLuxuryYacht 8y ago

Local geology can play a pretty big role in observed velocities, but I agree these are pretty quick. The velocity changes in the figures are really interesting, and I agree much faster than plate motions. I'd wager that there is some kind of slow or aseismic slip happening. Slow slip events There are notes on the displacement time series though they are in french. http://volcano.iterre.fr/mayotte-seismo-volcanic-crisis http://volcano.iterre.fr/mayotte-seismo-volcanic-crisis