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The magnetic North (or South) Pole moves due to activities in the inner of Earth. And earthquakes can tilt the Earth's orientation a tiny bit. But can and does the axis' orientation relative to the surface change too? A major impact could surely do it, but could the Earth's inner activities?

I don't mean precession, nor tectonics or continental drift, but the movement of the rotation axis. Could for example the geographic North Pole move to Greenland? (Not Greenland moving to the NP)

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  • $\begingroup$ Do you mean precession? link one link two $\endgroup$ – Gimelist Mar 25 '16 at 9:48
  • $\begingroup$ @Michael No, I don't mean precession. Precession means that the entire Earth changes its tilt. The geographic North Pole remains in the same geographical place. I will try to clarify. $\endgroup$ – LocalFluff Mar 25 '16 at 10:17
  • $\begingroup$ @LocalFluff: Except that thanks to plate tectonics, that "same geographical place" moves about - which means that not only was the North Pole not always in the middle of the Arctic Ocean, there wasn't always an Arctic Ocean. $\endgroup$ – jamesqf Mar 25 '16 at 17:55
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Yes, it's called polar motion.

The rotational pole moves continuously, as you can see from the right-hand side of this figure (below) by the Earth Orientation Centre (EOC) and the International Earth Rotation and Reference Systems Service (IERS). The figure shows about 650 days of time; mjd is modified Julian day and time goes along the locus in the polar motion diagram.

The daily polar motion

The left-hand side of the figure shows Length of Day, and I think that's chiefly why they are making these refined polar measurements — to keep track of leap seconds, etc.

It's been established, by Fong et al. (19996), among others, that earthquakes could change the earth's rotational axis, by redistributing mass on a large scale. Their table 1 shows [the sort of effect that individual earthquakes theoretically have — edited after comment from David Hammen] on the length of day; $\Psi$ is the excitation vector:

Table 1 from Fong et al 1996

The EOC's website lists other geophysical excitations, among them:

  • Atmospheric angular momentum
  • Oceanic angular momentum
  • Hydrological excitation function
  • Axial angular momentum of the core

References

Chao, Benjamin Fong, Richard S. Gross, Yan-Ben Han (1996). Seismic excitation of the polar motion, 1977–1993. Pure and Applied Geophysics, September 1996, Volume 146, Issue 3, pp 407-419. DOI 10.1007/BF00874727

Update: This article on some new research in this field is worth a read.

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  • $\begingroup$ Note well: The change in the Earth's rotational axis due to even the strongest of earthquakes is purely theoretical. The noise in the geophysical excitations is orders of magnitude larger than is the tiny change due to the an extremely large earthquake. $\endgroup$ – David Hammen Mar 25 '16 at 14:23
  • $\begingroup$ @David: Fair point; I modulated the language a bit. Cheers! $\endgroup$ – kwinkunks Mar 25 '16 at 17:30
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@kwinkunks already gave a good answer on the short time scale. On long time scales, mantle convection and plate tectonics redistributes large amounts of mass, and the conservation of angular momentum requires that the direction and speed or rotation of the Earth changes accordingly. (This is independent of the fact that the orientation of Earth's axis may stay put but continents may move over it, changing the "apparent" location of the poles.)

Changing mass distribution because of mantle convection also indices torques on the Earth due to coupling with the rotation of the moon around Earth, and the Earth around the Sun. This, too, over time leads to changes of the Earth axis's direction.

Both of these effects act on time scales of tens of millions of years.

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