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I'm doing some research about tectonic plates and at which speeds they move and in which directions, because I'm writing a program to simulate the movement of the tectonic plates and also calculate where they were at previous times and where they will be at some time in the future.

For this reason, I'm trying to find some good information about the speeds of the movement of the tectonic plates over the years and in which direction they were moving. I found one set of estimates here but I'm not exactly sure how accurate they are. I also found estimates on the Wikipedia pages for each of the plates, but it doesn't agree with the first estimate and I also want to know how significantly these speeds are changing over time (I assume the movement of the plates is not linear).

Finally, the first site doesn't give in which direction they are moving and Wikipedia does, but I don't quite understand it - it says, for example "west relative to the African plate", and I'm not sure what exactly that means.

Any help would be appreciated here. Thanks!

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    $\begingroup$ You may want to look into the existing plate motion models. The UNAVCO app lists a bunch, for instance. $\endgroup$ – mkennedy Nov 8 '16 at 21:37
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You will want to look at the GPlates program and its references to where it gets its data from. It is probably the most widely used repository to show plate motion information for the current time as well as far into the past.

As far as the "...relative to the African plate" part is concerned: If you are sitting somewhere on the moon, and look for long enough time (let's say, a few million or tens of millions of years), you will see plates move about over the surface of the earth. But because you only see the surface of the earth, you cannot distinguish the following two cases: (i) all plates move westward, (ii) the earth just rotates a wee bit slower than you thought. That's because you don't have a coordinate system that is anchored "in the Earth" (e.g., rotates at the same speed as the Earth core) with respect to which you can determine what moves where. As a consequence, all we can do is describe relative motions of plates. One convenient way to do this is to choose a coordinate system in which one of the plates remains stationary (e.g., the African plate) and all others move.

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Check out the USGS seismic data maps for each area of interest. For example, http://walrus.wr.usgs.gov/tsunami/samoa09/ gives you the relative speed and direction of the Pacific Plate relative to the Fiji-Tonga-Australian plate. The directional arrow on Figure 2 gives the mean relative motion in mm/year.

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  • $\begingroup$ What exactly does it mean "relative to the _ plate"? Also, does the speed/direction of the plates not change, or does it? (Sorry, I'm fairly new to all of this.) $\endgroup$ – heather Nov 7 '16 at 22:26
  • $\begingroup$ @heather movement is relative. If you are driving 60 and I'm driving 70, from your point of view I'm driving only 10. $\endgroup$ – Gimelist Nov 8 '16 at 7:40
  • $\begingroup$ The speed has to be averaged over several years because the plate motion is not uniform or continuous. Little relative motion takes place until the accumulating strain energy is enough to overcome the inter-plate friction. Then an earthquake occurs and a large plate motion happens in seconds. But even that is a simplification, because not all of the plate margin may move at once, whilst the strain energy induces some degree of plastic deformation. The same two plates can have different average velocities due to plasticity, variable gradient of the subduction zone, and spherical geometry. $\endgroup$ – Gordon Stanger Nov 8 '16 at 13:43

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