[Award Winner] Using tectonic plates to draw a world map

[HandsomeRob]

It may be important to remember that plate motion can't really be described by simply drawing an arrow on the plate and saying "it moves that way." Actual plate motion is actually a rotation around a point on the earth's surface. What you really need to know for this exercise is relative motion; it is completely possible to say that plate 1 is moving west (with respect to plate 2) and at the same time moving east (with respect to plate 3). This situation happens all the time.

Here is a quick tutorial on velocity space analysis:
Say you have a situation like in the first attachment here. Plates A and C are moving toward each other at a rate of 4 cm/yr. Plates A and B are moving away from each other at a rate of 3 cm/yr. What is the motion between plates B and C?

Construct a velocity space diagram to find out (see second attachment). Since plate B is moving west at 3 cm/yr (with respect to plate A), place a point for B 3 units to the west of A. Since plate C is moving south at 4 cm/yr (again, with respect to plate A), place a point for C 4 units to the south of A. Now it should be clear that plate C is moving southeast at 5 cm/yr with respect to plate B, as the point for C is 5 units to the southeast of the point for B.

This means that the B/C boundary is convergent, with an element of right-lateral strike-slip motion as well. The third attachment here shows the solution.


I hope some of that a) makes sense and b) helps.
-Rob