George Musser at Scientific American:
Things obviously get more interesting during earthquakes. “What the earthquake would do is the equivalent of what you do with a pair of scissors, if you cut diagonally across a map along a fault line and then slid one side of the map with respect to the other,” Hudnut says.
It never occurred to me that the co-ordinates on a map would change due to the earth itself moving, but it’s so obvious that it would. If you’re wondering, Australia has its own geocentric datum, called GDA94.