[Partisan Gunslinger]

They kind of shuffle around, slowly, each at their own pace, and when two of them collide, rock either goes up or goes down, in fits and starts, and you get earthquakes. Mostly concentrated near where plates meet. But there just isn’t anything to force earthquakes all at once, everywhere, unless a gigantic astral body collides with Earth, and if that happens, earthquakes are the least of our problems.

It's more complicated than that. The magnetic field of the earth acts funny when there's a big earthquake. There's more to it than just two rocks colliding.

[yefragetuwrabrumuy]

Changes in the magnetic field are just a small side effect. Bottom line, there isn’t going to be any May 21st cataclysm. Massive geological forces, when they do happen, usually build up for a very long time, and give all sorts of indications.

Something of the scale to cause worldwide earthquakes would have to be immensely larger than the supervolcano that covered India with lava in the distant past. Literally, the majority of the Earth’s mantle would have to be involved.