Tectonic movement

[sabrinah]

if scientists know how much a tectonic plate moves each year why isn't it possible to accurately predict an earthquake?

[incitatus]

try an experiment...hold two erasers together, and slowly apply increasing force to slide them past each other. Try to predict when they will move. The answer is you can't. The tectonic plate movements are an average, but they move in jumps. One can say that such and such a plate is due a movement ( I think the San Andreas needs to move about 2ft to catch up to its average) but the friction between the plates, and their irregular profile makes it very hard to say when. The best one can do is monitor for increased local stress along the plate.