Filthy_Rich said:
that's not true. the "big one" is expected to hit within the next 30 years, but that's all speculation. it may never happen; tomorrow; 10 years; 100 years. THere's no predicting it. Also, the whole "the longer it takes to hit, the larger it's gonne be" theory is bullshit.
Are you aware of how earthquakes work? In this region? Basically the far west coast is slowly moving upward, tugging on the plate to the right of it, causing tension. When the plate on the right side reaches its maximum "stretching" point, it's going to rebound back to its original shape, causing an earthquake. Therefore, the longer the left plate tugs on the right plate, the more the right plate will have to readjust itself, hence a larger earthquake.
Predictions can be made (though vague) because this is a continual pattern in California geology. You can go out to the faults and see them displaced by several feet where the left plate has moved north. Earthquakes are very difficult to detect, but long-term predictions are easier than short-term predictions.
And the whole probability thing comes from the USGS, so it's probably more accurate than you think.