News flash: In the summer of 1999, the residents of Washington State, British Columbia, and the surrounding area didn't experience a magnitude 6.7 earthquake.
That's right, they didn't feel a thing, although lower portions of the Earth's crust moved 20 millimeters. In a sudden surge, such a shift would have spawned an impressive quake, but the movement happened over a period of 6 to 15 days. Even seismometers in the area missed the motion because there wasn't any shaking going on. Only a Global Positioning System (GPS) network that continuously monitors surface motion in the region picked up the abnormal movement, says Herb Dragert of the Geological Survey of Canada in Sidney, British Columbia.