Deep quakes are harder to measure at close range. Within about six miles of a fault, there is a huge pulse of movement rather than a long series of wiggles. Though it's brief, that pulse can be devastating. One of the first recordings taken close to a big quake was at Loma Prieta. Later, seismograms from the Northridge and Kobe earthquakes showed the ground near the fault moving at more than three feet per second.
Quakes turn out to be more capricious than scientists had thought.
They can leap from one fault to another, vaulting three-mile gaps and ignoring geographical barriers that were once thought to confine them and limit their size.