National Geographic : 1995 Apr
ttle crust several miles under the surface, quakes send a series of seismic waves pulsing through nearby rock. Surface shaking can be muted / by stiff formations like granite or schist, which absorb much of the quake's energy. But shaking can be mag nified in sedimentary basins. Also soft, wet soils may liquefy during a quake. With each successive wave the earth becomes more like quicksand, weakening sup port for heavy structures. A model for disaster Twelve million people live in the L.A. area, where a quake three times as powerful as Northridge is likely to hit in the next 30 years. A model of ground shaking from such a quake on the Elysian Park Fault (above) shows a danger zone based on proximity to the fault, not to the epicenter the surface point above where the quake starts. "You could be miles from the epicenter and still be on top of the quake if you're right on the fault," says the U. S. Geological Survey's Lucile Jones.