National Geographic : 1995 Apr
Anatomy of an earthquake Like a brush fire jumping a highway, the rupture that caused the 7.3 Landers earthquake in June 1992 hopped from fault to fault as it tore through the California desert. Darker reds in this view (right) highlight areas of greatest fault slippage as the rupture radiates out from the hypocenter-the point where the earthquake started, several miles under the epicenter. ILLUSTRATIONSBYCHUCKCARTER Camp Rock Emerson Faults 121 sec 116 seconds 11seconds 6seconds 11 second The quake's chronology While other earthquakes have been known to "step over" to adjacent faults, the Landers quake was the first where researchers could track the slippage (above, in red). The rupture, which is plotted in five-second intervals, traveled 43 miles in 24 seconds. BASEDON A MODELBY DAVID J. WALD USGS, PASADENA Seismic waves Earthquakes emit primary waves (top), which expand and contract the earth's crust. The more powerful secondary waves move more slowly, shaking the ground as they pass through the rock.