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Researchers explore quakes' shaky memories

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By Roger Snodgrass

A magnitude 7.4 earthquake centered in Yucca Valley, Calif., in 1992 jolted local residents at the time and continues to shake out new scientific findings. Called the Landers earthquake, after the closest town, the event triggered a number of other afterquakes across fault lines into Yellowstone in Wyoming and southern Montana.Los Alamos National Laboratory researcher Paul Johnson said this morning that he began reading about Landers quake about five years ago, but he was not satisfied with the explanations that were offered. When a colleague in Paris agreed with his hypothesis that a higher amplitude seismic wave might have been propagated that triggered quakes at a distance, he began serious work on the idea, but realized he needed experimental evidence.In a letter that appeared Thursday in the science journal Nature, Johnson and his colleagues, approaching the subject from a variety of disciplines, show how energy can be stored in certain types of granular materials like those found along fault lines worldwide. Each earthquake releases seismic waves or vibrations that travel through the Earth.