PETER MENZEL / SCIENCE PHOTO LIBRARY PETER MENZEL / SCIENCE PHOTO LIBRARY
Earthquake research: banks of traditional seismometers in a laboratory at the U.S. Geological Survey, Menlo Park, California. USGS seismologists have predicted that an earthquake of around magnitude 6 will occur on the San Andreas fault at Parkfield, California, before 1993. Dozens of researchers have made Parkfield village the most heavily instrumented earthquake region in the world. Data from various instruments is analysed to determine the probability of a quake within 72 hours. Seismometers measure the vibrations that result from the abrupt movement of rocks aside faults - planar breaks in the rocks of the Earth's crust.
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