California has been doing a lot of shaking of late. In mid-June a sizable quake off its north coast triggered a tsunami warning, a false alarm, fortunately, while far to the south, earthquakes of lesser power knocked stuff off shelves and seriously rattled the composure of those who felt the ground sway beneath them. That's because the earthquakes that concern Californians most are those that haven't happened—at least, not yet—along the state's fault-fractured western edge. Of all those faults, the most feared is the San Andreas, which slashes its way along the California coast for 750 miles. Many scientists believe that after decades of quietude, the pressure on sections of the San Andreas is reaching the point at which something will have to give. Researchers have been rushing to instrument the fault—"setting out traplines," as Ken Hudnut, a geophysicist with the U.S. Geological Survey (USGS), puts it—to catch the faintest movements and seismic mutterings.
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