PNNL later took over the site's earthquake tracking. In the early 1980s, Hanford began studying the possibility of burying spent commercial reactor fuel deep at the site - an idea that was later discarded. But the project brought geologist Reidel, geophysicist Rohay and Hartshorn, a retired U.S. Air Force veteran who spent much of his career tracking underground nuclear explosions, to Hanford to track and study the site's tremors, quakes and geology. They took over the site's seismometers, which are essentially heavy magnetic metal cores encasing electrical wires. The contraptions are mounted on springs inside cases that stand anywhere from 1 to 2 feet tall.
Tremors jiggle the springs, which move the wires inside the core to produce an electrical current.
Radio signals send the data to a PNNL lab in northern Richland. To track earthquakes prior to 1969, Reidel and Rohay sometimes depend on news accounts, such as one detailing a magnitude 6 earthquake near Walla Walla in 1936. Even American Indian stories provide clues. An old Yakama story tells of a landslide killing Indians at an encampment a few hundred years ago, which could have been caused by earth tremors. Hanford's tiny earthquakes are caused by immense subterranean pressures.