Jeff Freymueller, an assistant research professor of geophysics at the Geophysical Institute, tracks the fingernail-growth speed of Earth's plates with the help of satellites and Global Positioning System receivers. The Global Position System, GPS, is a system of 24 satellites operated by the U.S. Air Force Space Command at Peterson Air Force Base, Colorado. As all 24 satellites zip around the globe at an altitude of about 12,500 feet, they broadcast radio signals that are picked up by GPS receivers, some of which can fit in the palm of your hand. A computer within the GPS unit instantly compares the distances from the satellites to the receiver, then calculates the geometry and pinpoints the location of the GPS unit. Some airplane pilots and ocean-liner captains have called the GPS the greatest invention since the wheel.
Scientists find it useful, too.
About a dozen plates make up the Earth's crust. Alaska is a seismic hot spot because much of the state sits on or near where these plates meet. The Pacific Plate collides with and dives below the North American Plate along the Pacific coastline of Alaska. Movement of the plates in 1964 caused the Good Friday Earthquake. Each year, Freymueller and his colleagues travel to the same spots off the Seward and Sterling highways.