Using GPS to study changes in the Earth's shape allowed a forecast of the size and location of a 2012 magnitude 7.6 earthquake in Costa Rica, scientists report. Because earthquakes greater than about magnitude 7.5 have occurred on Nicoya Peninsula about every 50 years, with the previous event striking in 1950, scientists were ready with GPS to map out the area along the fault storing energy for release in a large earthquake. "This is the first place where we've been able to map out the likely extent of an earthquake rupture along the subduction megathrust beforehand," said Andrew Newman, a professor in the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology. U.S. and Costa Rican researchers took part in the study of the subduction zone, a location where one tectonic plate is forced under another one. "The Nicoya Peninsula is an ideal natural lab for studying these events, because the coastline geometry uniquely allows us to get our equipment close to the zone of active strain accumulation," said study co-author Susan Schwartz, professor of earth sciences at the University of California, Santa Cruz. The researchers published a study a few months before the earthquake, describing the particular locked patch with the clearest potential for the next large earthquake in the region. Subsequent events proved them right, they said in a report of their study in the journal Nature Geoscience. "It occurred right in the area we determined to be locked and it had almost the size we expected," Newman said.