December 24, 2013
Scientists say they were able to forecast the size and location of an earthquake using GPS to study changes in the Earth’s shape.
The Nicoya Peninsula in Costa Rica is one of the few places where land sits atop the portion of a subduction zone where the Earth’s greatest earthquakes take place. That makes it a good spot for learning how large earthquakes rupture.
Subduction zones are locations where one tectonic plate is forced under another one and can often be the sites of devastating temblors. The magnitude 9.0 earthquake off the coast of Japan in 2011 was due to just such a subduction zone earthquake.
Because earthquakes greater than about magnitude 7.5 have occurred in this region roughly every 50 years, with the previous event striking in 1950, scientists have been preparing for this earthquake through a number of geophysical studies. The most recent study used 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, an associate professor in the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology.
Through a series of studies starting in the early 1990s using land-based tools, the researchers mapped regions where tectonic plates were completely locked along the subduction interface. Detailed geophysical observations of the region allowed the researchers to create an image of where the faults had locked.
The researchers published a study a few months before the Nicoya earthquake, describing the particular locked area with the clearest potential for the next large earthquake in the region. The team projected the total amount of energy that could have developed across that region and forecasted that if the locking remained similar since the last major earthquake in 1950, then there was likely enough energy for an earthquake on the order of magnitude 7.8 there.