Cracks on the external walls of the Monsenor Sanabria hospital in Puntarenas, 90 km northwest of San Jose, on September 5, 2012, after a powerful 7.6-magnitude earthquake struck Costa Rica's Pacific coast. Seismologists working in the area had forecasted the possibility of such a quake. (Ezequiel Becerra/AFP/GettyImages)
On September 5, 2012, one plate of the Earth’s crust slipped below another 25 miles beneath the surface of Nicoya, Costa Rica, triggering a magnitude 7.6 earthquake. But unlike many other quakes, this one was not entirely a surprise.
Earthquakes of magnitude 7 or greater have occurred at this plate interface in 1853, 1900 and 1953. When the 1990s rolled around, scientists knew to expect another one sometime in the coming years. They began studying the region with ground-based GPS and seismic measurements, which led to accurate predictions of where an earthquake was likely to occur and that the quake would reach a maximum of magnitude 7.8.
The fault where the quake occurred is what’s known as a subduction zone, where one plate slides under another. The movement of the plates causes the Earth itself to change, allowing the team of scientists to track land movement and figure out areas of growing tension that will eventually be released in an earthquake, Andrew Newman, a Georgia Institute of Technology associate professor and one author of a new study detailing the research, told weather.com. The plates are in a state seismologists call “locked up.”
Andrew Newman performs a GPS survey in Costa Rica's Nicoya Peninsula in 2010. (Lujia Feng)
“Where that fault locked up starts to build energy for future earthquakes, but what it also tends to do is deform the land,” Newman said. “So we used the deformation of the land to map out the area that’s locked up.”
The Nicoya Peninsula is geologically rare in that a vast majority of subduction zones — more than 90 percent, Newman said — are not under land, but under water, such as the Cascadia zone off the Pacific Northwest of the United States or the Tohoku region of Japan, where a massive magnitude 9 earthquake triggered a devastating tsunami in March 2011. Cascadia “is capable of unleashing a similarly sized quake,” according to a release.
Newman hopes to continue studying the Nicoya Peninsula’s response to the 2012 earthquake, which would allow seismologists to better understand how energy builds up again after an earthquake. The research helps to demonstrate the importance of taking such measurements in understanding where big earthquakes will strike next, he said. “All we need to do is make detailed images of how the Earth is deforming in subduction zones underwater,” he added, “and we can really start mapping out the areas that are building up energy for release in future earthquakes.”
The research was published in the journal Nature Geoscience.
India: Sept. 29, 1993
The first of two of the top-10 deadliest earthquakes of the last 25 years that occurred in India was a 6.2 temblor that killed 9,748, according to the USGS. (DOUGLAS E. CURRAN/AFP/Getty Images)