Scientists predicted size, location of 2012 Costa Rica earthquake
“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 Susan Schwartz, professor of earth sciences at the University of California, Santa Cruz, and a co-author of the study.
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 release notes that 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. 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 is presently enough energy for an earthquake on the order of magnitude 7.8 there.
Because of limits in technology and scientific understanding about processes controlling fault locking and release, scientists cannot say much about precisely where or when earthquakes will occur. Earthquakes in Nicoya, however, have occurred about every 50 years, so seismologists had been anticipating another one around 2000, give or take twenty years, Newman said. The earthquake occurred in September of 2012 as a magnitude 7.6 quake.
“It occurred right in the area we determined to be locked and it had almost the size we expected,” Newman said.
The researchers hope to apply what they’ve learned in Costa Rica to other environments. Virtually every damaging subduction zone earthquake occurs far offshore.
“Nicoya is the only place on Earth where we’ve actually been able to get a very accurate image of the locked patch because it occurs directly under land,” Newman said. “If we really want to understand the seismic potential for most of the world, we have to go offshore.”
Scientists have been able to reasonably map portions of these locked areas offshore using data on land, but the resolution is poor, particularly in the regions that are most responsible for generating tsunamis, Newman said. He hopes that his group’s work in Nicoya will be a driver for geodetic studies on the seafloor to observe such Earth deformation. These seafloor geodetic studies are rare and expensive today.
“If we want to understand the potential for large earthquakes, then we really need to start doing more seafloor observations,” Newman said. “It’s a growing push in our community and this study highlights the type of results that one might be able to obtain for most other dangerous environments, including offshore the Pacific Northwest.”
The research was supported by the National Science Foundation and was a collaboration of researchers from Georgia Tech, the Costa Rica Volcanological and Seismological Observatory (OVSICORI) at Universidad Nacional, University California, Santa Cruz, and the University of South Florida.
— Read more in Marino Protti etal., “Nicoya earthquake rupture anticipated by geodetic measurement of the locked plate interface,” Nature Geoscience (22 December 2013) (doi:10.1038/ngeo2038)
