The Okinawa and Ogasawara island chains are among 17 areas around the world that are at risk of being hit by magnitude-9 class earthquakes, based on estimates of seismic energy stored underground, scientists said.
The Okinawa and Ogasawara island chains are among 17 areas around the world that are at risk of being hit by magnitude-9 class earthquakes, based on estimates of seismic energy stored underground, scientists said.
"I wouldn't be surprised if an M9-class earthquake were to strike any of the areas shown in our results, although our method has yet to be verified," said Ryoya Ikuta, an assistant professor of seismology at Shizuoka University, who conducted the research.
The findings will be presented at a meeting of the Seismological Society of Japan, which is scheduled to open on Oct. 7.
The Earth's surface is divided into a number of tectonic plates. A migrating plate pulls a continental plate downward as it dives beneath the latter along a plate boundary, a process that accumulates rebound energy in the continental plate. Earthquakes are believed to occur when such a rebound releases energy.
Ikuta and his co-workers used geological survey results, Global Positioning System measurements and other available data to calculate plate motion speeds, which they then used to estimate the distances of plate subduction over a 111-year period from 1900 through 2010.
They also used the records of 9,248 earthquakes from the same period in a catalog kept by the International Seismological Center in Britain to calculate the distances of plate rebounds. The differences were used to estimate how much energy is stored.
The researchers found the accumulated subduction lengths and the energy being stored were large enough to cause a giant, magnitude-9 class earthquake in 17 areas of the world.
In Japan, they include the Nansei island chain, which covers the Okinawa islands, the Ogasawara Islands and areas along the Pacific coast of Hokkaido.
While all those areas are known to be prone to earthquakes, previous research has typically relied on historical records to forecast seismic events and their magnitudes expected in those areas.