Japan quake may have caused plate shift

TOKYO, June 15 (UPI) -- Global positioning system data indicated a seismic shift occurred from the March 11 earthquake that devastated northeastern Japan, research indicates.

The 9-magnitude earthquake that shook Japan eased strain from the Japanese trench that had accumulated over hundreds of years, said the report published Wednesday on Nature's Web site.

The findings support the importance of GPS observations when assessing future earthquake potential, the authors said.

To better understand the potential of major earthquakes, Shinzaburo Ozawa of the Geospatial Information Authority of Japan and his colleagues used GPS data to assess the mega-thrust fault off the coast of Japan. Data indicated the coseismic slip area -- the ground deformed during the earthquake -- stretched about 248 miles along the Japan trench, Ozawa said.

Strain on tectonic plates in the region has been higher than normal recently, but the release of the strain during the earthquake partially resolved the issue, Ozawa said.

The researchers said the afterslip (slow earthquakes and aftershocks) is spreading into the coseismic slip area, expanding into the surrounding region and going about 62 miles deep, and could be an avenue of release for the remaining strain energy.