"Plate boundary earthquakes happen every 100 years or so, but one of this magnitude happens only once in 1,000 years," Oki said.
Yuji Yagi, associate professor at Tsukuba University, said an earthquake of this scale could trigger other earthquakes at faults that are already on the brink of a tectonic upheaval.
"The stress created by a massive quake increases the possibility of other large tremors; extreme caution is needed," he said.
Sadayuki Kitagawa, an officer at the seismic research division of the government’s Earthquake Research Promotion headquarters, said that while they had envisioned a smaller earthquake occurring on the coast of Fukushima or Ibaraki prefectures, they did not expect one so close to land and of such intensity.
"We were predicting an earthquake with a magnitude of 8 or smaller, not one this big," he said, adding that the scale of Friday’s quake caused an unusually large series of aftershocks that was expected to last for a while.
Kitagawa said Friday’s magnitude-8.8 earthquake was close in size to the 2004 earthquake off Sumatra that generated the huge Indian Ocean tsunami.
Bloomberg News on Saturday reported an Italian geological institute as saying Japan’s strongest earthquake probably shifted the Earth’s axis by about 10 cm.
Read the rest of the story: Seabed split; quake tilted Earth’s axis 10 cm.