'Japan quake moved ocean floor 79 feet sideways'

'Japan quake moved ocean floor 79 feet sideways'

The immense amount of seismic stress that remain there following the March 11 earthquake has also put the region at risk of further powerful earthquakes, the researchers warned.

The journal Science has published three new papers about the effects and causes of the March 11 quake, which paints a picture of an earthquake hot spot much more complex and potentially dangerous than scientists had ever anticipated.

In one paper, the Japanese Coast Guard has released data from five geodetic instruments that in 2000-04 they had placed underwater along the fault line responsible for the colossal quake, the Daily Mail reported.

One of the instruments, according to the report, had actually been placed almost on top of the epicentre of the March-11 quake, at a station called MYGI.

Measurements taken in the week after the earthquake showed that at the MYGI site, the sea floor had moved about 79 feet to the east-southeast since the previous measurement in February. It had also risen about 10 feet.

Dr Mariko Sato, a geodesist with the Japan Coast Guard in Tokyo, believes almost all this movement happened during the quake.

"The scale is almost double that estimated only from the terrestrial data," Dr Sato was quoted as saying.

Under the seabed, the movement may have been even greater -- perhaps 160 to 200 feet, by some estimates.

In another study sure to raise alarm in Japan, scientists from the California Institute of Technology have reconstructed how the Tohuku-Oki earthquake unfolded using GPS data recorded at more than 1,200 sites.

Their data showed that -- contrary to previous opinion -- the area had built up massive amounts of strain prior to the earthquake.

Earlier, there had been general agreement among researchers that the "Miyagi segment" of the fault line was not under the stress of other segments along the Japan plate boundary, where large earthquakes occur at a regular basis.

But Professor Mark Simons' team showed that this assumption was deeply flawed. This raises questions about other sections of the fault line that had previously been considered low risk -- including areas further south, closer to Tokyo.

This "Ibaraki segment" of the plate boundary has been thought to behave in similar fashion to that of the Miyagi segment, and Professor Simons said it may likewise hold large amounts of seismic stress.

In recorded history, this southern area has experienced only one set of quakes larger than magnitude 8, which means the region could be ripe for its own rupture.

"We have to entertain the possibility this area can produce a large quake," Simons said. "This area will warrant a lot of attention in the near future."