Mon, Mar 14, 2011 - Page 5 News List

JAPAN DISASTER: Quake moved Japan by 2.4m: USGS

PRESSURE POINT:The Pacific plate pushes under the North American plate at a rate of about 83mm per year, but a huge earthquake can move the plates even more


Japan’s recent massive earthquake, one of the largest ever recorded, appears to have moved the island by about 2.4m, the US Geological Survey (USGS) said on Saturday.

“That’s a reasonable number,” USGS seismologist Paul Earle said. “Eight feet, that’s certainly going to be in the ballpark.”

Friday’s magnitude 8.9 quake unleashed a terrifying tsunami that engulfed towns and cities on Japan’s northeastern coast, -destroying everything in its path.

The quake and its tectonic shift resulted from “thrust faulting” along the boundary of the Pacific and North America plates, according to the USGS.

The Pacific plate pushes under a far western wedge of the North America plate at the rate of about 83mm per year, but a colossal earthquake can provide enough of a jolt to dramatically move the plates, with catastrophic consequences.

“With an earthquake this large, you can get these huge ground shifts,” Earle said. “On the actual fault you can get 20m of relative movement, on the two sides of the fault.”

He said similar movements would have been seen in recent earthquakes in Chile and Indonesia.

In December 2004, a magnitude 9.1 quake off Sumatra caused a tsunami that killed an estimated 228,000 people. An 8.8 quake off the coast of Chile in February last year killed more than 500.

There was not a similar ground shift in the magnitude 7.0 earthquake that devastated Haiti in February last year, Earle said.

“A magnitude 7.0 is much smaller than the earthquake that just happened in Japan,” he said. “We’ve had aftershocks [in Japan] larger than the Haiti earthquake.”

Kenneth Hudnut, a USGS geophysicist, said experts read data, including from global positioning systems, to determine the extent of the shift.

“We know that one GPS station moved [2.4m] and we have seen a map from GSI (Geospatial Information Authority) in Japan showing the pattern of shift over a large area is consistent with about that much shift of the land mass,” he told CNN.

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