Japan's mega-quake struck in small zone of fault: study

June 15, 2011
A washed up house stands on the shoreline in Onagawa, Miyagi prefecture in April 2011. The deadly 9.0-magnitude quake that struck off northeastern Japan on March 11 ruptured a relatively small part of a notorious fault that straddles the Pacific seabed, Japanese scientists reported on Wednesday.

The deadly 9.0-magnitude quake that struck off northeastern Japan on March 11 ruptured a relatively small part of a notorious fault that straddles the Pacific seabed, Japanese scientists reported on Wednesday.

The earthquake occurred in part of the so-called Japan Trench, where the Pacific plate dives beneath the Okhotsk plate on which the Japanese archipelago lies.

Data supplied by a network of (GPS) stations, dotted across Japan and called GeoNet, have helped unlock details of where the quake took place and what happened.

Modelling of the stresses and strains placed upon Honshu island as the fault was torn apart indicates the epicentre was about 200 kilometres (120 miles) east of Sendai, at the heart of an extraordinarily compact, lozenge-shaped area of ocean floor.

Only a handful of earthquakes measuring 9.0 magnitude or more have ever been recorded, and they can rip open the over many hundreds of kilometres (miles).

The biggest quake ever detected, a 9.5-magnitude event that occurred off southern Chile in 1960, ruptured the for more than 1,000 kilometres (600 miles).

The March 11 quake, though, points to a slippage zone that measures 400 kms (250 miles) by 200 kms (120 miles) wide.

But what it lacked in size it more than compensated in terms of movement, for the energy release occurred less than 20 kms (12 miles) below the .

Birds sit on a wrecked car submerged in a river amid the tsunami devastation in Kesennuma, Miyagi prefecture in April 2011. The deadly 9.0-magnitude quake that struck off northeastern Japan on March 11 ruptured a relatively small part of a notorious fault that straddles the Pacific seabed, Japanese scientists reported on Wednesday.

The at the shifted by an astonishing 27 metres (88 feet), inflicting a water displacement which explains why the tsunami was so great.

The GeoNet system uses positioning sensors to provide millimetric mapping of land movements.

In the 15 years preceding the March 11 quake, the system showed a slow buildup of strain across Honshu as the mighty Pacific plate squeezed and dragged on the island's eastern flank.

The technology could be useful in monitoring faults where a massive quake occurs at gaps spanning centuries or even longer, after pent-up strain builds to breaking point.

Geological evidence from the distant past had suggested that the Japanese Trench was prone to massive, but very rare, tsunami-generating quakes.

But with the possible exception of a quake in AD 869, there was no documented evidence to support this suspicion, and so the risk was downplayed or ignored, says the study.

The paper, published in the British weekly science journal Nature, is lead-authored by Shinzaburo Ozawa of the Geospatial Information Authority of Japan, located in Tsukuba.

In a commentary, Jean-Philippe Avouac of the California Institute of Technology (Caletch) said that new data, from GeoNet and from sea-bottom pressure caused by the tsunami waves, indicated the epicentral slip on March 11 could be even more than 50 metres (165 feet).

If so, that would make it the biggest slip ever recorded, he said.

Explore further: New Sumatra quake takes seismologists by surprise

Related Stories

New Sumatra quake takes seismologists by surprise

October 1, 2009

The huge earthquake that hit Sumatra occurred at a deep, unexpected location, illustrating the dangerously complex geological mosaic in this area, a seismologist told AFP on Thursday.

Chile quake in 'elite class' like 2004 Asian quake

February 28, 2010

(AP) -- The huge earthquake that struck off the coast of Chile belongs to an "elite class" of mega earthquakes, experts said, and is similar to the 2004 Indian Ocean temblor that triggered deadly tsunami waves.

New findings on the developments of the earthquake disaster

March 16, 2011

The earthquake disaster on 11 March 2011 was an event of the century not only for Japan. With a magnitude of Mw = 8.9, it was one of the strongest earthquakes ever recorded worldwide. Particularly interesting is that here, ...

Recommended for you

Earth's mineralogy unique in the cosmos

August 26, 2015

New research from a team led by Carnegie's Robert Hazen predicts that Earth has more than 1,500 undiscovered minerals and that the exact mineral diversity of our planet is unique and could not be duplicated anywhere in the ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.