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This is MORNING EDITION from NPR News. I'm Renee Montagne.

The earthquake that struck Japan several weeks ago will be remembered mainly for the devastating tsunami that it created. The quake itself did remarkably little damage to buildings in most areas, thanks to strict construction codes. But in a few places, particularly around Tokyo, buildings didn't fare so well. As NPR's Jon Hamilton reports, these are places built on land reclaimed from the sea.

JON HAMILTON: When the ground began to shake at Shoppers Plaza near Tokyo people got outside in a hurry. A video shows them milling about on a paved courtyard, waiting for the aftershocks to end.

(Soundbite of screaming)

Then, sections of the courtyard begin to pulse and heave. The pavement buckles, black liquid flows up through the cracks. Teiko Kato was there. She had just run out of the flower shop she manages, carrying the store's most valuable orchid.

Ms. TEIKO KATO (Owner, flower shop): (Through translator) I really witnessed to when the ground was moving sideways. And we thought that we cannot stand up there, so we moved farther down to closer to that bus stop.

HAMILTON: Within a few minutes, mud covered much of the courtyard. In places, the ground level dropped as much as a foot. Out on the street, manholes were being pushed up out of the earth. Water pipes broke. Utility poles began to lean.

Ms. KATO: (Foreign language spoken)

HAMILTON: Kato says she was terrified because she knew what was going on. It was more than an earthquake. The ground beneath her had become liquid. It's called liquefaction. The shaking allows sand and water underground to rise and things on the surface to sink.

Kato's shop and everything around it is built on land that used to be part of Tokyo Bay, and this sort of reclaimed land is highly vulnerable to liquefaction. But it's also cheaper to live here, so Kato and her family had moved in despite the risk.

Ms. KATO: (Through translator) We came in with a dream to have a new shining life in a nice area. But I don't know, after experiencing this.

HAMILTON: Since the earthquake, a lot of engineers have been visiting this area called Urayasu to figure out precisely what happened. Ross Boulanger spent several days there before returning to his job at the University of California, Davis. He says what happened is like what happens when you mix beach sand and water in a pail and shake it.

Dr. ROSS BOULANGER (Civil engineer, University of California, Davis): Soil takes on the appearance of being like a liquid, and that's where the term liquefaction comes from.

HAMILTON: Boulanger has studied liquefaction from the 1989 Loma Prieta earthquake in California. It affected San Francisco's Marina District, which is also built on reclaimed land.

But Boulanger says what he saw near Tokyo bay was much worse. That's because the Japanese earthquake was more powerful and went on for a very long time.

Dr. BOULANGER: If you look at by comparison the motions in the Marina District from the Loma Prieta earthquake, strong shaking was over in 10 or 15 seconds, whereas at some of these sites the shaking is going on for minutes.

HAMILTON: Boulanger says that may be the reason even small houses in Urayasu were damaged. Usually these houses are so light they tend to float, even as the ground liquefies.

Dr. BOULANGER: You know, one of the things we'd never really seen before were very light structures settling and tilting by amounts we hadn't really seen in other earthquakes.

Unidentified Man: (Foreign language spoken)

(Soundbite of shoveling)

HAMILTON: Takako Utsunomiya lives in one of those structures. It's a two-story home in a nice part of Urayasu, not far from Tokyo Disneyland. Utsunomiya is sweeping the path from her front door as two masked workers shovel mud from a walkway beside the house. The house is still intact on its concrete slab foundation, but you might not want to live in it.

Ms. TAKAKO UTSUNOMIYA: (Through translator) My house was heavily damaged, because it's really tilted and distorted towards the back side of the land. And if you're standing in the house you feel dizzy because the floor is distorted.

HAMILTON: Engineers say there was much less damage at nearby Tokyo Disneyland, which is also built on reclaimed land. They say that's because Disney spent a lot of money to pack down the reclaimed land before building their theme park on it.

Jon Hamilton, NPR News.

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