. >>> one of the dangers posed by earthquakes is liquefaction. liquefaction happens when strong shaking loosens the ground soil sending water and mud spewing to the surface. homeowners in new zealand are learning something else, if it's happened once, it will happen again. nhk is reporting from christchurch. >> reporter: walking the empty street near her home, sue holmes is alone. no cars on the road, no children in the yards, no people in the houses. >> it's like walking through a ghost town. this general was a retired car salesman with his wife. now everybody is gone. >> reporter: the liquefaction has turned holmes' neighborhood into a scene of desolation. some 40 families used to live here. now there are just two. >> we had a big sign there so people will know we're still here. >> reporter: holmes wants to stay. christchurch is her hometown, but she's faced with a disaster that never seems to end. christchurch seems to be a city under siege. earthquakes have shaken the surrounding area in the last year and a half. buildings in ruins and many s

liquefaction, liquefaction is a term they use when the ground is loose. usually when structures or infrastructure is built on sand or land fill, something that's not solid, what happens is in shaking, during an earthquake, the earth that's very loose, that sand or land fill, acts like water. this is sand, sand and water coming up through a hole. in japan, all these buildings were built on liquefaction. i forget what year this was, but it was one of the bigger earthquakes. 7 story buildings built on liquefaction. the amount of time the earth shook, the earth became liquid and as it became liquid, the building sank into it until it stopped. when it stopped it just fell over. light damage buildings, superficial damage, broken windows, some plaster that might be cracked but basically a light damage building would be one that has mostly damage to the contents. shelves falling over, windows broken, that type of thing. if you had to go into a light damaged building, you would use these procedures. of course you gather information about a building before you go i

such experiments also showed how liquefaction can cause the ground to shift sideways, a real problem if there's a bridge on top. >> when we're looking at liquefaction and the subsequent lateral spreading, we typically see that along riverbanks. where there's enough of a slope that, when the ground liquefies, you essentially have a slope failure. and you can have several meters of movement of the ground toward the river. now, when that ground moves, it tends to bring the bridge foundation with it. and that can essentially rip apart the bridge. >> reporter: the oregon department of transportation has spent more than 20 years working on ways to minimize earthquake damage and damage from the tsunami that will follow. but they've only managed to retrofit about 100 out of 1,100 bridges at risk. highway division administrator paul mather. >> virtually every bridge in western oregon is at risk. thas the i-5 corridor, that's all of 101, and every bridge that connects those corridors in the state highway system, but there's also the local system as well as private bridges that we have in weste

such experiments also showed how liquefaction can cause the ground to shift sideways, a real problemthere's a bridge on top. >> when we're looking at liquefaction and the subsequent lateral spreading, we typically see that along riverbanks. where there's enough of a slope that, when the ground liquefies, you essentially have a slope failure. and you can have several meters of movement of the ground toward the river. now, when that ground moves, it tends to bring the bridge foundation with . and that can esseially rip apart the bridge. >> reporter: the oregon department of transportation has spent more than 20 years working on ways to minimize earthquake damage and damage from the tsunami that will follow. but they've only managed to retrofit about 100 out of 1,100 bridges at risk. highway division administrator paul mather. >> virtually every bridge in western oregon is at risk. that's the i-5 corridor, that's all of 101, and every bridge that connects those corridors in the state highway system, but there's also the local system as well as private bridges that we have in western ore

there was a lot of water damage we might have even had some liquefaction soil failure. we had a major failure. >> that's right. this tribute goes all the way to golden gate. this is in a mountain lake and beyond ththat, it was a surface flow. this is a reservoir. on my right is this defensive the positive dune sand. the wind blows, it comes from the ocean beach. because the sand is moving, you can see evidence along this side of the hill in 1989. the vibrations in accelerated. you have a significant amount of movement to the point that the homes that uc had very severe damage for two blocks. we recognized what the problem was at the time, it was a matter of loose sand on a very steep slope. thank you for the effort. we were able to get federal funding and design which you see in the upper walls. the lower walls was actually billed as part of the wpa. the upper wall was built in 1991-'92. this is a concrete wall and it has rocked going through the wall that extends the distance of 80 feet beyond the wall. the next earthquake occurs, the wall is designed to resist and the