Earthquake in Japan would not have caused such catastrophic damage if they were not accompanied by an unusually strong liquefaction of soils in an area of hundreds of square kilometers. This is the conclusion of a team of researchers at Oregon State University, who worked on the site of earthquakes.
Due to the fact that the earth has suddenly become unstable, many buildings moved from their seats, tilt and partially left in the soil, although they are not directly earthquake damaged. Shifts diluted soil destroyed not only buildings, but also water, sewer and gas pipelines in the number of settlements. The scale of this phenomenon in the Japanese subduction zone — a place where one block crust dives under another — surprise experienced specialists who study the consequences of the most devastating natural disasters.
"We used to see local examples of soil liquefaction, but in Japan their area and the amount of damage caused by an unusually large", — said Scott Ashford (Scott Ashford), professor of geotechnical engineering at Oregon State University and a member of the research team.
Soil liquefaction is accompanied almost every major earthquake. It occurs when the ground by vibration loses strength and behaves as a liquid or shaken loose material. Especially for soils with a high content of sand and gravel. They begin to "swim", increasing destruction.
"Due to the fact that the earthquake lasted about five minutes, the buildings that have survived the first 30 seconds, then plunge and leaned back in a few minutes, until the shaking continued, — says Ashford. — And it was clear that the young soils, especially in the areas recently covered with earth, were much more vulnerable. " Recall that in Japan, there is a practice to expand existing island and pour new ones to increase habitable territory.
The buildings, which are built on fragile soils, not only tend to fall or give the bank, they also slip into the lowlands, if any slope, for example, in the direction of a nearby river. Analysis of the Japanese earthquake, the researchers say, will help to better understand this phenomenon, in order to reduce risks during construction in earthquake zones.