Much of earthquake damage in Japan caused by "liquefaction"

future. Ashford said it was critical for the team to collect the information quickly, before damage was removed in the recovery efforts.

“There’s no doubt that we’ll learn things from what happened in Japan that will help us to mitigate risks in other similar events,” Ashford said. “Future construction in some places may make more use of techniques known to reduce liquefaction, such as better compaction to make soils dense, or use of reinforcing stone columns.”

The massive subduction zone earthquakes capable of this type of shaking, which are the most powerful in the world, do not happen everywhere, even in other regions such as Southern California that face seismic risks. An event almost exactly like that, however, is expected in the Pacific Northwest from the Cascadia Subduction Zone, and the new findings make it clear that liquefaction will be a critical issue there.

Many parts of that region, from northern California to British Columbia, have younger soils vulnerable to liquefaction - on the coast, near river deposits or in areas with filled ground. The “young” sediments, in geologic terms, may be those deposited within the past 10,000 years or more. In Oregon, for instance, that describes much of downtown Portland, the Portland International Airport, nearby industrial facilities and other cities and parts of the Willamette Valley.

Anything near a river and old flood plains is a suspect, and the Oregon Department of Transportation has already concluded that 1,100 bridges in the state are at risk from an earthquake on the Cascadia Subduction Zone. Fewer than 15 percent of them have been retrofitted to prevent collapse.

“Buildings that are built on soils vulnerable to liquefaction not only tend to sink or tilt during an earthquake, but slide downhill if there’s any slope, like towards a nearby river,” Ashford said. “This is called lateral spreading. In Portland we might expect this sideways sliding of more than four feet in some cases, more than enough to tear apart buildings and buried pipelines.”

Some damage may be reduced or prevented by different construction techniques or retrofitting, Ashford said. Another reasonable goal is at least to anticipate the damage — to know what will probably be destroyed, make contingency plans for what will be needed to implement repairs, and design ways to help protect and care for residents until services can be restored.

Small armies of utility crews are already at work in Japan on such tasks, Ashford said. There have been estimates of $300 billion in damage.

The recent survey in Japan identified areas as far away as Tokyo Bay that had liquefaction-induced ground failures. The magnitude of settlement and tilt was “larger than previously observed for such light structures,” the researchers wrote in their report.

Impacts and deformation were erratic, often varying significantly from one street to the next. Port facilities along the coast faced major liquefaction damage. Strong Japanese construction standards helped prevent many buildings from collapse – even as they tilted and sank into the ground.