When a severe earthquake strikes a distant community, Scott Ashford gets on a plane. He travels light but packs enough to be self-sufficient. He is, after all, going into a disaster zone where emergency personnel don’t need another mouth to feed. The head of the Oregon State University School of Civil and Construction Engineering is a member of the Geotechnical Extreme Events Reconnaissance, or GEER advance team, supported by the National Science Foundation.
“Our mission is to get word out to the scientific community about what’s happened on the ground,” he says. As a geotechnical engineer, he is particularly interested in soil changes following an earthquake. His findings raise questions about the adequacy of building standards in the United States and abroad.
In the past year, Ashford has inspected the aftermaths of quakes in Chile, New Zealand and Japan. The work demands humility. Out of respect for people who lived through terrifying events, he warns younger colleagues to avoid expressing excitement over significant findings. “We’re amongst people who have had their lives ruined and are in upheaval,” he says. “Even though it’s exciting to see the things we’ve been doing research on in action, you can’t show any of that. It’s an emotional rollercoaster.”
And it demands a keen eye. Careful measurements of structural damage, landslides, soil liquefaction and shifted fault lines can help engineers to design more resilient structures. The whole point is to save lives and reduce the damage that will occur when the next Big One hits, a goal shared by more than a dozen of Ashford’s colleagues in engineering and geophysical sciences at OSU.
Buildings on Quicksand
Ashford has seen buildings torn in half as if they were made of LEGOs®, bridges demolished or jackknifed on their foundations and utility pipes squeezed out of the ground. One his team’s most significant findings came from the March 11 subduction zone earthquake in Japan, which caused soil liquefaction — wet sands, gravels, silts and fill materials turned into soup as they shake, with all the load-bearing capacity of quicksand — that surprised researchers with its geographic extent and widespread severity.
In order to gather evidence of this phenomenon, Ashford and his team looked for sand boils (small sand volcanoes) and lateral spreads — that is, shallow landslides triggered by liquefaction. Although they arrived only two weeks after the initial quake, cleanup was already taking place, erasing evidence in some locations, which is why GEER teams are sent in quickly after a major event.
“The data are very perishable,” he says. But the more evidence they can gather about how soil has altered during an earthquake, the better engineers will be at predicting the outcomes of future quakes.
“We’ve seen localized examples of soil liquefaction as extreme as this before, but the distance and extent of damage in Japan were unusually severe. Entire structures were tilted and sinking into the sediments, even while they remained intact. The shifts in soil destroyed water, sewer and gas pipelines, crippling the utilities and infrastructure these communities need to function. We saw some places that sank as much as four feet.”
Parts of the West Coast of the United States are vulnerable to the phenomenon. They include Portland, parts of the Willamette Valley and other areas of Oregon, Washington and California. Around San Francisco Bay, for example, the U.S. Geological Survey categorizes most of the low-lying lands as having moderate to very high susceptibility to liquefaction.
Some degree of soil liquefaction is common in almost any major earthquake. It can allow structures to shift or sink and significantly magnify the structural damage produced by the shaking itself.
New Construction Standards
But most earthquakes are much shorter than the event in Japan, Ashford adds. The length of the Japanese earthquake, as much as five minutes, may force researchers to reconsider the extent of liquefaction damage possible in situations such as this.
OSU’s Scott Ashford and Pat Corcoran discuss earthquake preparedness
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“With such a long-lasting earthquake, we saw how structures that might have been OK after 30 seconds just continued to sink and tilt as the shaking continued for several more minutes,” he says. “And it was clear that younger sediments, and especially areas built on recently filled ground, are much more vulnerable.”
The data provided by analyzing the Japanese earthquake should make it possible to improve the understanding of this soil phenomenon and better prepare for it in the future. Ashford says 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 adds. “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, don’t happen everywhere, even in other regions such as Southern California that face seismic risks. But an event almost exactly like that 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.
West Coast on Edge
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. These “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 says. “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. But another reasonable goal is to at least 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.
The 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 GEER 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.
Collaboration Is Key
The GEER team always pairs up with researchers from the country where they’re working. This not only helps them with cultural and language issues, but allows them to be guided by the hosting country’s scientists as to where it’s appropriate, and safe, to conduct their research. It is also a great way to foster international collaboration.
“You can develop strong personal bonds with someone spending a week together in the car doing an earthquake reconnaissance,” Ashford says. And it is those personal relationships that make the follow-up research collaboration possible.
During his trip to Japan, Ashford had to balance his own emotional reactions to the devastation. A colleague there showed him a video that hadn’t been aired on television. It was a shot of the water level rising on the Japanese coast as witnesses gathered on the shore, unaware of the danger. In a flash, the tsunami waves hit the coast, obliterating everything, and everyone, standing on the shore.
“We both teared up,” Ashford says. “It was very emotional to see that.”