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First Tsunami Safe Haven Building in the United States

Ocosta School Construction

The City of Westport stands sentry at the tip of a narrow peninsula between the expanse of the Pacific Ocean and the protection of Grays Harbor. The Cascadia Subduction Zone, a 700-mile-long earthquake fault zone, lurks approximately 90 miles off the shore. Experts predict this submerged fault zone will release a magnitude-9.0 earthquake and unleash a tsunami that will hit the coasts of British Columbia, Washington, Oregon, and California. The last such “megaquake” struck just over 300 years ago.

As was recently seen in Chile, Indonesia, and Japan, tsunamis ravage low-lying areas such as Westport. There, it is expected that a tsunami from a Cascadia Subduction Zone megaquake could reach the coast in as little as 20 minutes. However, evacuation of Westport and neighboring Ocosta Elementary, Junior and Senior High Schools could take nearly double that time. Therefore, in 2013 residents of the Ocosta School District approved re-construction of an aging elementary school that will include the nation’s first tsunami “refuge” structure.

Construction of the school started in November 2014. The school’s gym has been designed to withstand the impact of a tsunami and the debris it carries, while sheltering nearly 1,000 people on its roof. The roof is 30 feet above the ground (nearly 55 feet above sea level) to keep people dry and safe. The gym’s roof is supported by heavily reinforced concrete towers in each corner that are designed to remain intact during shaking from the initial megaquake, associated aftershocks, and the resulting tsunami surges.

Because of the potential for over 10 feet of scour (soil erosion adjacent to the building) caused by tsunami surges and liquefaction of the native sandy soils, the gymnasium is supported on nearly 50-foot deep piles. The remainder of the school is supported on shorter piles designed to withstand earthquake shaking and liquefaction, but not necessarily tsunami surge forces.

Links below lead to more information on the Ocosta building and general tsunami research. Note that the maps on the last link (Project Safe Haven) illustrate how impossible it would be to escape a tsunami in the Ocosta area.

Rooftop Refuge Washington Disaster News, Washington Military Department Emergency Management Division
Grays Harbor County school to build first U.S. vertical-tsunami refuge Seattle Times
First tsunami-proof building to be built in Westport Komo News
Rising above the risk: America’s first tsunami refuge the Geological Society of America
Project Safe Haven: Tsunami Vertical Evacuation in Washington State

Geotechnical Lessons from the Tohoku Earthquake

Japan landslide area

Rockslide (background) and flood protection (foreground) in Ishinomaki City, Japan (Photo: Dave Swanson, Reid Middleton)

The magnitude 7.3 earthquake that struck Japan six days ago is a reminder of the more devastating magnitude 9.0 earthquake that struck March 11, 2011. In an earlier post we mentioned a reconnaissance team that traveled to Miyagi Prefecture in Japan in May 2011 after the earthquake and tsunami.

In the landslide area photo above from 2011, the light colored rock slope failed even with reinforcement that protected the slope to the left. The entire land area settled, which allowed Tsunami and high tide water access to the shoreline. Fortunately, in this area the Tsunami water was not as high as other areas, so the buildings weren’t washed away. Blue tarp temporarily protects the river bank from overtopping at high tide.

Doug Lindquist of Hart Crowser had these observations about the geotechnical damage:
Damage generally happened in known geologic hazard areas (tsunami zones, areas near past landslides, liquefiable areas, and reclaimed land).
• Liquefaction damage was extensive even 150 kilometers away from the fault rupture. (Seattle is about 100 kilometers from the Cascadia Subduction Zone.)
• Ground improvement measures are effective.
• Engineering methods can reasonably estimate the liquefaction hazard.
• Newer structures performed well when designed considering known geologic hazards.

As the reconnaissance team report reminds us, a similar earthquake will happen along the Cascadia Subduction Zone, off the coastline from northern California to British Columbia. The impacts of this event on our communities and industry will depend on the actions we take now to prepare for it. The lessons learned from Japan can be applied in our own communities.

For more details on the reconnaissance team’s findings, along with some fascinating photographs, see the report here.