Tsunami Safe-Haven Building, Ocosta School

Ocosta School District
Westport, Washington

Ocosta School

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.

In a low-lying area such as Westport, 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, residents of the Ocosta School District approved re-construction of an aging elementary school that will include the nation’s first tsunami “refuge” structure.

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.