The Zone is a 700-mile-long fault on the US West Coast where the Juan de Fuca Plate is pushed under the North American Plate. It has the potential to generate magnitude nine earthquakes.
‘It used to be thought that Cascadia was not an active fault,’ said Tim Walsh, chief hazard geologist at the Department for Natural Resources. ‘Not only has Cascadia [now] been found to be an active fault, it has a ten per cent chance that it will cause an earthquake in the next 50 years.’
In order to mitigate the threat, Walsh developed the first tsunami shelter in the US. The modified school gym can shelter 1,000 people within a 20-minute walking distance, and was chosen after using tsunami modelling to determine the best location. Called GeoClaw, the model allowed oceanographers, engineers and geographers involved in the project to work out where additional risks, such as landslides, would occur. It also allowed the project to determine how much pressure the shelter would have to withstand.
The shelter is to be built on a dune ridge, which will leave the roof standing 55 feet above sea level. Reinforced concrete cores at the building’s corners and stairways are designed to withstand the earthquake and any following storm surge. At the moment, the Washington coastline has few buildings taller than three stories, leaving many vulnerable to tsunami risks, added Walsh.