Cascadia's Fault - Jerry Thompson [137]
In the small town of Taiki, the Nishiki Tower was custom built to survive the effects of the expected Tokai earthquake. It was also hydrodynamically designed to withstand the forces of fast-moving water. With rounded, conical walls and a spiral stairway to the top, it has shelter rooms and emergency supplies on the upper floors. The thing is—it looks odd—like a tall, white lighthouse in the middle of town, completely out of place. And that causes out-of-town visitors to stop and ask questions.
“If I see such a tower,” Harry Yeh speculated, putting himself in a visitor’s shoes, “I’m gonna ask the people, ‘What is this?’ So everybody will know that’s a tsunami shelter.” He smiled. In essence, looking odd or out of place could help a tsunami shelter save lives. “I think this is a very important component of the design,” he said. In the meantime he and a study team continued to work on a new set of building code guidelines for vertical evacuation shelters.
Among the engineering challenges, according to a report issued at the end of the first phase of the study, was that designing a building to withstand a seismic shock is in some ways the opposite of what you’d need to survive a tsunami. To ride out an earthquake, a building needs “flexibility, ductility and redundancy.” To outlast a tsunami it needs “considerable strength and rigidity, particularly at the lower levels.” But Harry Yeh insisted these requirements “need not be contradictory” and stressed that both had to be taken into account.
The foundations of a tsunami shelter would have to withstand not just the violent shaking but the soil liquefaction that often accompanies a quake. They must be deep enough below unstable soil to be anchored on firm bedrock. The building itself would have to provide enough floor space for evacuees and be tall enough to stand above the largest expected wave. The walls would have to be strong enough to withstand the battering-ram effect of water-borne missiles (floating cars, logs, lumber, and other debris). It would have to be fire resistant since quakes and tsunamis always cause numerous fires to break out. The final design requirement would be resistance to scour. The foundations of a shelter would have to withstand the rapid rise and fall of fast-moving water that would “loosen the soil skeleton” around the building, possibly causing collapse.
While the challenge sounds daunting, the report underlines the obvious concern that vertical evacuation may be “the only choice for human survival” in many coastal communities. Because of the engineering complexity shelter designs will probably have to be done on a case-by-case basis. Every beach and the bottom of every bay is a little bit different.
CHAPTER 23
Watching It Happen, Wishing It Wouldn’t
Harry Yeh, Patrick Corcoran, and Chris Goldfinger met on the campus of Oregon State University in Corvallis for one of the most riveting demonstrations of the power of moving water I’d ever seen. Behind the blue-gray corrugated metal walls of a hangarlike building that looked big enough to hide a blimp, in a wave research basin half the size of a football field, researchers led by civil engineer Dan Cox had built a scale model of the town of Seaside, Oregon. The object of the exercise was to test the effects of a tsunami from Cascadia’s fault on a detailed physical replica of Seaside’s downtown core. Computer models had already predicted what would happen, but how would real water behave compared to a hypothetical digital clone?
Graduate students and technicians from OSU had spent months building plywood surrogates for each of the main beachfront hotels, commercial buildings, parkades, and homes in the downtown area. They built an inclined platform and poured a concrete floor at exactly the same angle as the sea floor and beach. They constructed a breakwater exactly like