Cascadia's Fault - Jerry Thompson [86]
Because the Okushiri waves struck in darkness there were few eyewitnesses as the tsunami approached. This animation was apparently the only way to know how the shape of the local sea floor had affected the incoming water. Case histories elsewhere explained and verified what the computer was showing.
“There are eyewitness accounts from the Chile event that sounded really weird,” Titov offered. “They were saying the second wave was sitting outside—offshore—waiting and gaining force ... And that’s what it was,” he pointed again at the screen. “That was this hydraulic trough—not propagating any more, just sitting there ... The second wave competing with the retreat from the first wave, creating a standing wave pattern.”
The point of showing us the playback of the Okushiri tsunami was to illustrate how far wave modeling had come by 1993. “This was in fact the first wave that we’ve tested our model against in terms of real event simulations,” said Titov. “It was the most studied and the largest event before Sumatra, really.” The model was still a prototype, however, and much work remained to be done. New research programs were launched to figure out how to simulate the small-scale details of coastal terrain and more complex problems such as the way waves break, how they transport sediment and debris, and how a wall of moving water interacts with solid objects on land.
The lessons of Okushiri were encouraging for Vasily Titov and his colleagues. “You really wonder what’s behind it,” he mused, “what kind of wonders mathematics can do. Writing equations, putting it in the computer, plotting it. And then you see the wave evolving just like you saw on TV ... Things that I saw when I did the animation of the tsunami in Japan—we would never see it just looking at the formulas ... It’s really the power of mathematics working for you.”
As the research began to accelerate, so did the ramifications of ignoring or neglecting Cascadia as a major public-safety issue. Within months of the Okushiri disaster in Japan, another scare in the Pacific Northwest and sobering new science from Canada would force politicians to take the initial concrete steps toward a viable coastal warning system. Festering debates and old controversies would be put to rest as the scale and potential of Cascadia’s fault became glaringly undeniable.
CHAPTER 15
Defining the Zone: Hot Rocks and High Water
Decades of terror, or the magnitude 9 scenario—which will it be for Cascadia’s fault? Apparently Gary Carver and Brian Atwater took enough flak from some of their colleagues for using such terms to describe the possible fate of the Pacific Northwest that they decided to tone down the language in subsequent talks. They started referring somewhat in jest to the biggest, full-margin rupture—the magnitude 9 scenario—as a “dinner sausage” earthquake and the series of slightly smaller magnitude 8s as being “breakfast links.” The question of which scenario was more likely to happen remained unanswered and vigorously debated.
Early in the new year of 1994, in the AGU’s Journal of Geophysical Research, a team of scientists at the Geological Survey of Canada took a stab at defining how much of the subduction zone was locked together and which parts might be moving along smoothly. Presumably, if you knew how much of the zone was locked—if there were some way to measure and define it—you might be able to estimate the size of the rupture that would be generated when the thing finally came unstuck. Drawing a line around the “seismogenic zone” would tell emergency planners how close the quake’s epicenter was going to be to major urban areas like Vancouver, Victoria, Seattle, and Portland.
The Canadian team gathered and distilled all the latest reports from both sides of the international border that showed how much the outer coast was being lifted up, dropped down, or squeezed together. Then they plotted the boundaries of each type of data to show exactly