Cascadia's Fault - Jerry Thompson [85]
The images mesmerized everyone in the room. There in full 3D relief stood Okushiri Island as the leading wave approached the beach. Instead of black night we could see it all in perfect daylight detail, a view from space that could zoom right down to sea level and hover at any angle to see what the wave would do from every conceivable perspective. Titov and Moore had taken data points from the Japanese scientists, entered those numbers into the computer and rolled the timeline backward to the beginning.
Knowing how the wave ended—how high it pegged the needles on tide gauges, how far up the various beaches it ran—they reverseengineered the event all the way back to flat water the moment before the Hokkaido quake and could play it again and again by clicking a mouse. This was more than just high-quality 3D animation—they had converted raw data into computer code to recreate the wave, then converted it again to graphical animation files that let them “fly” through the air above Okushiri and look at every hair on this monster’s head.
When they hit playback, they ran the event in slow motion to examine exactly how the waves changed shape, size, and direction as they rolled uphill from deep water, scraping across the rough terrain of the foreshore, the fronts of the waves slowing down because of friction and a heavy load of silt and the trailing edges still moving fast, rising high and crashing hard at last against dry land. It was amazing to see, especially when I reminded myself that this was based on real data from the real wave, not the fantasy of some Hollywood special-effects studio.
“What I like about it,” said Chris Moore, his hand on the mouse, “is the aerial photograph pasted over so that you can actually see exactly where the town is situated with respect to the wave.” It looked like Google Earth come to life in 3D. “This is an airstrip.” Moore nodded at the screen. “Each of these little dots is a rooftop—in reds, whites, and blues. So you can sort of see approximately how large the wave is.”
Moore pointed to the small peninsula that was about to be overtopped by the tsunami. In the animation a train of three waves approached the beach. “Here it’s shallow,” he said, hovering the cursor near the southernmost tip of land. “It’s deeper water off of here.” He moved the cursor farther off the beach. “And this wave front, as it animates through, tends to bend around the headland because the wave is slower in shallower water and faster in deeper water. So it bends right around there.”
The computer made it perfectly obvious why the waves would slow and turn as they did. “And then this group of waves here ...” Moore zoomed closer to a second point of land, the graphics revealing a steep cliff overlooking a small bay. “It also shows reflection off of that headland.” The incoming waves bounced off the wall of rocks and ricocheted back across the bay to hit what had been a sheltered cove on the lee side of the incoming tsunami’s path.
Suddenly Titov tapped the space bar to pause the wave. “See this kind of fissure when the wave withdrew from the coast and formed a hydraulic shock?” He pointed to a frozen wall of water standing just beyond a beach that had been completely drained of its surf right down to bare sand. “That’s the first time—this animation—is the first time I saw anything like that. And if there was no animation, we probably wouldn’t have picked it up.”
“Yeah,” Moore enthused, “let’s just single-step through it and see how it goes.” He rewound the wave ever so slightly and played it back frame by frame. “So right about here is where it’s forming,” he mumbled as the leading wave fell back down the beach, taking all the water with it.