Cascadia's Fault - Jerry Thompson [108]
Goldfinger can still recall the doubt and disbelief that flashed through the corridors of the marine geology department when the first John Adams paper appeared in the scientific literature saying, in essence, that Griggs and Kulm should have ignored the potential skeptics. Without going to sea, without collecting a single new sample himself, Adams, the outsider, this transplanted New Zealander who had moved to Canada via Cornell University, wrote a paper based on the Griggs and Kulm cores and concluded that seismic jolts were the best—indeed the only logical—explanation for the thirteen turbidites.
It must have seemed as though a foreign spy had raided the OSU lab and stolen the thunder of the home team’s original discovery. As it turned out, not a bit of skulduggery was involved. Adams simply wrote to OSU officials asking permission to look at some of the core logs that had been sitting in storage since 1968. Picking up the storyline more than three decades later, Chris Goldfinger told his colleagues aboard the Roger Revelle off the coast of Sumatra how an amazing feat of deductive reasoning had come about.
“He saw the same thing [that Griggs and Kulm had seen], that there were thirteen turbidites above the Mazama ash. So he tried to come up with a method to prove or test the origin of these things. And what he did was this: he noticed that there’s a confluence of two channel systems right through here.”
Goldfinger pointed to the map beamed from his computer via an overhead projector to a screen at the front of the ship’s lounge. “Well, it turns out that all of these cores have thirteen turbidites.” He pointed to sampling sites on both main channel systems. “So here’s his little test, right here. He said, ‘Well, okay—if you have two channels or two canyon systems, 200 kilometers [125 miles] apart, and one has thirteen turbidites and the other has thirteen turbidites—how could you possibly pass the confluence and go downstream and not have twenty-six turbidites?”
Goldfinger scanned the faces around the room to see fascinated smiles and raised eyebrows. “You should have twenty-six turbidites here, right?” Landslides send thirteen turbid currents of sand sloshing down two channels that run together, so there ought to be a total of twenty-six turbidite layers in the mud downstream from the confluence.
“And there are only two ways you could not have twenty-six,” he continued. “One is that it just coincidentally dropped out thirteen of them [for unknown reasons, thirteen of the landslides didn’t make it past the confluence], which didn’t seem very likely. And the other way is that they arrived at the confluence at exactly the same time, plus or minus about five minutes—and merged.” In other words, if a big quake triggered a landslide at the same moment at the head of each of the major canyons along hundreds of miles of the continental shelf, then all the mud flows would cascade downhill synchronously and would arrive at the downstream confluence where all the offshore sea channels meet—at the same moment.
Below the confluence there would be a single, merged turbidity flow. No matter how many small tributaries fed into the main channel from the steep slopes above, the total number of turbidites below the confluence would always be the same: one for each coastwide landslide. The only reasonable explanation for so many landslides happening synchronously along so many miles of coastline was large subduction earthquakes.
“And that’s what John argued,” said Goldfinger. And then he paid one of the highest compliments one scientist can offer another. “This was done purely with thinking power. And that’s out of fashion these days.” The praise seems all the more significant given