Cascadia's Fault - Jerry Thompson [56]
Adams latched on to this as a possible explanation for the eastward tilting and thought he’d made a pretty convincing case. He was not completely successful, however, in exorcising the demon of aseismic subduction. At the request of his more senior coauthor, Robert Reilinger, he wrote a concluding paragraph that equivocated enough to dull the edge considerably. Taken as a whole, the tilting data and the lack of large quakes “suggests that subduction is occurring aseismically, although alternative interpretations are possible,” they wrote cautiously. Thinking about it more than thirty years later, Adams had to laugh. “That phrase was largely put in to—shall we say—to take the controversy out of the paper, to make sure it got through the peer-review process.”
But Adams was already hard at work on another study that would pull fewer punches. He was like a dog with a bone. He knew the mountains were tilting, he knew Puget Sound was getting squeezed, and he intended to follow up on those beaches that had been shoved up into marine terraces along the Oregon coast. He knew from his New Zealand studies that it took hundreds of years to build up enough strain for a giant subduction quake. And he knew about those turbidite mud cores from offshore landslides that also were roughly five hundred years apart. Were the deep-sea landslides physical proof of Cascadia’s violent past? He was determined to find out.
CHAPTER 10
The Whoops Factor: Cascadia’s True Nature Revealed
While John Adams watched the Coast Range tilt and Jim Savage tracked the squeezing together of mountain peaks in Puget Sound, Mike Schmidt was learning about a new technology that could make the measurements far more precise. He would eventually join a team of researchers on Vancouver Island, where the distance between several mountain peaks was being resurveyed to find out whether continental drift was shoving them closer together as well.
My first impression of Schmidt was that he’d rather climb a big rock pile than stand there and look at it. He’s a bearded bear of a guy who seems to have chosen the right career. In 1992 he led a team of Canadian scientists to the top of Mount Logan, Canada’s highest peak and its fastest rising mountain. Fast in geologic terms, it grows by several fractions of an inch each year.
As a mountain climber, geophysicist, and surveying engineer, Schmidt wanted to establish new geodetic markers near the summit and try out some brand new and allegedly portable GPS technology, which was still in the experimental stage at the time, to trace the peak’s constant movement. Logan, which occupies a big chunk of the southwestern corner of the Yukon, is poking up and creeping horizontally for the same reason that mountains in Puget Sound near Seattle are getting squeezed together. In the case of Logan, the floor of the Pacific Ocean is jamming itself underneath North America from the Gulf of Alaska.
This is the same tectonic force that caused the 1964 Alaska earthquake. The Pacific plate is thrusting the entire St. Elias Range a tiny bit higher and shoving it slowly inland at the same time. Because 1992 was Canada’s 125th birthday and the 150th anniversary of the Geological Survey, Schmidt came up with the idea of putting together an expedition to climb the mountain and settle a long-standing debate about how high Mount Logan really was. With sponsorship from the Royal Canadian Geographical Society, he and his team did