Cascadia's Fault - Jerry Thompson [111]
Essentially they had encountered the same problem with radiocarbon dating that Brian Atwater did: there was very little biotic material to work with in deep-sea mud, and it had a way of getting moved around by burrowing sea creatures and sloshed out of the tops of the piston cores as they were wrangled onto ship’s decks in heaving ocean swells. Unlike Atwater they could not rely on a ghost forest of ancient cedars conveniently nearby; nor could they use tree rings cored from perfectly preserved roots to help nail down the turbidite dates by other means.
They did, however, feel confident the wiggle-matching technique borrowed from their oilfield colleagues would eventually overcome these problems to help establish a solid and convincing long-term history for Cascadia. By December 2004 the clustering story had become more refined. Their turbidite studies had been updated, peer reviewed, and republished in several different science journals with enough new details that the media relations department at Oregon State decided to issue a news release. A draft prepared just before Christmas was set aside to be polished and sent out after the holidays.
Then, when no one was looking, another subduction zone in the Ring of Fire ripped apart, and the entire planet got knocked for a loop by a temblor so big it made the earth wobble slightly on its axis. The great Sumatra quake and tsunami of 2004 happened the day after Christmas and all eyes shifted instantly to the Indian Ocean. So it’s unlikely that any more than a few diligent local reporters paid much attention to the OSU release issued on New Year’s Eve. For those who bothered to read it, the release provided the latest chronology of clustered quakes on Cascadia’s fault, a historical record with “two distinct implications—one that’s good, the other not.”
Looking at the expanded pattern of turbidite beds off the coast of the Pacific Northwest, Goldfinger and Nelson concluded that the Cascadia Subduction Zone had experienced “a cluster” of four massive ruptures during the past 1,600 years. If the trend continued—if the pattern repeated—“this cluster could be over and the zone may already have entered a long quiet period of 500 to 1,000 years, which appears to be common following a cluster of earthquake events,” noted the OSU release. That was the good news.
The alternative scenario was that the current cluster might still have one or more jolts left in it. The release pointed out that some clusters had up to five events and that within a cluster the average interval between earthquakes was three hundred years. By now most aware residents of the Pacific Northwest had heard the story that Cascadia’s last megathrust shockwave was January 26, 1700, and therefore the next event might well be imminent.
“The Cascadia Subduction Zone has the longest recorded data about its earthquakes of any major fault in the world,” wrote Goldfinger in the OSU release, putting his new ten-thousand-year turbidite timeline front and center. “So we know quite a bit about the periodicity of the fault zone and what to expect. But the key point we don’t know is whether the current cluster of earthquake activity is over yet.”
By December 30, 2004, when the OSU release went out to the media, the total number of Cascadia earthquakes identified in the turbidite cores had advanced from eighteen to twenty-one, at least seventeen of which had ruptured the entire length of the plate boundary from Vancouver Island to Cape Mendocino, causing magnitude 9 shockwaves and major tsunamis almost identical to the frightful scenario the whole world was watching hour after hour as the Boxing Day tragedy played out across the Indian Ocean. What we were seeing on television had happened here too—at least seventeen times.
When Goldfinger went to sea off the coast of Sumatra in the summer of 2007, the Cascadia turbidite data had been updated and refined yet again. The temblor count had gone up again as well. When I met