The coastline itself must have plunged into the ocean. Sea levels can’t rise six or more feet in a year. Something extraordinary happened that year. According to tree-ring dating, every one of those forests was buried in 1700. Atwater’s first clue was the “ghost forests” along the Oregon and Washington coasts, drowned by seawater, covered by sand and landslide debris, and then exposed by beach erosion. Oregon had recorded no earthquakes since American pioneers colonized the territory in the nineteenth century, and the native population had no written records, but the earth itself keeps copious records of geologic events, once one knows where to look. University of Washington geologist Brian Atwater proved them wrong in the late 1980s. Geologists knew about the Cascadia Subduction Zone, but they thought that the Pacific and Juan de Fuca Plates weren’t locked-that the subduction was smooth, as if the continent were greased with lubricant. Seismic hazard maps shaded California red and Oregon green. Everyone, including scientists, thought us immune.
When I was a kid, growing up in the mid-Willamette Valley in Oregon, earthquakes were California’s problem. We didn’t even know a megaquake was coming until recently. Shockwaves will unleash more destructive force against the United States and Canada than anything short of nuclear war, a giant asteroid strike, or a civilization-threatening super-volcano. Roughly 100 miles off the West Coast, running from Mendocino, California, to Canada’s Vancouver Island, lurks the Cascadia Subduction Zone, where the Juan de Fuca Plate is sliding beneath the North American Plate, creating the conditions for a megathrust quake 30 times stronger than the worst-case scenario along the notorious San Andreas, and 1,000 times stronger than the earthquake that killed 100,000 Haitians in 2010. The Big One, though, is a mere mini-me compared with the cataclysm forming beneath the Pacific Northwest. Americans have long dreaded the “ Big One,” a magnitude 8.0 earthquake along California’s San Andreas Fault that could one day kill thousands of people and cause billions of dollars in damage.
0 kommentar(er)
