How it Could Happen

The Cascadia Fault, which stretches from northern California to Vancouver, has caused 40 earthquakes over the past 10,000 years, with big tumblers recurring as often as every 250. The fault is currently “locked,” meaning the plates are jammed together and building up destructive energy. The last big quake, powerful enough to send a tsunami to Japan and possibly trigger a mudslide that temporarily dammed the Columbia River, was in 1700. “For the northern margin [of the fault], the odds of a quake are 10 to 15 percent in the next 50 years,” says Chris Goldfinger, director of Oregon State University’s Active Tectonics and Seafloor Mapping Laboratory. “In southern Cascadia the odds are much higher.” If the fault goes, the first wave could hit in less than 15 minutes.