Cascadia's Fault - Jerry Thompson [4]
Cascadia is virtually identical to the offshore fault that devastated Sumatra—almost the same length, the same width, and with the same tectonic forces at work. This fault can and will generate the same kind of earthquake we saw off Sumatra: magnitude 9 or higher. It will send crippling shockwaves across a far wider area than all the California quakes you’ve ever heard about. Cascadia’s fault will slam five cities at once: Vancouver, Victoria, Seattle, Portland, and Sacramento. It will cause physical damage as far south as San Francisco.
Cascadia’s fault will cripple or destroy dozens of smaller towns and coastal villages from Tofino and Ucluelet on Vancouver Island to Crescent City and Eureka in northern California. None of these cities and towns will be able to call their neighbors for help because they will all be on their knees in rubble at exactly the same moment. California, with all its hard-earned earthquake experience, won’t be able to offer much assistance to Oregon or Washington because it will have too many emergencies of its own to cope with. There will be no cavalry racing over the hill to save the day, no government white knights to bail anybody out. It’ll be every man, woman, and child for themselves in three American states and a Canadian province.
The San Andreas has and will again cause terrible, destructive earthquakes, probably sooner rather than later, but the offshore temblor from Cascadia will be on a much larger scale. The San Andreas will wreck a major urban area—perhaps San Francisco or Los Angeles—but probably not both at the same time. Cascadia’s fault will hammer an entire region of the planet, just as the Sumatra disaster did.
I know it’s not scientific, but just for the sake of comparison, I fashioned a small ruler out of a piece of paper and held it up against a globe. I put a pencil mark midway up Vancouver Island and another at Eureka, California, creating a paper proxy for Cascadia’s fault. Then I moved it to the east coast of North America. An eight-hundred-mile (1,300 km) tectonic crack like this—if it started in New York—would run down through Philadelphia, Baltimore, and Washington to about Charleston, South Carolina. The same fracture, if it started in Detroit, would run past Niagara Falls, through Toronto and Montreal to roughly Quebec City. Or from London through Paris to Nice, France. Or from Lisbon across Portugal to Barcelona. Or from Berlin to Milan.
There’s evidence to suggest that Cascadia’s fault would not act alone—that an earthquake along this subduction zone could transfer enough stress to trigger the San Andreas at the point where the two faults connect, near Cape Mendocino, about three hundred miles (480 km) north of San Francisco. Mud-core sampling of undersea landslides off the Pacific Northwest and California coasts has revealed a fairly close time correlation between ruptures on the two fault systems for many of the largest quakes in the past.
It could happen like this: a magnitude 9 rupture on Cascadia causes an unprecedented natural disaster that affects the entire Pacific Rim. It also sends a strong jolt into the neighboring San Andreas system, which is already nearing its own failure along the Hayward fault in Oakland. Ten or twenty years later, while Americans and Canadians are still rebuilding from the recent Cascadia event, the San Andreas rips loose and California is back on its knees again.
That’s not all. Cascadia will also slam the beaches