Cascadia’s Fault: An ExcerptBy Jerry Thompson
June 04, 2011
On Christmas Eve 2004 my wife, Bette, and I were in a hotel bar in San Francisco dreaming up plot points for a film we’d like to shoot some day when a woman arrived from the airport with breathless news. The bartender clicked his remote and It’s a Wonderful Life vanished, Jimmy Stewart’s smiling face wiped off the screen by a mountain of angry seawater. I can still see those endlessly repeated loops of amateur video shot from the balconies of beachfront resorts in Sumatra and Thailand, relayed by satellite to every TV receiver on the planet.
The first horrifying, mesmerizing wave crashed against a seawall, jetting skyward in salty white torrents, tearing through a fringe of palm trees like a monsoon river, across a hotel pool deck and a manicured square of green lawn. The darkening surge roared uphill through narrow, cluttered streets choked with tourist luggage, broken timbers, small motorcycles with their riders struggling to stay vertical, cargo vans overturned and bulldozed by white froth into market stalls. A transit bus floating on its side began to sink as desperate passengers jumped from the slippery roof.
It’s impossible to forget the images, those flailing human bodies—especially one unfortunate older man clinging to the outside railing of a rapidly filling parkade. Exhausted and in shock, he finally let go. We watched as he sank into the muddy torrent and was swept away.
More than 230,000 people in fourteen countries around the Indian Ocean died or disappeared, many of them before our eyes, and there was nothing any of us could do. Everything not nailed to the ground was torn loose and carried off by the roaring water. And there was more to come. Even after the first water had cut a swath nearly a mile inland and then sucked itself halfway out to sea again, full of death and floating debris, people standing among the palms were so stunned by the spectacle they waited too long to outrun the next wave.
Most victims, including those who’d lived their entire lives along the beach—even fishermen who knew the sea quite well—had no idea these giant ripples would come ashore again and again. In Phuket, Thailand, some of the swells were sixty-five feet high. Closer to the earthquake zone, in Aceh province on the northern end of the island of Sumatra, the mountain of water topped more than a hundred feet.
Until that moment, only a handful of people in the world had ever experienced a tsunami. Fewer still had any concept of what causes these so-called tidal waves. The magnitude 9.2 earthquake, generated by the movement of two tectonic plates along an almost nine-hundred mile (1,400 km) undersea fault called the Sunda Trench, was never more than a footnote in the nonstop cycle of dismal news. The last time anything this big had happened in the Indian Ocean was more than six hundred years ago—so far back there were no written records, nor any social memory of the disaster. Perhaps that explains why so many were caught by surprise.
But the Indian Ocean disaster was only the most vivid example of what has happened before—and what lies ahead. Chile in 1960 had a magnitude 9.5 quake in which more than 2,000 lives were lost and 3,000 people were injured. Two million were left homeless. The resulting tsunami killed another 61 people in Hawaii, 138 more in Japan, and 32 in the Philippines. Alaska in 1964 suffered a magnitude 9.2 quake, with 128 lives lost and $311 million in property damage. Mexico City in 1985 was shaken by a magnitude 8.1 temblor in which at least 9,500 were killed, more than 100,000 were made homeless, and more than $3 billion of property damage was done. What happened to Sumatra in 2004 [and to Japan in 2011] will also happen to California, Oregon, Washington, and British Columbia.
The geologic source of the looming catastrophe along North America’s west coast—like all the others—lies hidden beneath the sea, out of sight and pretty much out of mind. Scientists, civil engineers, and emergency planners know with certainty that it’s bound to happen here, but they’re having a devil of a time getting anyone to pay attention. This book, I hope, will change that.
People in the United States and Canada, if they think at all about earthquake disasters, probably conjure up the infamous San Andreas fault as the worst case. In California, waiting for “the Big One,” people wonder which city the San Andreas will wreck next—San Francisco or Los Angeles? Well, perhaps neither, because if by the Big One they mean the earthquake that will wreak havoc over the widest geographical area, that could destroy the most critical infrastructure, that could send a train of tsunamis across the Pacific causing economic mayhem that would probably last a decade or more—then the seismic demon to blame could not possibly be the San Andreas. It would have to be Cascadia’s fault.
The Cascadia Subduction Zone is a crack in the earth’s crust, roughly sixty miles (100 km) offshore and running eight hundred miles (1,300 km) from northern Vancouver Island to northern California. It has generated massive earthquakes not just once or twice, but over and over again throughout geologic time. A recently published, peer-reviewed scientific research paper documents at least forty-one Cascadia “events” in the last ten thousand years. Nineteen of those events ripped the fault from end to end, a “full margin rupture.”
As for timing, scientists used to think these mega-quakes occurred every 500 to 530 years, but the newest data show that the fault has at least four segments, the southernmost being far more active and with a greater number of slightly smaller (magnitude 8 or higher) quakes. Based on historical averages, the southern end of the fault—from Cape Mendocino, California, to Newport, Oregon—has a large earthquake every 240 years. For the northern end—from mid-Oregon to mid-Vancouver Island—the average “recurrence interval” is 480 years, according to a recent Canadian study. And while the north may have only half as many jolts, they tend to be full-size disasters in which the entire fault breaks from end to end at magnitude 9 or higher.
Given that the last big quake was more than 311 years ago, one might argue that a very bad day on the southern segment is ominously overdue. With a timeline of forty-one events an American geologist has now calculated that the California–Oregon end of Cascadia’s fault has a 37 percent chance of producing a major earthquake in the next fifty years. The odds are 10 percent that an even larger quake will strike the upper end (in a full margin rupture) in fifty years. It appears that three centuries of silence along the fault (Cascadia is classified as the quietest subduction zone in the world) has been entirely misleading. The monster is only sleeping.
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…
That’s not all. Cascadia will also slam the beaches of the west coast of North America as well as Alaska and Hawaii. A research plan prepared by NOAA—the National Oceanic and Atmospheric Administration—back in 1982 estimated that 900,000 people would be at risk from a fifty-foot (15 m) Cascadia tsunami striking the U.S. western seaboard.
But that’s just the United States. Nobody has done a projected death toll for the other Pacific Rim nations that would be affected. Researchers have, however, made a convincing case that an earthquake on Cascadia’s fault in 1700 put a series of waves thirteen to sixteen feet (4–5 m) high—imagine water more than fifteen feet above the highest tides—onto the beaches of eastern Japan, causing widespread damage, injuries, and deaths. At this point one can only imagine what the same waves would do to the seaports and villages of modern-day Japan. To this scenario add Indonesia, Hong Kong, the Philippines, New Guinea, Australia, and New Zealand—all of which would be hit by Cascadia’s waves…
Leave a Reply