Cascadia's Fault - Jerry Thompson [3]
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 is 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 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