Cascadia's Fault

by Jerry Thompson

  Table of Contents

  Title Page

  Dedication

  Foreword

  Introduction

  PART 1 - TREMORS AND RIPPLES

  CHAPTER 1 - Mexico City: Preview of Coming Events

  CHAPTER 2 - Lessons from the Rubble: A Front-Page Story

  CHAPTER 3 - The Alaska Megathrust: Cascadia’s Northern Cousin

  CHAPTER 4 - Against the Wind of Convention: Plafker, Benioff, and Press

  CHAPTER 5 - Cauldron and Crust: The Rehabilitation of Continental Drift

  CHAPTER 6 - Nuke on a Fault: Early Clues in Humboldt Bay

  CHAPTER 7 - Proving the Doubters Wrong: The Chile Connection

  CHAPTER 8 - Mount St. Helens: Cascadia’s Smoking Gun?

  PART 2 - SETBACKS AND BREAKTHROUGHS

  CHAPTER 9 - Mud Cores and Lasers: The Search for Evidence

  CHAPTER 10 - The Whoops Factor: Cascadia’s True Nature Revealed

  CHAPTER 11 - Quake Hunters: Finding Cascadia’s Ghost Forest

  CHAPTER 12 - Cedars, Peat, and Turbidites: A Tipping Point at Monmouth

  CHAPTER 13 - Cascadia’s Segmented Past: Apocalypse or Decades of Terror?

  CHAPTER 14 - Digital Water: Catching Waves in a Computer

  CHAPTER 15 - Defining the Zone: Hot Rocks and High Water

  CHAPTER 16 - Cracks, Missing Rings, and Native Voices: Closing In on a Killer Quake

  CHAPTER 17 - The Orphan Tsunami: Final Proof of Cascadia’s Last Rupture

  CHAPTER 18 - Episodic Tremor and Slip: Tracking Cascadia with GPS

  CHAPTER 19 - Turbidite Timeline: Cascadia’s Long and Violent History

  CHAPTER 20 - When’s This Going to Happen? The Problems with Prediction

  PART 3 - SHOCKWAVES

  CHAPTER 21 - Facing Reality: Cascadia Equals Sumatra

  CHAPTER 22 - The Next Wave: Thinking the Unthinkable

  CHAPTER 23 - Watching It Happen, Wishing It Wouldn’t

  CHAPTER 24 - Cascadia’s Fault: Day of Reckoning

  EPILOGUE

  AFTERWORD

  Acknowledgments

  SUGGESTIONS FOR FURTHER READING

  INDEX

  Copyright Page

  To Bette and Ali, the people at the heart of my universe

  CASCADIA SUBDUCTION ZONE

  TSUNAMI TRAVEL TIME

  RING OF FIRE

  COMMUNITIES WITHIN RANGE OF CASCADIA’S FAULT

  FOREWORD

  by Simon Winchester

  Of the sixteen most disastrous earthquakes to have shocked this planet since 1900, no fewer than fifteen have occurred along the shores of the Pacific Ocean, around the notorious Ring of Fire—a crucial but generally unfamiliar component of which is the subject of this book, the Cascadia Subduction Zone.

  All of the earthquakes, and all of the tsunamis that some of these quakes have spawned, have been ferociously destructive. In drawing up a league table one might reasonably have supposed the Sumatran tsunami of December 2004—caused, of course, by a huge submarine earthquake after the fracture of an offshore subduction fault system—to be history’s absolute worst; and insofar as it killed a quarter of a million people, then maybe in terms of statistical lethality it is. But what is now officially called the great Tohoku earthquake of 2011—and what spawned the grim tsunami that hit the northeastern Japanese coast on the afternoon of Friday, March 11—has implications that linger still, and that may well make this event even more deadly in the long term.

  The Japanese quake, originating as it did on the western edge of the Pacific tectonic plate, has revived interest—urgent and alarmed interest, even—in what might happen if the Cascadia fault system, which lies with ominous congruency on the plate’s eastern side, were to rupture too. Most imagine the direst of consequences—consequences that are likely to parallel with some precision just what happened in Japan. The two fault systems are very similar and are tectonically connected to each other. Both lie roughly fifty miles (80 km) offshore from their respective continents; both are subject to vast internal stresses; both, if they fracture, can cause terrible ground-shaking onshore; and both can generate immense tsunamis at sea.

  All of the broken bones that resulted in northern Japan, all of those broken lives and those broken homes and broken cities and, most sinister of all, those broken atomic reactors, swiftly prompted much of humankind to remember what in calmer times we prefer to forget: that most stern and chilling of mantras which holds, quite simply, that mankind inhabits this earth subject to geological consent—which can be withdrawn at any time.

  For thousands of people, maybe tens or even hundreds of thousands, this consent was withdrawn with shocking suddenness (all geological events are sudden, and all are unexpected, if not necessarily entirely unanticipated) at 2:46 p.m. on what was a clear, cool spring afternoon. One moment all were going about their quotidian business—in offices, on trains, in rice fields, in stores, in schools, in jails, in warehouses, in shrines—and then the ground began to shake.

  At first, the shock was merely a much stronger and rather longer version of the temblors to which most Japanese are well accustomed. There came a stunned silence, as there always does. But then, the difference: some few minutes later, a low rumble from the east, and in a horrifying replay of the Indian Ocean tragedy of just six years before, the imagery of which is still hauntingly replayed in all the world’s minds, so the coastal waters off northern Honshu vanished, sucked mysteriously out to sea.

  The rumbling continued as people began to spy a ragged white line on the horizon, and then, with unimaginable ferocity, the line became visible as a wall of waves sweeping back inshore at immense speed and at great height. Just seconds later, these Pacific Ocean waters hit the Japanese seawalls, surmounted them with careless ease, and began to claw across the land beyond in what would become a dispassionate and detached orgy of utter destruction.

  We all now know, and have for fifty years, that geography is the ultimate reason behind these disasters. Japan is at the junction of a web of tectonic plate boundaries that makes it more peculiarly vulnerable to ground-shaking episodes than almost anywhere else—and it is a measure of Japanese engineering ingenuity, social cohesion, the ready acceptance of authority, and the imposition of necessary discipline that allows so many to survive these all-too-frequent displays of tectonic power.

  But geography is not the only factor in this particular and acutely dreadful event. Topography played an especially tragic role in the story too—for it is an axiom known to all those who dwell by high-tsunami-risk coastlines that when the sea sucks back, you run—you run inland and, if at all possible, you run uphill. But in this corner of northeast Japan, with its wide plains of rice meadows and ideal factory sites and conveniently flat airport locations, there may well be a great deal of inland—but there is almost no uphill.

  Such mountains as there are sit far away, blue and distant in the west. All here is coastal plain. And so the reality is this: if a monstrous wave is chasing you inland at the speed of a jetliner, and if the flat topography all around denies you any chance of sprinting to a hilltop to escape its wrath, then you can make no mistake: the wave will catch you, it will drown you, and its forces will pulverize you out of all recognition as a thing of utter insignificance—which of course, to a tsunami, all men and women and their creations necessarily must be.

  Even more worrisome than geography and topography, though, is geological history. For this event cannot be viewed in isolation. There was a horrifically destructive Pacific earthquake in New Zealand on February 22, 2011, and an even more violent magnitude 8.8 event in Chile almost exactly a year before. All three phenomena involved more or less the same family of circum-Pacific fault lines and plate boundaries—and though there is still
no hard scientific evidence to explain why, there is little doubt now that earthquakes do tend to occur in clusters: a major event on one side of a major tectonic plate is often (not invariably, but often enough to be noticeable) followed some weeks or months later by another on the plate’s far side. It is as though the earth becomes like a great brass bell, which when struck by an enormous hammer-blow on one side, sets to vibrating and ringing all over.

  And now there have been three catastrophic events at three corners of the Pacific plate—one in the southeast, on February 27, 2010; one in the southwest, on February 22, 2011; one in the northwest, on March 11, 2011.

  That leaves just one corner unaffected—the northeast. And the fault lines in the northeast of the Pacific plate are most notoriously the San Andreas fault, underpinning the city of San Francisco; the Hayward fault, underlying the teeming and less well engineered cities of Oakland and Berkeley; and then offshore, the 800-mile-long Cascadia Subduction Zone fault. If the San Andreas or the Hayward fault were to rupture, the devastation on land could be immense; but if the Cascadia were to do likewise, the event would be global in scale, regional in destructiveness, lethal in a vast swath of countryside from Vancouver Island to the border of California. It would be a disaster of titanic proportions. It would, in a word, be epic.

  That makes the geological community very apprehensive. All know that both the San Andreas fault and Hayward fault are due to rupture any day—the former last did so in 1906, and strains have built beneath it to a barely tolerable level. But it has been fully 311 years since Cascadia fractured—and it is in my view far from wholly irresponsible (though some scientists say otherwise) to employ the word impending when describing its potential to fracture and possibly cause a terrible disaster.

  For Cascadia to rupture again, with unimaginable consequences for the millions who live in its danger zone, some triggering event has to occur. Three disasters—the Japanese tragedy of March 2011 being the most recent, New Zealand and Chile before that—have now taken place, and each of these can reasonably be regarded, perhaps, as a triggering event. There are in consequence a lot of thoughtful people in the American and Canadian west who are currently very nervous indeed—wondering, as they often must do, whether the geological consent that permits them to inhabit so pleasant a place might be about to be withdrawn, sooner than they had supposed.

  INTRODUCTION

  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 someday 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 (20 m) 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 (30 m).

  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 more than 310 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. 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.