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Underestimated Earthquake Threat to North America

The enormous fault off the coast of the Pacific Northwest has been silent for three centuries. But after years of detective work, geologists have discovered that it can unleash mayhem on an epic scale.

A magnitude-9 earthquake hit the Tohoku region of northeastern Japan back in 2011, triggering one of the most destructive tsunamis in a thousand years. The Japanesethe most earthquake-prepared, seismically savvy people on the planetwere caught off-guard by the Tohoku quakes savage power.


Japans devastating Tohoku earthquake and tsunami, scientists are still trying to figure out how the worlds most organized and earthquake-ready nation could have been taken so much by surprise. They were hit by an earthquake roughly 25 times more powerful than experts thought possible in that part of the country. How could the forecast have been so wrong? The short answer is they didnt look far enough back in geologic time to see that quakes and tsunamis just this big had indeed occurred there before. If they had prepared themselves for a much larger quake and wave, the outcome might have been entirely different.

People in the United States and Canada, if they think at all about earthquake disasters, probably conjure up the San Andreas fault in the worst-case scenario. In California, as they wait for the Big One, people wonder which city the San Andreas will wreck nextSan Francisco or Los Angeles? But if by the Big One they mean the earthquake that will wreak havoc over the widest geographic 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 morethen the seismic demon to blame could not possibly be the San Andreas. It would have to be Cascadias fault.

The Cascadia subduction zonean almost identical geologic threat off the west coast of North America as earthquake hit the Tohoku region of northeastern Japan

The Cascadia subduction zone is a crack in the Earths crust, roughly 60 miles offshore and running 800 miles from northern Vancouver Island to Northern California. This fault is part of the infamous Pacific Ring of Fire, the impact zone where several massive tectonic plates collide. Here, a slab of the Pacific Ocean floor called the Juan de Fuca plate slides eastward and downward, subducting underneath the continental plate of North America.

The U.S has had its fair share of natural disasters over the years. Yellowstone National Park is a national park located primarily in the U.S. state of Wyoming, extending into Montana and Idaho.
Sean Lennox of writes that the supervolcano beneath the surface of Yellowstone National Park is 2.5 times larger than previously believed according to a study from the University of Utah.

In 1980, Mount St. Helens volcano erupted, releasing an 80,000 ft. plume of volcanic ash sufficient to pass through the troposphere and well into the stratosphere. The Yellowstone supervolcano is estimated to be an astonishing 2,000 times worse the impact of St. Helens volcano, and would wrap ash around the planet and be a global event.


Cascadia Subduction Zone, tectonic time bomb is alarmingly similar to Tohoku, capable of generating a megathrust earthquake at or above magnitude 9, and about as close to Portland, Seattle, and Vancouver as the Tohoku fault is to Japans coast. Decades of geological sleuthing recently established that although it appears quiet, this fault has ripped open again and again, sending vast earthquakes throughout the Pacific Northwest and tsunamis that reach across the Pacific.

A hypothetical scenerio of devastation is described by Jerry Thompson

At the U.S. Geological Survey (USGS) lab in Menlo Park, seismometers peg the quake at magnitude 8.1, and the tsunami detection centers in Alaska and Hawaii begin waking up the alarm system with standby alerts all around the Pacific Rim. Early morning commuters emerging from a BART station in San Francisco feel the ground sway beneath their feet and immediately hit the sidewalk in a variety of awkward crouches, a familiar fear chilling their guts.

Another potential time-bomb waiting to happen is in Californias North Coast. A recent article in the Los Angeles Times reports a potent threat of major earthquake off Californias northern coast. This threat has been known for quite a long time, however just like in the Yellowstone supervolcano case, the potential impact has long been underestimated. The LA Times reports: Risk of a monster quake and tsunami off Californias North Coast is greater than researchers once thought.

The report states that if a 9.0 earthquake were to strike along Californias sparsely populated North Coast the catastrophic ripple effect would result in the following disasters:

A giant tsunami created by the quake washing away coastal towns, destroy U.S. 101 and cause $70 billion in damage over a large swath of the Pacific coast.

More than 100 bridges would be lost, power lines toppled and coastal towns isolated.

Residents would have as few as 15 minutes notice to flee to higher ground, and as many as 10,000 would perish.


Los Angeles Times