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Cascadia Subduction Zone Earthquake Study Is Bad News For Portland

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Cascadia Subduction Zone Earthquake Study Is Bad News For Portland

A 700-mile long fault line called the Cascadia subduction zone is giving residents off the coast of California, Washington, and Oregon, new reasons to worry. A new study by the University of Oregon has concluded that enormous stress is building up, which could be an indication of a large-scale earthquake event just off the coast.

While much of the focus on the west coast aims at the San Andreas fault, the real beast may be the enormous potential that the Cascadia Subduction Zone offers the region. Hence, why the new University of Oregon has many people in the area rattled.

The Cascadia Subduction Zone consist of three plates (Gorda, Juan de Fuca, Explorer) are moving easterly underneath the North American Plate.

Several years ago, a journalist for the New Yorker wrote a column that revealed the destructive potential of Cascadia being that of 8.7 to 9.2 in magnitude.

For perspective, the 1994 Northridge earthquake, which hit the Los Angeles San Fernando Valley early on the morning of January 17th, was a 6.7 magnitude. It only lasted up to 20 seconds for the worst affected areas. The blind-thrust earthquake left over 8,000 injured, 57 dead, and billions in property damage.

The short duration of the quake and the fact that it was sub-7.0 illustrates some concept of what dire consequences could be experienced by a magnitude 9.0.

It’s as unimaginable as it is terrifying.

So what’s happening with Cascadia and why are geologists so concerned?

The geologists in the study are concerned over what they are terming, “anomalies” found using four years of data from 268 seismometers. Some of the seismometers are located on the land, others at the bottom of the ocean. The anomalies exist in the Cascadia Subduction Zone’s upper mantle.

Geologists believe that data taken from such anomalies can help predict where an earthquake can happen, how powerful it might be, and the frequency at which earthquakes along the fault may occur.

What’s so terrible about Cascadia Subduction Zone’s state of affairs?

Geologists have discovered that higher temperatures and rising molten rock are adding unhealthy stress to a part of Cascadia Subduction Zone’s northern region, which is just off the San Andreas fault line.


“What we see are these two anomalies that are beneath the subducting slab in the northern and southern parts of the subduction zone,” Miles Bodmer said. Bodmer is a University of Oregon doctoral student who was in charge of the study. “These regions don’t have the same behavior as the entire fault. Three segments have distinct geological characteristics. The north and south segments have increased locking and increased tremor densities.”

The dire prediction all comes down to how the state of stress on the fault line.

“If they are stuck together tightly, as is the case here, they are building up stress, and you have the potential for the release of that stress, or energy, in large earthquake events,” Bodmer said.

Bodmer says that deep tremors are taking more time to release energy than normal quakes.

The study reveals an even more threatening outlook for Portland. Geologists believe that increased activity in the Puget Sound area isn’t a good sign.

“We’re looking at structures deep within the Earth and finding evidence suggesting that they are influencing the megathrust faults and controlling where we see increases in locking and segmentation,” Bodmer said. “Knowing the timing and path of the seismic signals, we can look at velocity variation and equate that to the structures. With large offshore data sources, we might be able to better understand how a large rupture in the south might extend into central Oregon.”

Forecasts for Cascadia’s wrath are even worse when we consider the likelihood of a Tsunami. Tsunamis happen when a subduction zone fault line displays massive amounts of ocean water, resulting in the push of a gigantic tidal effect, or wave. A tsunami released from a potent Cascadia subduction zone would inundate numerous west coast regions with water in less than 20 minutes, offering up little time to escape. The damage left behind would be unfathomable.

Residents in the region are no strangers to the ground trembling below them; it is a part of life in this part of the country where fault lines a frequently active.

The last notable earthquake in Oregon occurred on February 28, 2001. Named the “Nisqually earthquake,” the 6.8 magnitude earthquake lasted for roughly 30 seconds and caused large buildings to sway. While buildings reported cracks, no loss of life occurred.

Author: Jim Satney

PrepForThat’s Editor and lead writer for political, survival, and weather categories.


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