The video below is a small-scale demonstration of something almost impossibly large: how a megathrust earthquake can suddenly turn the ocean into a weapon.
The basic mechanics are frighteningly simple. Two tectonic plates become locked while one is forced beneath the other. Stress builds for decades or centuries until the fault finally ruptures. When the seafloor abruptly jumps upward or drops, it displaces the column of seawater above it, sending tsunami waves racing outward.
Take a look at a simulation of such an event linked here and below.
One of the most dangerous places on Earth for that scenario sits just offshore of the Pacific Northwest.
The Cascadia Subduction Zone stretches roughly 600 miles from Northern California to British Columbia, where the Juan de Fuca Plate is being driven beneath North America.
A full rupture could produce an earthquake around magnitude 9. The last occurred on January 26, 1700, generating a tsunami powerful enough to cross the Pacific and strike Japan.
Scientists know Cascadia will rupture again. What they cannot do is predict when.
The latest USGS assessment estimates a 10% to 15% chance of a full-margin M9 earthquake within the next 50 years. For southern Cascadia, the probability of an M8-or-larger rupture is around 30% over the same period.
If it happens, coastal residents won’t have much time.
Oregon officials estimate shaking could last five to seven minutes, followed by a tsunami reaching parts of the coastline in only 10 to 20 minutes. DOGAMI coastal geologist Laura Gabel says knowing and practicing evacuation routes is “critical for keeping you and your loved ones safe.”
And these wouldn’t necessarily be ordinary waves.
Oregon emergency officials warn a Cascadia tsunami could reach up to 100 feet in some locations and scenarios. Modeling at Siletz Bay projects open-coast run-up around 30–35 feet in a likely scenario and 50–55 feet in a worst case.
State assessments estimate the combined earthquake and tsunami could ultimately cause more than 10,000 deaths and over $30 billion in losses in Oregon alone.
The demonstration may fit on a screen.
The real version could redraw the Pacific Northwest coastline.
Related: Catastrophic Mega-Tsunami Will Devastate West Coast, Experts Warn
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