What’s a Subduction Zone? Everyone in the Pacific NW Should Know

The Pacific Ocean is home to the majority of the world’s earthquake and volcanic activity, thanks to its extensive subduction zones. The Ring of Fire, a nearly continuous belt of subduction zones encircling the Pacific, is responsible for about 90 percent of the world’s earthquakes and 75 percent of its active volcanoes.

Dramatic Activity at the Cascadia Subduction Zone

The Cascadia subduction zone is a massive fault running about 700 miles (1,126.5 kilometers) from northern California to British Columbia.

In the year 1700, this fault ruptured in a megathrust earthquake. Scientists know this from both geological evidence and historical records in Japan — where a massive tsunami hit without warning — and oral histories from Native Americans.

The earthquake was a massive seismic event that shook the Cascadia region of North America, affecting what is now Vancouver Island, British Columbia, Washington, Oregon and Northern California.

Accounts of the 1700 Megathrust Earthquake

The Huu-ay-aht First Nation recounts that the earthquake struck at night, causing longhouses in Anacla, Pachena Bay, to sink into the sand. Similarly, the Cowichan Tribes First Nation described massive landslides and unrelenting tremors that flattened entire villages.

On the Olympic Peninsula and southern Oregon, Indigenous oral traditions recall a huge tidal wave that uprooted trees, destroyed settlements and altered river courses. In Japan, historical records detail destructive waves striking coastal towns on Jan. 27 to 28, without a preceding earthquake, confirming that a Cascadia tsunami had traveled across the Pacific.

Looking Ahead

Because the oceanic lithosphere of the Juan de Fuca Plate is being pushed down into the mantle, tremendous amounts of energy build up over centuries. When this energy is released, earthquakes occur with enough force to shake entire cities, displace land, and generate tsunamis.

The problem? Signs point to another big one on the way.