Current Events: Cascadia Earthquake - Civics Learning Project

Oregon students drill for it. Oregon universities study it. Oregon governments prepare for it. But what is the Cascadia Earthquake?

The Pacific Northwest is part of the Ring of Fire, a volcanic circle around the Pacific Ocean that produces 90% of the world’s earthquakes. Oregon contains part of the 620 mile-long fault line known as the Cascadia Subduction Zone (CSZ). This ‘megathrust’ fault is the meeting of the Juan de Fuca plate and the North American plate. As the Juan de Fuca plate moves below the North American plate, part of the ‘subduction’ is stuck, building energy that will release as an earthquake.The width of this locked region and length of the fault zone produces very large quakes. Scientists don’t know exactly when, but estimate a 37% chance of a megathrust earthquake of 7.1+ magnitude within the next 50 years, somewhere along that zone from Cape Mendocino, California, to Vancouver Island, Canada. Emergency response managers and seismic experts agree, this is not a case of “if” the next great earthquake will occur, but “when.”

Historical evidence including tree rings, soil samples, carbon dating, tsunami modeling, Native American oral tradition, and Japanese records pinpoint January 26th, 1700, at 9 pm as the last major quake in the CSZ. It was likely in the magnitude of 9 and produced a tsunami that inundated the Oregon coast.

When the next Cascadia earthquake occurs, scientists expect the first and biggest wave to reach the beach 10 – 20 minutes after the mainshock. The shaking will warn folks to move immediately to higher ground following predetermined evacuation routes. Smaller tsunamis will continue to hit and flood the coast for another 12 hours. The pressure release and subduction models for the next quake show the Oregon coastline lowering at least 3 – 6 ft in a process known as subsidence. This would lead to significant coastal erosion for beaches, dunes and bluffs for years, changing ecosystems and communities in our state.

Natural disasters may not be stopped, but preparation can reduce impact and save lives and some of the built environment. Teams of scientists, engineers, and public officials are helping coastal communities to prepare for seismic events. Agencies are identifying tsunami inundation areas, preparing warming systems, mapping and providing signage of evacuation zones, routes, and assembly areas, and educating the public. Central Oregon is building an emergency management center in expectation of being the state’s hub for responding to the Cascadia quake.

Oregon also began updating construction standards for earthquakes in the 1990s. Building response factors include the age of the building, material (wood is less brittle than brick or concrete), underlying geology and location. Governor Tina Kotek issued Executive Order NO. 25-22 on September 8, 2025 directing all new state-owned buildings to be built to be earthquake-proof, and replacement or upgrade for earthquake-safety of all buildings owned or leased by the state for executive branch agencies by 2060. Oregon’s aging infrastructure like roadways, bridges, rail, air, ports, and pipelines were not designed to withstand large earthquakes and could fail. Transportation infrastructure upgrades are tied to one of the most contentious debates in the state at present – how to pay for it.

This week’s current event explores the Cascadia Earthquake, past and future, and how Oregon is preparing for the coming natural hazard.

Essential Questions:

Essential Question #1 – How do states prepare for natural disasters?

Essential Question #2 – What do we know about the Cascadia Subduction Zone?

Essential Question #3 – What don’t we know about the Cascadia Subduction Zone?

Essential Question #4 – How can Oregon best prepare for emergency response?

Vocabulary:

Cascadia Subduction Zone: A 620 mile- long fault zone in which the Juan de Fuca plate is being subducted beneath the North American Plate.

aftershocks: smaller earthquakes that follow the largest shock of an earthquake sequence, and can continue over a period of weeks, months, or years.

subsidence: the lowering of the ground surface due to an earthquake

Ring of Fire: the zone of earthquakes surrounding the Pacific Ocean- about 90% of the world’s earthquakes occur there.

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