New Oregon Quake Is a Warning: Cascadia’s ‘Great Quake’ Could Redraw the Coastline Overnight

New Oregon Quake Is a Warning: Cascadia’s ‘Great Quake’ Could Redraw the Coastline Overnight

The Pacific Northwest was reminded of its seismic vulnerability after a magnitude 4.2 earthquake struck roughly 200 miles offshore from Barview, Oregon. That tremor was the third in a two-week swarm that researchers say may be linked to Axial Seamount, an underwater volcano that last erupted in 2015.

“There’s still a chance it could erupt by the end of the year. We don’t really know exactly when it will happen, but nothing seems imminent since the number of earthquakes per day is relatively low,” said Bill Chadwick, a researcher at Oregon State University.

The larger hazard: Cascadia

While small offshore quakes draw attention, the far greater long-term risk is the Cascadia Subduction Zone, a roughly 700-mile fault that stretches from northern California to British Columbia. There, the Juan de Fuca plate is slowly being forced beneath the North American plate, storing strain over centuries until it is suddenly released.

When that release occurs, scientists warn it could create a megathrust earthquake — commonly called the “great quake” — likely in the magnitude 8–9 range. Such an event could shake the region for minutes and trigger a large tsunami.

Subsidence: a rapid, lasting threat

Beyond shaking and tsunami waves, a less obvious but profoundly consequential risk is subsidence: the sudden sinking of land. New research led by coastal geologist Tina Dura and published in Proceedings of the National Academy of Sciences shows that coastal areas could drop by as much as 6 feet (about 2 meters) within minutes during a megathrust event.

“During one of these over magnitude 8, probably up to magnitude 9 earthquakes, the land actually deforms and drops down up to 6 feet or 2 meters. Basically causing sea level rise of 6 feet within minutes,” Dura said.

That abrupt drop resets the ground-level baseline: places that were once above high tide could become permanently flood-prone or even submerged, altering shorelines and dramatically increasing exposure to coastal flooding.

What the new research found

Dura’s analysis accounts for both instant subsidence and future sea-level rise. Key findings include:

• If a megathrust earthquake occurred today, the 100-year floodplain would expand by about 115 square miles, roughly doubling the number of residential structures and roads exposed to severe flooding.
• By 2100, when projected sea-level rise is included, the floodplain could expand an additional ~145 square miles, tripling exposure compared with current maps.

Most current flood maps and insurance models do not fully incorporate long-term subsidence from a Cascadia event, producing a blind spot in risk assessment and homeowner awareness.

Practical risks and recommendations

Subsidence and increased coastal flooding threaten more than basements. Wastewater treatment plants, electrical substations, roadways, and other critical systems sited at low elevations could be compromised, disrupting public safety and daily life.

One inch of floodwater can cause up to $25,000 in damage, according to FEMA, and most standard homeowners’, renters’, and business insurance policies do not cover flood or tsunami damage. Janet Ruiz of the Insurance Information Institute warns that flood and tsunami losses typically require separate coverage.

Homeowners should take practical steps now:

• Check Dura’s projected post-earthquake floodplain maps (PDFs or interactive maps, when available) to see if your property could be newly at risk.
• Compare the National Flood Insurance Program (NFIP) with private flood-policy options; NFIP limits (typically $250,000 structure / $100,000 contents) may be insufficient for high-value homes.
• Reassess property risk using elevation, proximity to water, and likely long-term sea-level change.
• Plan for nuisance flooding, increased king tides, and erosion that may occur even before a major quake.

How soon could it happen?

Geologic records indicate Cascadia megathrust earthquakes occur roughly every 250 to 800 years. “We’re over 300 years out from the last earthquake,” Dura notes, placing the region within the geologic window of possibility. While timing is uncertain, the potential impacts are clear: sudden subsidence plus rising seas would transform flood risk almost overnight.

Preparing now — updating maps, reassessing insurance, and protecting critical infrastructure — can reduce harm and financial loss when the next great quake arrives.