The Next Big One is Coming and it will Redraw Washington’s Coastline Forever

Thousands of residents will be impacted, and hundreds of miles of coastline will be permanently underwater when the next “Big One” happens off the coast of the Pacific Northwest.

The study published by Proceedings of the National Academy of Sciences (PNAS), shows that the next large quake in the Cascadia subduction zone, in conjunction with rising sea levels, could cause the floodplain to permanently increase by 1% (as defined by FEMA) on the Washington, Oregon, and California coastlines. This would wreak havoc in towns like Ocean Shores, Westport, Long Beach, Seaside, and Astoria.

Tsunami and Subsidence: Popular Washington and Oregon Beach Towns Face Dire Quake Risk

The model in the simulation ranged from 7.7 to 9.2 in magnitude and showed the damage other historical earthquakes caused to coastal communities. For example, the Alaskan earthquake in 1964 lowered some coastal areas by over six feet (2 meters). Structures were destroyed, and residents were forced to relocate. In 2011, the Tohoku earthquake in Japan caused a 3-foot subsidence, which changed river mouths, ports, and soil stability on the coastline.

When was the last large Cascadia Subduction Zone earthquake?

The last magnitude 9.0 earthquake along the Washington, Oregon, and California coast (Cascadia Subduction Zone or CSZ) occurred in 1700.

When is the next Cascadia Earthquake expected to happen?

No one knows when the next “Big One” will occur along the Cascadia subduction zone, but according to the study from PNAS, there’s a very good chance it could occur in the next 75 years.

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The report also highlights the Cascadia Rising Scenario from 2016 and 2022, which predicts the damage and casualties that could be caused by an M9 CSZ earthquake. The landslides, tsunamis, and liquefaction from a magnitude 9.0 Cascadia Subduction Zone quake in Washington and Oregon could result in 30,000 casualties and over 170,000 destroyed structures, including schools, ports, and bridges. The economic bill would be over $81 billion.