Earthquake Prediction in Cascadia: What We Know and What We Don’t

In this episode, NPR’s Shortwave explores the Cascadia subduction zone off the Pacific Northwest, where a megathquake could reshape coastlines and cities. Scientists reconstruct past quakes using ghost forests, sand deposits, and precise historic records from Japan to show a pattern of very large earthquakes, typically magnitude 9, with irregular intervals. The show explains why precise timing is still elusive and how researchers infer what future shaking and tsunamis might look like. It also covers the emergence of earthquake early warning systems that detect tiny ground motions and can trigger life-saving actions within seconds. Finally, the discussion emphasizes practical steps for communities to prepare, from flood plans to earthquake-resistant buildings and local evacuation planning.

Overview: Cascadia and the Boundaries of Prediction

The episode centers on the Cascadia subduction zone off the Pacific Northwest, a fault line capable of producing colossal earthquakes that can trigger tsunamis. Scientists can predict the general consequences of large earthquakes—how strong shaking might be in different places and how tsunamis will behave—without predicting the exact moment they will occur. This distinction between what can be forecast and what cannot is a core theme, underscoring the value of actionable guidance even when the exact timing remains uncertain.

Evidence from the Past: Ghost Forests and Orphan Tsunamis

Researchers piece together Cascadia’s history by examining 7000 years of coastal sediments, estuaries, and marsh records. Ghost forests along the coast reveal past submersion events, and sand layers document tsunami deposits. A key line of evidence comes from Japan, where records describe an orphan tsunami on January 1700 that arrived without a preceding local earthquake. Chris Goldfinger explains that researchers used these Japanese accounts to backtrack the origin and match it to Cascadia, confirming the last great event in the Pacific Northwest occurred on that date at approximately 9 p.m. This detective work links distant records to a regional fault system and confirms the fluency of Cascadia’s megathrust history.

"The Japanese records were really accurate down to the height of the flooding and the amount of the destruction" - Chris Goldfinger, Marine Geologist and Paleoseismist

Timing, Recurrence, and the Chaos of Earthquakes

One recurring theme is that earthquake timing is not simple. Cascadia earthquakes can cluster in time, with several large events in relatively short succession followed by long quiet periods. The idea of a fixed 500-year interval is misleading; tectonic plates do not follow a predictable schedule. This variability complicates risk assessments but does not eliminate danger. Diego Melgar emphasizes the unpredictable cadence while still enabling meaningful planning and mitigation strategies.

"Earthquakes are like chaotic turkeys" - Chris Goldfinger, Marine Geologist and Paleoseismist

From Records to Readiness: What We Can Predict and Prepare For

Beyond timing, scientists have strong expectations about the physical impact of a Cascadia quake and the accompanying tsunami. Sediment cores show that land can suddenly drop and sea levels can rise dramatically, inundating flat coastal areas and critical infrastructure. Tina Dura notes that coastal land is rising slowly between earthquakes, roughly 1 millimeter per year, but the next event will reverse that trend with a rapid land subsidence and up to two meters of sudden sea-level rise, intensifying flood risks. The episode also connects Cascadia to seismically linked faults like California’s San Andreas, suggesting a broader West Coast domino effect in the event of a major quake.

"the land is rising at about 1 millimeter a year" - Tina Dura, Coastal Geologist and Paleoseismologist

Early Warning and Preparedness: Turning Knowledge into Action

Despite timing uncertainties, scientists have advanced early warning technology. An early warning system uses thousands of seismometers to detect initial, tiny ground motions that precede larger earthquakes. If these patterns indicate a growing magnitude, automated systems can trigger alerts within seconds to drop, cover, and hold on. The goal is not perfect prediction but rapid warning that saves lives and enables protective actions before the strongest shaking reaches communities. The discussion also highlights practical steps for coastal towns, such as flood planning, community drills, and advocating for earthquake-resistant buildings and evacuation centers. The overarching message is clear: knowledge about potential impacts empowers communities to build resilience and reduce harm.

"This entire early warning system can be activated in 15 to 20 seconds, totally automated without any human action" - NPR narration/participants

actionable Takeaways: Community and Policy Implications

The episode closes with calls to action for individuals and local governments: learn your local earthquake plan, ensure evacuation routes and centers exist, and work toward resilient infrastructure. Although scientists cannot precisely forecast the moment of the next Cascadia quake, the combination of paleoseismology, modern modeling, and automated warning systems provides a robust framework for reducing risk. The episode emphasizes collaboration between scientists, policymakers, and communities to translate scientific knowledge into practical, life-saving preparedness.