Two separate, peer-reviewed studies published in 2026 don't replace the famous faults. They complicate them.
For decades, American earthquake preparedness has had two headline names: Cascadia, the offshore subduction zone that could one day produce a magnitude 9 event across the Pacific Northwest, and the San Andreas, the fault most people picture when they hear “the Big One.”
One found that the ground directly beneath Seattle may pose a more immediate threat to the city than the famous offshore fault everyone plans around. The other found that the San Andreas — and a neighboring fault most people have never heard of — are under more stress right now than at any point in the last thousand years, with a newly identified mechanism that could make a future rupture bigger than previously modeled.
Neither study is a prediction. Both come with real, stated uncertainty from the scientists who did the work. But both are worth understanding, because they change what “knowing your risk” actually means if you live in either region.
The fault under Seattle, not offshore
When people in the Pacific Northwest think about earthquake risk, they think about Cascadia — the massive subduction zone sitting off the coast, capable of a full-margin rupture that USGS estimates carries roughly a 10–15% chance in the next 50 years.
A new study led by Dr. Stephen Angster, a research geologist with the USGS Earthquake Science Center, looked somewhere else: the network of smaller “secondary” faults running directly beneath Seattle itself, as part of the broader Seattle Fault Zone.
What his team found, published in the Geological Society of America Bulletin in January 2026, is that these secondary faults rupture roughly every 350 years — far more often than the zone's main fault, which operates on a 5,000-plus-year cycle. Using trench excavation, radiocarbon dating, and tree-ring analysis on Bainbridge Island and near Bellevue, the team traced surface-rupturing earthquakes back more than 10,000 years, and found that over the last 2,500 years, these smaller faults — not the main one — have produced most of the zone's surface ruptures. The most recent rupture dates to roughly the early 19th century.
Here's the detail that matters most: these secondary faults are currently excluded from the National Seismic Hazard Model, the federal framework that shapes building codes and emergency planning nationwide, because they don't meet the minimum length requirement for inclusion. In other words, official hazard models may be underweighting a risk that sits closer to home, for the roughly 4 million people who live in the Seattle metro area, than the fault most of them have been told to worry about.
That's not a claim that Cascadia doesn't matter — it's a reminder that “the big, famous threat” and “the most dangerous threat to you specifically” aren't always the same fault.
The “earthquake gate” under Southern California
The second study looks at ground that's been studied for decades — the southern San Andreas Fault — and finds something new hiding in the data.
A team led by Dr. Liliane Burkhard, a geophysicist affiliated with the University of Bern and the University of Hawai‘i, built a physics-based model of 1,000 years of stress accumulation along the southern San Andreas and the neighboring San Jacinto Fault. Their finding: stress on these fault systems is now at its highest point in that entire thousand-year record.
That alone isn't new — scientists have known the San Andreas has been building tension since its last major rupture, the 1857 Fort Tejon earthquake. What's new is that the San Jacinto Fault, which runs alongside it and carries some of the fastest tectonic motion in the state, is elevated at the same time. And where the two faults meet — a mountain corridor called Cajon Pass, about 63 miles northeast of downtown Los Angeles — Burkhard's team found something they're calling an “earthquake gate”.
The gate doesn't always work the same way. In 1857, the Fort Tejon rupture hit Cajon Pass and stopped, staying contained to the San Andreas. In 1812, the Wrightwood earthquake crossed the same junction and ruptured both fault systems as a single event. Burkhard's modeling suggests current stress conditions make that second outcome — a joint rupture — more plausible than it's been in centuries.
If that happened today, the study estimates a magnitude in the 7.4–7.8 range, with damage spreading across a wider area than a single-fault event: highways, rail lines, and energy infrastructure serving San Bernardino, Riverside, and the Coachella Valley simultaneously, rather than one city absorbing the brunt alone.
Caltech seismologist Dr. Lucy Jones, one of the most established voices in California earthquake science, pointed to a real-world example of exactly this kind of cascading rupture: the earthquake that struck Venezuela in June 2026, which began west of Caracas and propagated toward the city along a similar transform-fault mechanism, concentrating damage in a populated area (CNN).
Should you actually worry?
Neither study is telling you an earthquake is coming next week, next year, or on any particular timeline. Both lead researchers say so explicitly, and that distinction matters more than the headline.
What both studies are saying is narrower and, in a way, more useful: the hazard maps most emergency planning is built on may not fully capture the risk that actually exists on the ground. In Seattle, that means a fault system with a shorter rupture cycle than official models currently weigh. In Southern California, it means a well-known fault paired with a less-discussed neighbor, at a moment when both happen to be under record stress.
If you live in the Puget Sound region, your closest serious threat may not be the offshore fault you've heard about — it may be the ground under the city itself. If you live along the I-15 corridor between Los Angeles and the Inland Empire, the scenario worth understanding isn't just “San Andreas ruptures,” it's “San Andreas and San Jacinto rupture together.”
Neither of those is a reason to panic. They're a reason to check whether your own plan — where you'd go, how you'd communicate, what you'd need for the first 72 hours — actually accounts for the fault that's closest to you, not just the one with the most name recognition.
If you haven't run through that yet, our Preparedness Assessment and Bug Out Bag Builder are built for exactly this: not to tell you a disaster is coming, but to make sure you're not caught explaining, after the fact, that you knew the odds and never checked your own plan against them.