Scientists have long warned of the dangers lurking beneath the West Coast of North America, but a pair of new studies has brought chilling clarity to just how interconnected—and potentially devastating—those dangers may be. On October 10, 2025, researchers published a landmark paper in Geosphere titled “Unravelling the dance of earthquakes: Evidence of partial synchronization of the northern San Andreas fault and Cascadia megathrust.” The findings, described by Oregon State University’s Chris Goldfinger as a “smoking gun,” suggest that an earthquake in the Cascadia subduction zone could trigger a near-simultaneous rupture along California’s notorious San Andreas fault. If that sounds like a nightmare scenario, that’s because it is.
“It would be a very bad day on the West Coast of the US, that’s for sure,” Goldfinger told RV Times. The research, which Goldfinger and his colleagues have been developing for decades, points to a direct geological link between two of the continent’s most dangerous fault systems. The implications are enormous, not just for scientists and emergency planners, but for the millions who live in the shadow of these faults—from Vancouver, Seattle, and Portland down to San Francisco and Los Angeles.
For years, geologists suspected that the Cascadia and San Andreas faults might be connected in some way, but proving it was another matter. In 2008, Goldfinger’s team first published a hypothesis that a major quake on Cascadia could set off the San Andreas. Back then, their primary tool was radiocarbon dating, which, while powerful, couldn’t pinpoint exactly how close in time these ancient earthquakes occurred. So, they turned to relative dating—analyzing the layers of sediment and geological deposits left behind by past quakes.
“When a fault ruptures, it’s relieving stress locally, but it’s transferring stress to areas nearby,” Goldfinger explained to RV Times. “So when Cascadia ruptures, it transfers stress to Northern California.” By studying the geologic record, his team found that San Andreas earthquakes often followed closely on the heels of Cascadia events—sometimes almost instantly. The best example? The year 1700.
That year, the Cascadia subduction zone unleashed a massive magnitude 9.0 earthquake, sending 30-foot-high waves across the Pacific to crash into the coast of Japan. The event is meticulously documented in both the geological record and in the oral histories of Indigenous peoples along the Pacific Northwest. But, as Goldfinger noted, “It turns out there was also a 1700 San Andreas earthquake.” While there’s no colonial-era written record from California—Spanish settlements wouldn’t appear in the region for another 70 years—the sediment evidence is hard to ignore. The San Andreas quake struck before the sediment from the Cascadia quake had even settled, suggesting a gap of only minutes to hours between the two disasters.
According to Express, researchers now warn that a similar tandem event could spell disaster for the West Coast, stretching emergency response services to the breaking point. “We could expect that an earthquake on one of the faults alone would draw down the resources of the whole country to respond to it,” Goldfinger told Express. “And if they both went off together, then you’ve got potentially San Francisco, Portland, Seattle, and Vancouver all in an emergency situation in a compressed timeframe.”
The consequences would be catastrophic. Seismologists predict the collapse of high-rises and other structures, enormous fires capable of incinerating hundreds of homes, buckling of Los Angeles highways, and even the possibility of a tsunami. The 1700 event sent waves across the ocean; a repeat could do the same, threatening communities far beyond the initial quake zone.
Just how likely is this double-whammy scenario? According to the Penn State College of Earth and Mineral Sciences, the odds of a major Cascadia quake occurring in the coming decades are about one in eight. That’s not a certainty, but it’s hardly reassuring. And while the exact timing between a Cascadia rupture and a San Andreas quake remains uncertain—it could be minutes, weeks, or even decades apart—the geological record shows that back-to-back disasters are entirely possible.
Goldfinger’s team, in their September publication, emphasized that while the 1700 quakes occurred within minutes to hours of each other, “the probability of that version happening again could range from minutes to decades or even 50 years.” In other words, there’s still much scientists don’t know about how these faults interact. But the evidence for a connection is now too strong to ignore.
For emergency managers and government officials, the message is clear: prepare for the worst. “Regionally, having two disasters in close timing proximity would be a huge thing for the country to try to respond to,” Goldfinger told RV Times. The challenge isn’t just the scale of destruction, but the sheer logistical nightmare of coordinating relief efforts across multiple major cities simultaneously. “Our preparedness level is poor,” Goldfinger admitted to The Guardian. “We have a long way to go, and all these areas were built on top of ticking time bombs.”
That warning couldn’t be more timely. The West Coast’s population has boomed since the last major quakes, and much of the infrastructure—from bridges and highways to schools and hospitals—wasn’t designed with a double-fault event in mind. The memory of past disasters lingers: the 1906 San Francisco earthquake, the 1989 Loma Prieta quake, and the 1994 Northridge earthquake all caused widespread havoc. But none of those events involved both the Cascadia and San Andreas faults rupturing in quick succession.
Some hope that a Cascadia quake could act as an early warning for a San Andreas event, giving emergency responders a precious head start. But as Goldfinger cautions, there are still many variables and unknowns. The geological evidence suggests that while the two faults can rupture in tandem, the interval between them could vary wildly. “It could be weeks. It could be a couple of decades. It could be 50 years even,” he said. That uncertainty makes planning all the more complicated.
Still, the findings have galvanized calls for greater investment in seismic preparedness. Retrofitting critical infrastructure, updating building codes, and improving public awareness are all steps experts say are urgently needed. The science may not be able to predict the exact day or hour of the next great quake, but it’s painting a clearer picture of what’s at stake—and what’s possible if the warnings go unheeded.
As scientists continue to unravel the complex dance of tectonic forces beneath the West Coast, one thing is certain: the region’s future depends not just on the whims of nature, but on the choices made today to prepare for what could be the most challenging natural disaster in American history.
