California at risk? The “Really Big One” could strike and cause massive damage, scientists warn

Scientists have found that a massive earthquake in the Pacific Northwest could trigger a second catastrophic quake along California’s San Andreas Fault . A study published in SciTechDaily reveals that seismic stress from one fault system can transfer to another, creating a dangerous domino effect across the region. This challenges the long-held belief that these major faults operate independently. Such interconnected fault activity could dramatically increase the scale of destruction, posing serious risks to millions living along the US West Coast. Experts emphasise the urgent need for improved earthquake preparedness , stronger infrastructure, and advanced early warning systems to reduce potential devastation if both fault lines were to rupture in quick succession.


Northwest earthquake may trigger the San Andreas Fault

Beneath the Pacific Northwest lies a powerful subduction zone. When it shifts, it can do so violently. A magnitude 9 or larger earthquake in this area would produce intense ground shaking, destructive tsunamis, and landslides that could devastate communities across the region. Recent research published indicates that the effects of such an earthquake might not be limited to the Pacific Northwest. The study warns that it could also trigger significant activity along California’s San Andreas Fault, creating the possibility of two major earthquakes occurring in close succession.

Dr Chris Goldfinger, a paleoseismologist at Oregon State University and lead author of the study, explains that a simultaneous event is highly unusual. He says, "It is hard to exaggerate what a magnitude nine earthquake would mean for the Pacific Northwest. The chance that the San Andreas Fault would follow is extraordinary."


Two major faults could shake the Pacific Coast at the same time

The US Pacific coast sits atop a complex network of tectonic boundaries. North of Cape Mendocino, the Juan de Fuca plate slides beneath the North American plate, forming the Cascadia megathrust. This zone is capable of releasing enormous amounts of energy during a major quake.

Further south, the Pacific and North American plates slide past each other along the San Andreas Fault, which has produced devastating earthquakes, including the famous 1906 San Francisco quake. The possibility that both fault systems could rupture around the same time represents a much higher seismic risk for western US communities than previously realised.


Sediment cores near San Andreas Fault reveal 3,000 years of history

The findings of the study arose unexpectedly during a 1999 research expedition. The original mission was to examine sediment cores and seismic records off the Pacific Northwest to study Cascadia earthquakes. However, a navigational mistake took the research vessel 90 kilometres south, placing it above the San Andreas Fault near Cape Mendocino.

Instead of abandoning the mission, Dr Goldfinger and his team decided to take a core sample from the submarine Noyo Canyon near Fort Bragg, California. The results were surprising. The sediment, spanning roughly 3,000 years, contained multiple turbidites. These layers form from underwater landslides called turbidity currents.


Researchers find a connection between Cascadia and San Andreas Fault

The team noticed an unusual pattern: doublet turbidites, which are pairs of sediment layers deposited at the same time, appeared in both the Noyo Canyon and Cascadia cores. Radiocarbon dating confirmed that over half of these layers were deposited simultaneously along the coast, suggesting a linked origin.

Dr Goldfinger explains, "The Noyo channel was likely recording Cascadia earthquakes, and at similar distances, Cascadia sites were recording San Andreas earthquakes. It seems possible that a large quake in Cascadia could trigger a smaller event near the San Andreas Fault, which could then lead to a larger deposit from a subsequent quake."

This accidental discovery points to a connection between the Cascadia megathrust and the San Andreas Fault that had not been fully understood before.


The “Big One” might hit in a series along the West Coast

The timing between these linked earthquakes remains uncertain. Some turbidite evidence suggests that the second quake occurred within minutes or hours of the first. This raises the alarming possibility that much of the US Pacific coast could experience major earthquakes nearly simultaneously.

The implications for life and infrastructure are serious. Dr Goldfinger, originally from the Bay Area, notes, "If I were in my hometown of Palo Alto, and Cascadia went off, I would head east. The risk that the San Andreas could follow seems very high." While scientists continue to study the mechanisms connecting these two fault systems, the findings highlight the urgent need for enhanced earthquake preparedness along the West Coast. Awareness of potential cascading hazards is critical for communities, emergency services, and policymakers.




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