The catastrophic San Andreas earthquake could be caused by the Cascadia subduction zone

For generations, scientists have believed that the West Coast's two big earthquake drivers — the Cascadia Subduction Zone and the San Andreas Fault — operate on separate geological stages. One dive, one glide, and both have enormous destructive potential.

But new research by marine geologist Chris Goldfinger at Oregon State University shakes that assumption. His team's study suggests that these two giants may sometimes move in rhythm, with their earthquakes occurring close to each other in time — sometimes within years, or even hours.

This surprising association suggests that the “big movie” may not always be a single work. In rare cases, Cascadia and northern San Andreas populations may act as dance partners, their seismic steps linked across a turbulent boundary off northern California called the Mendocino Triple Junction.

Reading earthquakes in ocean mud

To uncover this story, Goldfinger's group turned to one of Earth's most meticulous archives: the seafloor. When major offshore earthquakes strike, they trigger vast underwater landslides, sending plumes of mud and sand hurtling through deep ocean canyons. These flows settle into layers known as turbidites, each a time-stamped page in the planet's earthquake diary.

Chris Goldfinger, a marine geologist at Oregon State University, has sediment samples. (Credit: Oregon State University)

The team analyzed 137 sediment cores collected along the two rift systems, including samples from Noyo Channel, Trinidad Canyon, and South Cascadia. With more than 14,000 km of shallow seismic reflection data, radiocarbon dating of microscopic shells, and high-resolution CT scans, they reconstructed nearly 10,000 years of seismic history.

Goldfinger and his colleagues compared the thickness, volume and layering of these deposits. They even used traces of “carbon bomb” – isotopes left over from nuclear testing in the mid-20th century – to determine modern stratigraphy with extraordinary accuracy.

A pattern that crosses fault lines

What emerged was an extraordinary pattern: Over the past 3,100 years, many of the major earthquake strata in southern Cascadia matched in time with those in the northern San Andreas. Of the 18 Cascadia and 19 San Andreas events identified, 10 appear to have occurred nearly simultaneously, with their ages differing by only a few decades — within the margin of uncertainty.

Eight of these identical pairs showed a particularly striking feature: two closely overlapping layers, one smooth and one rough. The team called these “binaries.” They believe the soft layer represents the Cascadia earthquake, which was followed shortly after by the San Andreas rupture that deposited coarse sediments on top. These double layers are thickest near the Mendocino Triple Junction, and thin out north and south from that point—a geographic signature that supports the idea of ​​stress transfer from one fault to the next.

Sediment cores. (Credit: Oregon State University)

When one error leads to another error

The concept of one earthquake triggering another is not new. Scientists know that large earthquakes can redistribute tectonic stress and bring nearby faults closer to failure. But proving such a connection between two massive, long-period systems has been elusive.

Goldfinger's team argues that large Cascadia earthquakes may slightly increase pressure along the northern San Andreas, while major San Andreas ruptures could in turn send pressure waves back to the southern edge of Cascadia. Over thousands of years, this push and pull may have caused a few coupled events, the geological equivalent of a domino effect between two of the strongest fault zones on Earth.

“Geologists have long suspected that faults could coincide, but we have only seen one clear example before — in Sumatra, in 2004 and 2005,” Goldfinger explained. “Now we have strong evidence that this happened here as well.”

Shaded perspective view of the southern Cascadia subduction zone, the Mendocino trijunction, and the northeast-trending northern California margin. (Credit: Goldfinger, et al.)

From coincidence to discovery

This revelation has its roots in an accident. During a 1999 research expedition, Goldfinger's team accidentally drilled a core 55 miles south of the intended site, crossing from Cascadia into the San Andreas system. This “fault” produced an unusual sediment layer – a layer that has coarse grains on top and fine grains on the bottom, and is essentially upside down compared to typical sediments.

Subsequent analysis revealed that the finer underlying layer likely came from the Great Cascadia Earthquake, and the coarser layer from the near-instantaneous San Andreas rupture. This was the first hint that the two rifts could have been moving side by side. Years later, after hundreds of cores and countless hours of data analysis, the team confirmed that this dual pattern had been repeated throughout history.

Echoes of recent centuries

The sediment record captures even recent events. The 1906 San Francisco earthquake, the 1992 Cape Mendocino earthquake, and the 1700 Cascadia megathrust event all left visible marks on either side of the triple intersection. The 1700 earthquake – which also generated the tsunami that struck Japan – stands out as one of the clearest examples of the system's combined seismic signature.

CT scan images of turbidites in deep-sea sediment cores. (Credit: Goldfinger, et al.)

In some cases, the time interval between the coupled Cascadia and San Andreas earthquakes may be only minutes or hours, Goldfinger said. This is close enough for emergency planners to pay attention. “We can expect that an earthquake on one fault alone would exhaust the entire country's resources to respond to it,” he said. “And if they both exploded together, San Francisco, Portland, Seattle and Vancouver would all likely be in a state of emergency in a compressed time frame.”

Could these binaries have formed by chance, perhaps from underwater landslides or random shifts in sediments? Researchers don't think so. When the Cascadia and San Andreas events occur far apart in time, the cores appear single, clean layers. Binaries appear only when the tremors of the two systems coincide closely. Even more telling is that the total number of layers near the triple junction is not higher than expected, meaning that these are not unrelated events accumulating, but coupled signals of connected systems.

Rethinking the seismic future of the West Coast

The discovery could reshape how scientists assess earthquake risk from California to British Columbia. If the Cascadia Subduction Zone and the San Andreas Fault can act in concert, seismic models must take into account the possibility of coupled behavior. This could mean an increased risk of cascading disasters in the short term, as one system equips another within decades or even days.

Representative core and benthic comparison of two core sites in the Cascadia subduction zone. (Credit: Goldfinger, et al.)

However, Goldfinger cautions that synchronization does not equal predictability. These interconnected events appear to come and go over time, following a geological rhythm spanning thousands of years. “It's not that they're always paired,” he said. “But when that happens, it can produce cascading great earthquakes that change everything.”

Practical implications of the research

Understanding that two major fault systems may affect each other has far-reaching consequences for public safety and planning. If the large Cascadia earthquake could rupture the northern San Andreas — or vice versa — emergency preparedness plans for the entire West Coast may need to be updated.

The discovery also provides new insight into how the Earth's crust stores and releases pressure. By learning how energy is transferred between vastly different tectonic systems, researchers can improve long-term hazard predictions and better estimate the potential reach of future large earthquakes.

More broadly, this study reminds scientists and citizens alike that the planet's surface operates as a single interconnected machine. One mega-event may extend across hundreds of miles — or decades — affecting when and where the next major earthquake strikes.

The research results are available online in the journal Geosphere.

Related stories

These kind of feel-good stories? Get the Bright Side of News newsletter.

What Are The Main Benefits Of Comparing Car Insurance Quotes Online

LOS ANGELES, CA / ACCESSWIRE / June 24, 2020, / Compare-autoinsurance.Org has launched a new blog post that presents the main benefits of comparing multiple car insurance quotes. For more info and free online quotes, please visit https://compare-autoinsurance.Org/the-advantages-of-comparing-prices-with-car-insurance-quotes-online/ The modern society has numerous technological advantages. One important advantage is the speed at which information is sent and received. With the help of the internet, the shopping habits of many persons have drastically changed. The car insurance industry hasn't remained untouched by these changes. On the internet, drivers can compare insurance prices and find out which sellers have the best offers. View photos The advantages of comparing online car insurance quotes are the following: Online quotes can be obtained from anywhere and at any time. Unlike physical insurance agencies, websites don't have a specific schedule and they are available at any time. Drivers that have busy working schedules, can compare quotes from anywhere and at any time, even at midnight. Multiple choices. Almost all insurance providers, no matter if they are well-known brands or just local insurers, have an online presence. Online quotes will allow policyholders the chance to discover multiple insurance companies and check their prices. Drivers are no longer required to get quotes from just a few known insurance companies. Also, local and regional insurers can provide lower insurance rates for the same services. Accurate insurance estimates. Online quotes can only be accurate if the customers provide accurate and real info about their car models and driving history. Lying about past driving incidents can make the price estimates to be lower, but when dealing with an insurance company lying to them is useless. Usually, insurance companies will do research about a potential customer before granting him coverage. Online quotes can be sorted easily. Although drivers are recommended to not choose a policy just based on its price, drivers can easily sort quotes by insurance price. Using brokerage websites will allow drivers to get quotes from multiple insurers, thus making the comparison faster and easier. For additional info, money-saving tips, and free car insurance quotes, visit https://compare-autoinsurance.Org/ Compare-autoinsurance.Org is an online provider of life, home, health, and auto insurance quotes. This website is unique because it does not simply stick to one kind of insurance provider, but brings the clients the best deals from many different online insurance carriers. In this way, clients have access to offers from multiple carriers all in one place: this website. On this site, customers have access to quotes for insurance plans from various agencies, such as local or nationwide agencies, brand names insurance companies, etc. "Online quotes can easily help drivers obtain better car insurance deals. All they have to do is to complete an online form with accurate and real info, then compare prices", said Russell Rabichev, Marketing Director of Internet Marketing Company. CONTACT: Company Name: Internet Marketing CompanyPerson for contact Name: Gurgu CPhone Number: (818) 359-3898Email: [email protected]: https://compare-autoinsurance.Org/ SOURCE: Compare-autoinsurance.Org View source version on accesswire.Com:https://www.Accesswire.Com/595055/What-Are-The-Main-Benefits-Of-Comparing-Car-Insurance-Quotes-Online View photos