Seismic Activity on North America’s West Coast

The western coast of North America is a geologically active region where tectonic plates collide and move beneath one another, causing significant earthquakes throughout history. Recent research has revealed that some of these seismic events have occurred simultaneously along two major faults in the area: the San Andreas Fault and the Cascadia Subduction Zone.

Recent Research on Seismic Activity

A team of researchers analyzed a large amount of seabed sediment from the area where these faults converge off the coast of Northern California. The findings, recently published in the journal Geosphere, indicate that the fault systems have produced several simultaneous earthquakes over the past 3,000 years.

Marine geologist Chris Goldfinger from Oregon State University describes the process as similar to tuning an analog radio, where oscillators synchronize to transform received signals. When these faults synchronize, one can trigger the other, causing double earthquakes.

The Cascadia Subduction Zone and the San Andreas Fault

The Cascadia Subduction Zone, where the Juan de Fuca and Gorda plates slide beneath the North American plate, extends from Vancouver Island to Northern California, meeting the San Andreas Fault. This fault runs southward for 750 miles along the boundary where the North American and Pacific plates slide past each other.

Since 1999, Goldfinger and his team have been drilling into the seabed at the plate junction known as the Mendocino Triple Junction to collect samples that provide a cross-section of the sediments formed there. In the new study, more than 130 sediment samples recording about 3,000 years of geological history were examined.

The Role of Sediments in Understanding Earthquakes

Many samples contain sedimentary layers known as turbidites, which form as a result of underwater landslides that move large amounts of material around the ocean floor. Earthquakes cause many of these slides, making turbidite layers a useful tool for identifying past seismic events.

Most turbidites have coarse sediment layers at the bottom and finer ones on top, but samples from the Mendocino Triple Junction appear inverted with sand on top. Goldfinger realized the samples contained stacked turbidites, providing evidence of separate earthquakes occurring in quick succession.

Future Challenges and Earthquake Planning

If the fault systems produce large earthquakes in rapid succession, it could lead to significant disasters along the west coast of North America. Goldfinger hopes the new study will contribute to seismic hazard planning for communities near both systems.

Although the Cascadia and San Andreas systems have been linked throughout history, there is some variation in timing between successive earthquakes. Researchers point to the need for further studies to understand how one earthquake affects another.

Conclusion

The recent discoveries about seismic activity on the west coast of North America are an important step in understanding how earthquakes synchronize across the two major fault systems. The study highlights the urgent need for better seismic risk planning and preparedness for potential future disasters. Understanding how these faults interact can play a crucial role in improving earthquake response and recovery strategies in the region.