Study Examines Fluid Migration in Cascadia Subduction Zone

A new study examined fluid movement inside the Cascadia Subduction Zone, a 700-mile fault that runs from Northern California to British Columbia. The zone marks the boundary where the Juan de Fuca Plate slides beneath the North American Plate at roughly four centimeters per year.

Scientists at the University of Washington used data from the Regional Cabled Array, an underwater network of more than 550 miles of cables and instruments, to detect seismic noise and map fluid pathways.

The study found that episodic tremor and slip events create channels that allow hot fluid to migrate toward the seafloor. Researchers stated that this fluid movement can weaken the fault and increase stress in the northern section. Maleen Kidiwela, lead author and postdoctoral researcher, said measurements showed strain building in the northern part of the zone.

The same data indicated that future ruptures there could reach higher magnitudes than those expected in the central section.

Earthquake and Tsunami Risk The U.S.

Geological Survey reported a 10 to 15 percent chance of a magnitude-9 earthquake occurring in the Pacific Northwest within the coming decades. The study noted that fluid migration could influence the size of any eventual event. Kidiwela added that earthquakes would occur offshore and might generate tsunamis.

Evidence from a separate 2021 imaging project showed a portion of the Juan de Fuca Plate tearing, which researchers described as a subduction zone in the process of dying. The National Science Foundation awarded a $15 million grant in 2023 to expand offshore monitoring and early-warning systems for the region.