Cascadia subduction zone shows signs of tectonic fragmentation

Geologists have observed the progressive fragmentation of the Cascadia subduction zone off the coast of the Pacific Northwest. A study published in Science Advances reveals that the Juan de Fuca and Explorer plates, which slide beneath the North American plate near Vancouver Island, are undergoing significant structural breakdown.

Using data from the 2021 CASIE21 seismic imaging experiment, researchers identified a 75-kilometer-long fracture within the oceanic plate. The study, funded by the National Science Foundation, utilized high-resolution seismic reflection and sound waves recorded by a 15-kilometer underwater cable to map the seafloor. Findings indicate a vertical displacement of approximately five kilometers in certain sections.

Lead author Brandon Shuck, a geologist at Louisiana State University, noted that the fracture is actively breaking the plate, though the detachment is not yet complete. Seismic data shows a pattern of varying activity: some areas along the fracture remain seismically active, while others are unusually quiet, suggesting that certain plate fragments have already separated. This indicates that subduction zones may not disappear through a single catastrophic event, but rather through a gradual process of fragmentation into microplates.