Pacific Northwest Subduction Zone Is Tearing Apart

Scientists have observed a subduction zone actively breaking apart for the first time. The Juan de Fuca plate is fragmenting as it sinks beneath North America. This process occurs off the coast of Vancouver Island in the Cascadia region. Researchers used advanced seismic imaging to make this discovery.

Subduction zones are areas where one tectonic plate slides beneath another. These zones are responsible for significant geological events. They cause earthquakes and volcanic eruptions. This new finding explains how these powerful systems evolve and eventually cease.

The study, published in *Science Advances*, indicates that the plate is tearing piece by piece. It is not collapsing all at once. This gradual breakdown creates smaller microplates and new boundaries. This process is called episodic or piecewise termination. It helps explain ancient plate fragments found elsewhere on Earth.

Data came from the 2021 Cascadia Seismic Imaging Experiment (CASIE21). Researchers used seismic reflection imaging and earthquake records. They sent sound waves into the seafloor. Underwater sensors captured the echoes. This method provided detailed images of faults and fractures deep beneath the ocean floor.

These images show sections of the plate breaking apart. One major fault shows the plate has dropped by about five kilometers. Earthquake data supports this observation. Some areas along a 75-kilometer-long tear still produce earthquakes. Other areas are unusually quiet, suggesting parts of the plate have already separated.

This research offers insights into how subduction zones end. It also raises new questions about earthquake risks in the Pacific Northwest. The findings do not change the overall risk of large earthquakes and tsunamis in the Cascadia region. However, incorporating these details will improve seismic hazard models.