Scientists have captured the first clear images of a subduction zone breaking apart beneath the Pacific Northwest. The Juan de Fuca plate is splitting into fragments as it sinks under the North American plate. The findings, from a 2021 seismic experiment, reveal a gradual tearing process.
Researchers using advanced seismic imaging have watched the Juan de Fuca plate tear piece by piece off the coast of Vancouver Island in the Cascadia region. The plate, sliding beneath North America, shows large faults and fractures, including one where it has dropped about five kilometers. Data from earthquakes reveal active tears along a 75-kilometer stretch, with quiet gaps indicating separated sections no longer produce quakes, as Brandon Shuck, lead author and assistant professor at Louisiana State University, explained: “Once a piece has completely broken off, it no longer produces earthquakes because the rocks aren't stuck together anymore.” Shuck conducted the work as a postdoctoral fellow at Lamont-Doherty Earth Observatory, part of Columbia Climate School, and likened the process to “a train slowly derailing, one car at a time.”The observations come from the 2021 Cascadia Seismic Imaging Experiment (CASIE21), aboard the research vessel Marcus G. Langseth. Led by Suzanne Carbotte with co-author Anne Bécel, the team deployed a 15-kilometer array of underwater sensors to create ultrasound-like images of the seafloor. “This is the first time we have a clear picture of a subduction zone caught in the act of dying,” Shuck said. Carbotte added that the images clarify how lighter plate sections can stall subduction, aiding understanding of tectonic life cycles.The study, published in Science Advances, describes “episodic” or “piecewise” termination, where the plate loses downward pull over millions of years. This process explains ancient plate fragments, such as remnants of the Farallon plate off Baja California. While the tears raise questions about earthquake propagation in Cascadia, officials note they do not significantly change the region's overall risk of large quakes and tsunamis. The research is supported by the National Science Foundation.
