Scientists have captured the clearest view yet of a section of Earth crust beneath the Pacific Ocean off Canada’s coast as it begins to break into smaller pieces. The finding shows part of the Cascadia tectonic system fragmenting deep below the seabed, in a process that unfolds over millions of years rather than in a sudden shift.
Brandon Shuck, one of the researchers, said it was the first time the team had a clear image of a subduction zone in the process of disappearing, comparing it to a train that slowly derails wagon by wagon. The work was published in Science Advances after an international group of scientists used deep seismic imaging and earthquake records to reconstruct structures hidden several kilometers below the ocean floor.
The study focused on the northwest Pacific, where the Juan de Fuca and Explorer oceanic plates interact with the North American plate. That type of boundary is called a subduction zone, where one tectonic plate slips beneath another and sinks into the mantle. Because these zones are tied to some of the world’s largest earthquakes and volcanoes, any fresh look at how they evolve matters well beyond the map line itself.
The images show a structure about 75 kilometers long linked to the fragmentation, and the data also point to sectors where seismic activity differs sharply from one another. Those differences are what allow scientists to see which parts remain connected and which are moving toward full separation. Some segments appear to be edging closer to complete detachment, but not all of the system has broken away.
That is the part that keeps the story from sounding more dramatic than the evidence allows. The Earth crust there is changing, but it is doing so on geological time, not human time. Shuck said one region has not detached completely yet, but is close to doing so, which leaves the bigger question not whether the breakup is happening, but how much of Cascadia is still holding together and how long that hidden transition will continue before the next major change can be measured.
