Earth is tearing apart beneath the Pacific Northwest

Researchers used dense earthquake catalogs and high-resolution seismic reflection imaging from the 2021 Cascadia Seismic Imaging Experiment to produce detailed images of the Juan de Fuca and Explorer slabs beneath Vancouver Island and found the subduction system actively tearing apart. The seismic streamer data reveal large faults and fractures cutting the sinking plate, including a dramatic fault with roughly a 5-kilometer offset and a roughly 75-kilometer-long tear where parts still produce earthquakes while adjacent segments are seismically quiet. Those contrasts indicate sections have already detached and a damaged slab is fragmenting into smaller blocks as it continues to sink.

The observations demonstrate that subduction termination can proceed episodically, with transform faults slicing the plate into microplates and creating slab windows that let hot mantle rise and change magma production. That piecewise decay explains ancient fossil plate fragments and irregular volcanic sequences such as remnants of the Farallon system. For Cascadia, the newly imaged tears could influence how future ruptures propagate, so integrating these structures into earthquake models will refine understanding of rupture behavior, even though the large-scale hazard remains governed by processes unfolding over millions of years.