Scientists have captured an unusually detailed view of a major tectonic system beneath the Pacific Northwest beginning to come apart. The discovery, reported in Science Advances, shows a subduction zone actively breaking into pieces. Subduction zones form where one tectonic plate is forced beneath another and pushed deep into Earth.
They are responsible for some of the planet's largest earthquakes, powerful volcanic eruptions, and long term changes to continents and ocean basins. Until now, however, scientists have had few opportunities to see clearly how one of these enormous systems reaches the end of its life. Subduction is one of the main processes that continually reshapes Earth's surface.
As an oceanic plate sinks beneath another plate, material from the crust is carried downward toward the mantle, the hot layer beneath Earth's crust. These systems can remain active for millions of years, but they cannot continue indefinitely. Otherwise, continents would eventually pile into one another, oceans would disappear, and much of Earth's geological history would be erased.
That leaves geologists with a fundamental question: what actually causes a mature subduction zone to stop? "Getting a subduction zone started is like trying to push a train uphill -- it takes a huge effort," said Brandon Shuck, a geologist at Louisiana State University and lead author of the study. "But once it's moving, it's like the train is racing downhill, impossible to stop.
Ending it requires something dramatic -- basically, a train wreck." Scientists may now be watching that process unfold beneath Cascadia. A Tectonic Plate Breaking Apart Beneath Cascadia Off Vancouver Island, the Juan de Fuca and Explorer plates are slowly being forced beneath the North American plate. This area is part of the Cascadia subduction zone, a vast tectonic boundary stretching along the Pacific Northwest.
Researchers combined detailed earthquake records with seismic reflection imaging to look deep beneath the seafloor. The technique works somewhat like medical ultrasound. Scientists send sound waves into Earth and measure how those waves bounce back from different underground structures.
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