Although the common belief among scientists is that Earth's tectonic plates remain strong when they slide under another plate in a process called subduction, a new study from researchers at the University of Southampton found that this belief may not be universal, according to a press release. The scientists examined Earth's largest flat slab, the Nazca Plate which is located underneath Peru and might possess fairly weak structural characteristics and deform easily.
"The process of consuming old seafloor at subduction zones, where great slabs of oceanic material are swallowed up, drives circulation in the Earth's interior and keeps the planet going strong," said Caroline Eakin, lead author of the study.
"One of the most crucial but least known aspects of this process is the strength and behavior of oceanic slabs once they sink below the Earth's surface," she said. "Our findings provide some of the first direct evidence that subducted slabs are not only weaker and softer than conventionally envisioned, but also that we can peer inside the slab and directly witness their behavior as they sink."
Eakin and her team made the findings by studying the speed at which seismic waves travel in various directions through identical material, which is referred to as seismic anisotropy. They found that the original olivine structure of the Nazca plate had been replaced by a new alignment that was in an opposite orientation, suggesting that the interior of the plate became deformed during the subduction process.
"The best way to explain this observation is that the slab's interior must have been stretched or deformed during subduction, said Eakin. "This means that slabs are weak enough to deform internally in the upper mantle over time."