Pacific Plate that Dominates 'Ring of Fire' Not Nearly as Rigid as Previously Thought

It turns out that the tectonic plate located in the Pacific that dominates the "Ring of Fire" is not nearly as rigid as previously thought. Scientists have found that cooling is causing some sections of the Pacific plate to contract horizontally at far faster rates than others, and causes the plate to deform.

The tectonic plates that cover Earth's surface, including those on land and near the seafloor, are in constant motion. They slowly surf across the viscous mantle below. Over time, these plates rub against one another, creating mountains, trenches, and other features. Because movements only occur in a scale of inches per year, though, it's hard to see changes. That's why the deformations in the Pacific plate have gone unnoticed for so long.

"The central assumption in plate tectonics is that the plates are rigid, but the studies that my colleagues and I have been doing for the past few decades show that this central assumption is merely an approximation-that is, the plates are not rigid," said Richard Gordon, one of the researchers, in a news release. "Our latest contribution is to specify or predict the nature and rate of deformation over the entire Pacific plate."

The researchers first determined how much contractions would, on average, strain the horizontal surface of the plate. Then they divided the Pacific plate into a grid and calculated the strain on each of the nearly 198,000 squares based on their age.

In this case, the researchers found that the Pacific plate is pulling away from the North American plate at about 2 millimeters per year. This is far more than the rigid-plate theory would account for. Overall, the plate is moving northwest at about 50 millimeters per year.

"The big picture is that we now have, subject to experimental and observational tests, the first realistic, quantitative estimate of how the biggest oceanic plate departs from that rigid-plate assumption," said Gordon.

The findings are published in the journal Geology.