Pacific Plate Tear: A Geological Study from Japan to NZ

The Pacific plate is the largest tectonic plate on Earth, covering most of the Pacific Ocean floor and stretching from the west coast of North America to Japan, New Zealand and Australia. It is also part of the Pacific Ring of Fire, a zone of intense seismic and volcanic activity. But what is happening to this massive plate as it moves over the Earth’s mantle?


A new study by researchers from the University of Toronto reveals that the Pacific plate is not as rigid and pristine as previously thought. Instead, it is scored by large undersea faults that are pulling it apart in various locations, far from the plate boundaries. These faults are hundreds of kilometres long and thousands of metres deep, and they are caused by enormous forces that tug at the plate edges.

The researchers used existing data on four oceanic plateaus in the western Pacific Ocean: the Ontong Java, Shatsky, Hess and Manihiki plateaus. These are elevated regions of the seafloor that are thicker than the surrounding oceanic crust. The researchers fed the data to a supercomputer, which compared it with information collected in studies done in the 1970s and 80s.

Results of Pacific Plate Tear

The results showed that the plateaus are weaker than expected, and they are deforming under stress. The faults tend to run parallel to the nearest plate boundary, where subduction occurs. Subduction is the process where one plate slides under another and sinks into the mantle. This creates a downward pull on the plate edge, which in turn affects the interior of the plate.

“It was thought that because the sub-oceanic plateaus are thicker, they should be stronger. But our models and seismic data show it’s actually the opposite: the plateaus are weaker,” said Erkan Gün, a post-doctoral researcher in the department of Earth Sciences in the Faculty of Arts & Sciences.


The study also identified new points at which the Pacific plate is being pulled down into the mantle, which could have implications for understanding how plates recycle and how continents form.

“A new finding like this overturns what we’ve understood and taught about the active Earth. And it shows that there are still radical mysteries about even the grand operation of our evolving planet,” said Russell Pysklywec, a professor in the department of Earth sciences.

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