Earth’s Ancient, Hidden “Scars” Could Produce Earthquakes in Unlikely Locations

June 10, 2016 | Joanne Kennell

Utah from above
Photo credit: edward stojakovic/flickr (CC BY 2.0)

These scars can come back to life.

A new study is challenging the view that earthquakes, and the formation of mountains, can only occur due to the interactions between plate tectonic boundaries. Using a super-computer to model Earth’s crust and upper mantle, the researchers propose that ancient geological events may have left deep “scars” that can sometimes come back to life.

A team of researchers from the University of Toronto (U of T) and the University of Aberdeen (UOA) have created models of the Earth’s crust and upper-mantle using U of T's SciNet — Canada's most powerful computer. However, they also incorporated some deep scars.

According to their results, former plate boundaries may stay hidden deep beneath Earth’s surface for millions of years. What’s more, these old structures, located far from existing plate boundaries, may result in structural changes on Earth’s surface.

"This is a potentially major revision to the fundamental idea of plate tectonics," said lead author Philip Heron, a postdoctoral fellow in Russell Pysklywec's research group in U of T's Department of Earth Sciences, in a U of T news release.

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Heron and Pysklywec, along with UOA geologist Randell Stephenson, propose that a new “perennial plate tectonic map” of Earth should be used to illustrate how ancient geological activity could spawn present-day events.

Map of tectonic plates

The proposed perennial plate tectonic map. Present-day plate boundaries (white lines), with hidden ancient plate boundaries (yellow lines). Image credit: Russell Pysklywec, Philip Heron, Randell Stephenson

"It's based on the familiar global tectonic map that is taught starting in elementary school," explained Pysklywec. "What our models redefine and show on the map are dormant, hidden, ancient plate boundaries."

Using models to create an evolving “virtual Earth,” the team was able to show that different parts of the upper mantle, which is located below the crust and is predominantly solid but acts as a viscous fluid on a geological timescale, can control the folding, breaking, or flowing of the planet’s crust within tectonic plates when experiencing compression. This folding, breaking, or flowing can result in the formation of mountains, and even produce seismic activity.

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"Most of the really big plate tectonic activity happens on the plate boundaries, like when India rammed into Asia to create the Himalayas or how the Atlantic opened to split North America from Europe," said Heron. "But there are lots of things we couldn't explain, like seismic activity and mountain-building away from plate boundaries in continent interiors."

Another theory to explain the unusual seismic activity occurring in the Southeast US — also located in the middle of a plate — is that pieces of the mantle under the region are periodically breaking off and sinking down into the Earth, thinning and weakening the remaining plate. This makes the region more prone to earthquakes.

This new study offers another possible explanation.

The researchers believe that their simulations demonstrate that these unexplained mantle anomalies are generated through ancient plate tectonic processes. These scars can remain hidden for millions of years, far away from current plate boundaries, but will once again reveal themselves after a reactivation. However, what spurs the emergence is currently not known.

"Plate tectonics is really the cornerstone of all geoscience," said Pysklywec. "Ultimately, this information could even lead to ways to help better predict how and when earthquakes happen. It's a key building block."

The paper, "Lasting mantle scars lead to perennial plate tectonics," will be published today (June 10) in the journal Nature Communications.

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