A new study suggests tectonic plates are weaker than previously thought.

The findings, shared this week in the journal Science Advances, explain the discrepancy between rock strength tests in the lab and real world observations of tectonic rocks.

Lab experiments suggested tectonic plates -- which are composed of olivine-rich rocks -- were surprisingly strong, but the test results didn't always jive with what scientists were seeing and measuring in the natural world.

The discrepancy has long limited scientists' understanding of how tectonic plates break and form boundaries.

"Furthermore, the estimates of rock strength from laboratory experiments exhibit considerable variability, reducing confidence in using experiments to estimate rock properties," Lars Hansen, an earth scientists at Oxford University, said in a news release.

A new analysis method called nanoindentation helped researchers get a more accurate measurement of the strength of tectonic rocks. The results of the new analysis showed olivine-rich rocks can appear strong at smaller scales but break more easily at larger scales.

"Variability among previous estimates of strength is a result of a special length-scale within the rocks -- that is, the strength depends on the volume of material being tested," Hansen explained. "To determine this we used nanoindentation experiments in which a microscopic diamond stylus is pressed into the surface of an olivine crystal. These experiments reveal that the strength of the crystal depends on the size of the indentation."

In the lab, scientists have mostly tested synthetic rocks with smaller crystals than are found in nature. As a result, many tests overestimated the strength of olivine-rich rocks.

Researchers hope the new findings will help them better understand a variety of tectonic phenomena.

"For instance, we now know that the evolution of stresses on earthquake-generating faults likely depends on the size of the individual crystals that make up the rocks involved," Hansen said. "In addition, flexing of plates under the weight of volcanoes or large ice sheets, a process intimately linked to sea level on Earth, will also ultimately depend on crystal size."

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Measuring a crucial mineral in the mantle
Newark DE (SPX) Sep 15, 2017
University of Delaware professor Jessica Warren and colleagues from Stanford University, Oxford University and University of Pennsylvania, reported new data that material size-effects matter in plate tectonics. Plate tectonics, the way the Earth's plates move apart and come back together, has been used since the 1960s to explain the location of volcanoes and earthquakes. The study (link he ... read more

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