Nanoscale observations simplify how scientists describe earthquake motion — ScienceDaily

Nanoscale observations simplify how scientists describe earthquake motion — ScienceDaily

Using single calcite crystals with different surface roughness allows engineers to simplify the complex physics that describe fault movement. In a new study from the University of Illinois at Urbana-Champaign, researchers show how this simplification can lead to better earthquake prediction.

Scientists describe the behavior of faults using models based on observational studies that account for the friction coefficients of rocks and minerals. These rate and state equations calculate the strength of the fault, which has implications for earthquake strength and frequency. However, applying these empirical models to earthquake prediction is not practical due to the number of unique variables that must be considered for each fault, including the effect of water.

The study, led by civil and environmental engineering professor Rosa Espinosa-Martzal, looked at the relationship between friction and the surface roughness of calcite — one of the most common rock-forming minerals in the Earth’s crust — to formulate a more theoretical approach to determining the laws of speed and status.

The findings are published in Proceedings of the National Academy of Sciences.

“Our goal is to study the nanoscale processes that can trigger fault movement,” said Binxin Fu, a CEE graduate student and first author of the study. “The processes we study at the nanoscale are less complex than the processes at the macroscale. We therefore aim to use microscopic observations to bridge the gap between the nanoscale and macroscale worlds to describe fault behavior using less complexity.”

The roughness of a mineral crystal depends primarily on its atomic structure. However, the researchers said that the rocks in the contact zones are scraped, dissolved and heated as they rub against each other, which also affects their nanoscale texture.

To test how nanoscale mineral roughness can affect defect behavior, the team prepared atomically smooth and rough calcite crystals in dry and wet environments to simulate dry rocks and those containing pore water. Atomic force microscopy measures friction by sliding a small, pressure-mounted silicon tip across different crystal surfaces exposed to simulated fault zone conditions: wet surface and smooth calcite; wet surface and rough calcite; dry surface and smooth calcite; and dry surface with rough calcite.

“Friction can increase or decrease with sliding speed depending on the types of minerals and the environment,” Espinosa-Marzal said. “We found that in calcite, friction generally increases with sliding speed on rougher mineral surfaces – and even more so in the presence of water. By using data from such a common mineral type and a limited number of contact scenarios, we reduce the complexity of the analysis. and provides a fundamental understanding of the rate and state equations.”

The team compared their experimental results with studies of natural settings with calcite-bearing rocks at shallow levels of the Earth’s crust.

“Our results agree with a recent study showing that water reduces fracture toughness compared to dry conditions,” said Espinosa-Marzal. “Our findings are also consistent with another study showing that low-frequency earthquakes tend to occur along wet faults, suggesting that reduced friction – caused by water – may be a mechanism for slow earthquakes in some environments. “

This advance could help seismologists redefine rate and state laws to determine where stress builds up in the Earth’s crust—and provide clues to where and when future earthquakes might occur.

The team acknowledges that there are still many other factors to consider, including temperature and the influence of other common crustal minerals such as quartz and mica. The researchers plan to incorporate these variables into future models.

The National Science Foundation supported this study.

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Materials provided by University of Illinois at Urbana-Champaign, News Bureau. Original written by Lois Yoksoulian. Note: Content may be edited for style and length.

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