Study leads to new scale of earthquake understanding

[Judi Lynn]

Source: Xinhua| 2018-06-29 05:00:29|Editor: Mu Xuequan

CHICAGO, June 28 (Xinhua) -- Nanoscale knowledge of the relationships between water, friction and mineral chemistry could lead to a better understanding of earthquake dynamics, a study of the University of Illinois (UI) shows.

The study focuses on calcite-rich rocks in the presence of brine, naturally occurring salty groundwater, along fault surfaces. The rock surfaces that slide past each other along faults are not smooth. The researchers zoomed in on the naturally occurring tiny imperfections or unevenness on rocks' surfaces, called asperities, at which friction and wear originate when the two surfaces slide past each other.

For the experiments, the researchers submerged calcite crystals in brine solutions at various concentrations and subjected them to different pressures to simulate a natural fault setting. Once the crystals were in equilibrium with the solution, they used an atomic force microscope to drag a tiny arm with a silicon tip across the crystal to measure changes in friction.

In most of the experiments, the researchers first found what they expected: As the pressure applied on the crystals increased, it became more difficult to drag the tip across the crystal's surface. However, when they increased pressure to a certain point and the tip was moved slowly enough, the tip began to slide more easily across the crystal.

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