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Scientists Make Middle Crust Model

Researchers have for the first time been able to measure a material’s resistance to fracturing from various types of tectonic motions in the Earth’s middle crust, a discovery that may lead to better understanding of how large earthquakes and slower-moving events interact.

The University of Texas Institute for Geophysics (UTIG), spearheaded the discovery, which was published in the September 2015 edition of Nature Geoscience.

Scientists conducted the research using Carbopol, a gel-like substance that can simulate the characteristics of rock formations in the Earth’s middle crust because it is simultaneously brittle and malleable.

Researchers performed shear tests on the Carbopol, where a portion of the material is pulled in one direction and a portion is pulled in the opposite direction. This is similar to what happens to rock formations in the middle crust during earthquakes or slow-slip events, a type of tectonic movement that resembles an earthquake but happens over a much longer period of time.

The tests showed viscous deformation and constant creep movement at lower yield stress and slip-stick, or earthquake-like, behavior at higher yield stress. This highlights the importance of a material’s often complex properties for determining the manner and speed it will respond to stress.

Jacqueline Reber, the study’s lead author, performed the research as a postdoctoral fellow at UTIG and is now an assistant professor at Iowa State University. The research team included Luc L. Lavier, of the Jackson School’s Department of Geological Sciences and UTIG, and Nicholas W. Hayman, a UTIG research scientist. Funding came from UTIG and Petrobras, a Brazilian energy corporation.