Scientists simulate Earth's middle crust to understand earthquakes

September 28, 2015

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), research unit of the Jackson School of Geosciences, spearheaded the discovery. The study was published in the September 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 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.

Previously, nearly all research into such movements of the Earth's crusts was done by measuring tectonic movement using GPS readings and linking these findings with friction laws. Those observations did not address how rock behaves when it softens under heat and pressure.

"It is not really clear how slow-slip events interact with earthquakes, whether they can trigger earthquakes or it's the other way around - that earthquakes trigger slow-slip events," said Jacqueline Reber, the study's lead author who performed this research as postdoctoral fellow at UTIG, and who is now an assistant professor at Iowa State University.

The research also adds insight into middle crust strain transients, temporary stress on surrounding rock that's caused by tectonic motion.

"By understanding the mechanics of strain transients a little bit better, we eventually hope to get better insight into how they relate to big, catastrophic earthquakes."

Unlike slow slips events, earthquakes - or stick-slip events - occur when surfaces quickly alternate between sticking to each other and sliding over each other.

"While earlier studies focused mostly on frictional behavior as an explanation for strain transients we focus in our work on the impact of rheology (how a material flows under stress), especially when it is semi-brittle," said Reber.

The semi-brittle middle crust can be compared to a candy bar made of nuts and caramel. The nuts represent the brittle rock. The caramel represents the ductile rock.

Researchers exposed Carbopol, in which the ratio between brittle and ductile parts determines how much stress it can take before being permanently deformed or breaking, to forces created by a simple spring-powered shearing apparatus. Lower yield stress induced the Carbonol to imitate hotter, more viscous rock from deeper in the Earth's crust by making it more ductile; at higher yield stress it imitated cooler, more brittle rock.

The tests showed viscous deformation and constant creep movement at lower yield stress and slip-stick 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.
-end-
The research team included Reber, Luc L. Lavier, an associate professor in the Jackson School's Department of Geological Sciences and a UTIG research scientist, and Nicholas W. Hayman, a UTIG research scientist.

Funding came from UTIG and Petrobras, a Brazilian energy corporation.

University of Texas at Austin

Related Stress Articles from Brightsurf:

Stress-free gel
Researchers at The University of Tokyo studied a new mechanism of gelation using colloidal particles.

Early life stress is associated with youth-onset depression for some types of stress but not others
Examining the association between eight different types of early life stress (ELS) and youth-onset depression, a study in JAACAP, published by Elsevier, reports that individuals exposed to ELS were more likely to develop a major depressive disorder (MDD) in childhood or adolescence than individuals who had not been exposed to ELS.

Red light for stress
Researchers from the Institute of Industrial Science at The University of Tokyo have created a biphasic luminescent material that changes color when exposed to mechanical stress.

How do our cells respond to stress?
Molecular biologists reverse-engineer a complex cellular structure that is associated with neurodegenerative diseases such as ALS

How stress remodels the brain
Stress restructures the brain by halting the production of crucial ion channel proteins, according to research in mice recently published in JNeurosci.

Why stress doesn't always cause depression
Rats susceptible to anhedonia, a core symptom of depression, possess more serotonin neurons after being exposed to chronic stress, but the effect can be reversed through amygdala activation, according to new research in JNeurosci.

How plants handle stress
Plants get stressed too. Drought or too much salt disrupt their physiology.

Stress in the powerhouse of the cell
University of Freiburg researchers discover a new principle -- how cells protect themselves from mitochondrial defects.

Measuring stress around cells
Tissues and organs in the human body are shaped through forces generated by cells, that push and pull, to ''sculpt'' biological structures.

Cellular stress at the movies
For the first time, biological imaging experts have used a custom fluorescence microscope and a novel antibody tagging tool to watch living cells undergoing stress.

Read More: Stress News and Stress Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.