How to change the fault lines in the kitchen sink

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Video: Animation of a plate displacement experiment showing the evolution of the fault system. Show more

Credit: UMass Amherst

Amherst, MA – In a new paper recently published in the Journal of Geology, researchers at the University of Massachusetts Amherst reveal a physical model that produces an unprecedented high-resolution look at the slip rates of faults, which determine the likelihood of earthquakes.

When most of us picture a fault line, we imagine a giant crack in the Earth where two tectonic plates collide with each other. When geologists think of faults, they see a branching system made up of thousands of individual faults. “The more you look closely, the more you find, and when you look in detail, the picture becomes very complex,” says Michael Cook, one of the paper’s co-authors and a professor of Earth sciences at UMass Amherst.

Such complexity makes it difficult to understand precisely what is happening in any particular place in the system — let alone predict when and where an earthquake will occur. To darken the picture even more, the vast majority of individual defects are buried under feet of dirt or obscured by plants, and therefore not directly observable. Finally, fault systems evolve over thousands, tens of thousands, or even millions of years. Therefore, geologists have traditionally established generalized slip rates for entire fault systems and broadly theorized about how fault systems evolve.

In a new study, the authors used a physical model, “about the size of a kitchen sink,” says Hanna Elston, lead author and a graduate student in Earth sciences at UMass Amherst, and filled it with carefully composed kaolin clay, “about the consistency of Greek yogurt,” behaving Like the crust of the earth. At the bottom of the model there are two plates that can be moved neatly. Next, Elston and her colleagues carefully cut the clay to form a crack, and over the course of four hours, which simulates a million years, moved the 12cm plates, all while taking pictures with an array of overhead cameras, which they could then analyze to reveal their typical slip rates and fault mechanisms.

The precision of the first-of-its-kind technique developed by Elston and her co-authors allows slip rates to be tracked at specific locations along faults, with unprecedented accuracy, which can then provide a record that researchers can directly compare in the field. Studies to estimate the slip rate at any given point along the fault.

Not only does the model work in ways that reflect real-life errors, but it has allowed Elston and her colleagues, including Cook and Alex Hatem, now at the USGS, to observe two different phenomena that no one had seen before. First, the model shows that slip rates can change at a particular location on the fault as that fault develops. Second, the team showed that slip rates are interactive: the rate can change at many different points along one fault in response to changing slip rates in other nearby faults.

“This study gives us the most accurate picture yet of how faults develop, which can be used to help assess seismic risk,” Elston says, and that’s just the beginning. The research in this paper, which was supported by the National Science Foundation, represents a proof of concept for the team’s analytical techniques. The future will detail 3D reconstructions of the evolution of the various defects.

Video overview of the team model is available on YouTube: https://www.youtube.com/watch?

Contacts: Hannah Elston, [email protected]

Daegan Miller, [email protected]

Article title

Unstable slip rates appear along sophisticated restrictive bends under continuous loading

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