How fault lines in a kitchen sink change what we know about geology

In a new article recently published in the journal Geology, Researchers at the University of Massachusetts Amherst have unveiled a physical model that provides unprecedented, high-resolution insight into fault slip rates, which determine the likelihood of earthquakes.

When most of us imagine a fault line, we imagine a giant crack in the earth where two tectonic plates collide. When geologists think of faults, however, they see a branching system made up of thousands of individual faults. “The closer you look,” says Michele Cooke, one of the paper’s co-authors and professor of geosciences at UMass Amherst, “the more you find, and when you look in detail, the picture becomes very complicated”.

Such complexity makes it difficult to accurately understand what is happening at any given location in the system, let alone predict when and where an earthquake will occur. To further blur the picture, the vast majority of individual faults are buried under soil or obscured by vegetation, and therefore cannot be observed directly. Finally, fault systems evolve over thousands, tens of thousands, or even millions of years. Therefore, geologists have traditionally generated generalized slip rates for entire fault systems and come up with general theories about the evolution of fault systems.

In a new study, the authors used a physical model, “about the size of a kitchen sink,” says Hanna Elston, the paper’s lead author and a graduate geoscience student at UMass Amherst, and plotted it. filled with a carefully compounded kaolin clay, “about the consistency of Greek yogurt”, which behaves much like the earth’s crust. At the bottom of the model are two plates that can be moved with precision. Elston and his co-authors then carefully cut the clay, to form a fault, and, over the course of four hours, which simulated a million years, moved the plates 12 centimeters, while taking pictures with a array of aerial cameras, which they could then analyze to discover the slip rates and mechanics of their modeled faults.

The precision of the one-of-a-kind technique developed by Elston and his co-authors allows them to track slip rates at specific locations along faults, with unprecedented fidelity, which can then provide a record that researchers can directly compare to the field. studies to estimate the slip rate at a particular point along a fault.

Not only does the model work in a way that mirrors real-life flaws, it allowed Elston and his colleagues, including Cooke and Alex Hatem, now at the US Geological Survey, to observe two different phenomena that no one else has ever seen. have seen before. First, the model shows that slip rates can change at a particular site on the fault as that fault evolves. Second, the team showed that slip rates are interactive: the rate can change at many different points along a fault in response to changing slip rates on other nearby faults.

“This study gives us the finest picture to date of faulting evolution, which could be used to help with seismic hazard assessment,” says Elston – and this is just the beginning. The research in this paper, which was supported by the National Science Foundation, represents proof of concept for the team’s analytical techniques. The future will detail the 3D reconstructions of the evolution of the various faults.

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Material provided by University of Massachusetts at Amherst. Note: Content may be edited for style and length.

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