Whether studying microscopic fractures in the laboratory or earthquakes in the Earth’s crust, Jesse Hampton is interested in the same question: how are individual cracking events connected?
Hampton, a recently tenured associate professor of civil and environmental engineering at the University of Wisconsin-Madison, says the cracks, or fractures, in rocks are “fractal.” That means they tend to follow similar, branching patterns at different scales—whether that’s along a sprawling, miles-long fault line or a tiny crack in a rock you can hold in your hand.
“It’s kind of like a snowflake,” Hampton says. “If you zoom into a very small scale on the snowflake, you’ll see a pattern. Zoom out and you’ll see that pattern at a bigger scale. For seismicity, if you look at the lab scale, we have microcracks, which behave similarly to natural and induced earthquakes; helping us learn a lot from lab-scale experiments.”
While it’s common to use those similarities to study earthquake behavior or to focus on an individual earthquake catalog consisting of datasets that include thousands of earthquakes, Hampton’s research steps further by studying the connections among earthquakes. For example, one earthquake might trigger another shortly after and in the immediate vicinity. But sometimes, Hampton says, an earthquake can influence seismic activity surprisingly far away, revealing long-range stress communication through the Earth’s crust.
With funding from a U.S. Department of Energy Early Career Award, Hampton is studying how tiny seismic events connect to one another and organize into larger patterns under different stress conditions. Those lab-scale events, called nanoseismicity, can mirror larger seismic systems because rock fractures behave similarly across scales. Hampton is using machine learning to identify and locate vast numbers of tiny seismic events in laboratory experiments. He then uses graph theory to determine how those events are connected and how stress propagates through rock.
Mapping these connections can reveal tree-like structures, with roots, branches and leaves that represent how seismic activity propagates through rock. Hampton says even the shapes of the trees—dense and branching like a conifer or long and sparse like a palm—can reveal information about earthquake relationships.
“The cool thing about this is that we’re only measuring what’s happening with individual earthquakes,” Hampton says. “But with all of that data, we can say something about a fundamentally different scale. We’re connecting the dots between earthquakes and reconstructing how damage and stress move through rock. That gives us a way to see processes that were previously hidden.”
Hampton’s research could deepen understanding of how fractures spread below the earth’s surface. That could be critical for industries like geothermal energy, which circulates fluids through hot rock deep underground to extract heat, which can trigger weak earthquakes known as induced seismicity.
“Understanding these connections helps us get better at harvesting geothermal energy,” Hampton says. “It helps us better understand how fractures develop and interact within geothermal reservoirs, which can ultimately improve energy production while reducing the risk of larger induced seismicity events.”
The DOE’s Office of Basic Energy Sciences is supporting Hampton’s research with an $880,000 grant. The project will run for five years. The DOE Early Career Award is among the agency’s most competitive awards for young faculty members and supports researchers who are expected to become leaders in their fields.
Featured image caption: Civil and environmental engineering PhD student Ana Paula Villaquirán Vargas checks equipment in a geological engineering lab. Vargas works with Associate Professor Jesse Hampton to measure how stress propagates through rocks. Photo: Joel Hallberg.