Most earthquake energy doesn’t shake the ground - so where does it go?

We tend to think of earthquakes as a big, loud, ground-shaking event. The kind that rattles windows, knocks books off shelves, and sets off car alarms. But here’s something unexpected: all that shaking is just a fraction of the total energy an earthquake actually releases.

Most of the action takes place deep underground – and it’s mostly invisible. Scientists have known this for a while, but figuring out where all that energy really goes has been nearly impossible.

Now, researchers may have finally cracked the code – not in the field, but in the lab, with miniature quakes. And what they found is striking: earthquakes are mostly heat.

Shaking is just the beginning

In the lab, geologists created “lab quakes” by putting tiny chunks of rock under pressure until they snapped. These miniature quakes mimic the conditions deep underground, where real earthquakes happen.

And for the first time, scientists measured exactly how the energy from a quake gets divided. The results were surprising. Only about 10 percent of a lab quake’s energy caused shaking.

Less than one percent went into actually breaking rocks apart. A whopping 80 percent of the energy turned into heat – so much heat, in fact, that the rocks briefly melted.

Daniel Ortega-Arroyo, the study’s lead author, is a graduate student in MIT’s Department of Earth, Atmospheric and Planetary Sciences.

“In some instances we saw that, close to the fault, the sample went from room temperature to 1,200 degrees Celsius in a matter of microseconds, and then immediately cooled down once the motion stopped,” said Ortega-Arroyo. That kind of temperature spike is hotter than lava.

Studying earthquake behavior

The goal here wasn’t just to melt rocks for fun. These lab experiments are helping scientists understand how real earthquakes behave – especially the ones we can’t see coming.

Right now, most of what we know about earthquakes comes from seismometers, which measure the ground shaking at the surface. But that’s just one part of the story. Heat and underground rock fracturing are almost impossible to measure in the field, especially miles beneath our feet.

“We don’t know what’s happening to the rocks themselves, and the timescales over which earthquakes repeat within a fault zone are on the century-to-millenia timescales, making any sort of actionable forecast challenging,” Ortega-Arroyo said.

So instead of waiting around for another earthquake, the research team built a setup where they could study every part of one, under tightly controlled conditions.

Inside the mini-earthquake machine

To simulate a quake, the team ground up granite into powder and mixed it with special magnetic particles. These particles worked like internal thermometers – when the temperature changed, so did their magnetic signals.

The powdered rock, wrapped in a gold sleeve, was placed between pistons and squeezed until it slipped, just like rock layers do during a real earthquake.

The researchers used custom-made sensors to track shaking, and after each event, they examined the sample under a microscope to look for fractures.

“In one sample, we saw the fault move by about 100 microns, which implies slip velocities essentially about 10 meters per second. It moves very fast, though it doesn’t last very long,” Ortega-Arroyo said.

By combining all these measurements, the team calculated a full “energy budget” for each lab quake.

The memory of rocks

The researchers also found that a rock’s past matters. How much energy an earthquake puts into heat, shaking, or fracturing depends on whether the rock has already been bent, stretched, or cracked by earlier tectonic stress.

“The deformation history – essentially what the rock remembers – really influences how destructive an earthquake could be,” said Ortega-Arroyo. “That history affects a lot of the material properties in the rock, and it dictates to some degree how it is going to slip.”

That could help explain why some areas are more earthquake-prone than others, even if they sit along the same fault lines.

Improving predictive models

The researchers say their mini-quake machine doesn’t aim to copy nature exactly, but it gives them a way to isolate key processes – heat, shaking, and fracturing – and understand how they interact.

“We could never reproduce the complexity of the Earth, so we have to isolate the physics of what is happening, in these lab quakes,” said Professor Matěj Peč of MIT. “We hope to understand these processes and try to extrapolate them to nature.”

This knowledge could eventually improve how we model earthquakes and assess risk. For example, if a past earthquake created a lot of heat and broke apart rock underground, that could influence how future quakes play out in the same region.

“Our experiments offer an integrated approach that provides one of the most complete views of the physics of earthquake-like ruptures in rocks to date,” Peč said. “This will provide clues on how to improve our current earthquake models and natural hazard mitigation.”

Hidden energy of earthquakes

The next time the ground trembles, remember: the quake isn’t just rattling buildings. It’s heating rocks to over 2,000 degrees Fahrenheit, fracturing them at the microscopic level, and rewriting the energy map of the Earth’s crust.

We may not be able to stop earthquakes, but thanks to research like this, we’re getting closer to understanding how they really work – and how much energy they hide below the surface.

The full study was published in the journal AGU Advances.

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