Chile is no stranger to major earthquakes. The country experienced the strongest earthquake ever recorded in 1960, when a magnitude 9.5 megathrust event struck central Chile, triggering a massive tsunami and killing between 1,000 and 6,000 people. While devastating earthquakes are often linked to these massive megathrust events, the Calama earthquake stood apart from that familiar pattern.

Why This Earthquake Was Different

Megathrust earthquakes typically occur relatively close to the Earth’s surface, where tectonic plates collide. In contrast, the Calama earthquake originated far deeper underground. It ruptured at a depth of about 125 kilometers beneath the surface, inside the subducting tectonic plate itself.

Earthquakes that occur at these depths usually produce weaker shaking at the surface. However, the Calama event broke that expectation. Researchers at The University of Texas at Austin discovered that a rare sequence of underground processes significantly boosted the earthquake’s strength. Their findings were recently published in Nature Communications.

Beyond explaining why this earthquake was unusually intense, the study may also improve how scientists assess earthquake hazards in the future.

“These Chilean events are causing more shaking than is normally expected from intermediate-depth earthquakes, and can be quite destructive,” said the study’s lead author Zhe Jia, a research assistant professor at the UT Jackson School of Geosciences. “Our goal is to learn more about how these earthquakes occur, so our research could support emergency response and long-term planning.”

How Scientists Thought Deep Earthquakes Worked

Earthquakes at intermediate depths, including the Calama event, were long believed to be triggered mainly by a process known as “dehydration embrittlement.” This occurs as an oceanic tectonic plate sinks deeper into the Earth’s interior. As temperatures and pressures rise, water trapped in minerals is released.

When the rock loses this water, it becomes weaker and more brittle. Cracks can form, allowing the rock to suddenly rupture and generate an earthquake within the slab.

Scientists have generally believed that this dehydration process stops once temperatures exceed about 650 degrees Celsius.

A Rare Heat Driven Process Takes Over

The Calama earthquake challenged that assumption. According to the research team, the rupture continued well beyond the expected temperature limit. It traveled roughly 50 kilometers deeper into much hotter rock due to a second process known as “thermal runway.”

During this process, intense friction from the initial rupture generates extreme heat at the front of the fault. That heat weakens the surrounding material, allowing the rupture to keep moving forward and grow stronger as it spreads.

“It’s the first time we saw an intermediate-depth earthquake break assumptions, rupturing from a cold zone into a really hot one, and traveling at much faster speeds,” said Jia, who is part of the University of Texas Institute for Geophysics (UTIG), a research unit of the Jackson School. “That indicates the mechanism changed from dehydration embrittlement to thermal runaway.”

Tracking the Rupture Deep Underground

To understand how the earthquake unfolded and how far the rupture traveled, the University of Texas team worked with scientists in Chile and across the United States. They combined several lines of evidence to build a detailed picture of the event.

The researchers examined seismic records from Chile to track how fast and how far the rupture spread. They also used data from the Global Navigation Satellite System to measure ground movement and fault slip. Computer models helped estimate the temperatures and rock properties at the depths where the earthquake occurred.

Improving Earthquake Risk Forecasts

“The fact that another large earthquake is overdue in Chile has motivated earthquake research and the deployment of multiple seismometers and geodetic stations to monitor earthquakes and how the crust is deforming in the region,” said Thorsten Becker, a co-author of the study and a professor at the Jackson School’s Department of Earth and Planetary Sciences and a senior research scientist at UTIG.

Becker and Jia emphasized that understanding how earthquakes behave at different depths could improve predictions of future seismic events. Better models could help estimate how strong shaking might be, while also guiding infrastructure design, early warning systems, and rapid emergency response planning.

Research Support and Funding

The research was supported by the National Science Foundation, Agencia Nacional de Investigación y Desarrollo (ANID), Chile, UC Open Seed Fund, Fundamental Research Funds for the Central Universities, and the University of Texas Institute for Geophysics.

A new study published in the Proceedings of the National Academy of Sciences reports that being physically active increases the total amount of energy a person uses each day. The research, led by scientists at Virginia Tech working with colleagues from the University of Aberdeen and Shenzhen University, found that this increase happens without the body cutting back energy use in other areas.

The finding matters because while the health benefits of exercise are well established, scientists know less about how physical activity influences a person’s overall “energy budget,” which refers to how energy is divided among the body’s many functions.

How the Body Manages Energy

For years, researchers have debated whether the body treats energy like a fixed paycheck or a flexible bonus system. One idea suggests that when people move more, the body shifts energy away from other tasks to pay for that activity. The other model proposes that energy use can expand, allowing total daily expenditure to rise as activity increases. The researchers set out to learn which of these ideas best reflects what actually happens across different activity levels.

To answer that question, the team measured total energy expenditure, meaning the total number of calories burned in a day, among people with widely varying levels of physical activity.

“Our study found that more physical activity is associated with higher calorie burn, regardless of body composition, and that this increase is not balanced out by the body reducing energy spent elsewhere,” said Kevin Davy, professor in the Department of Human Nutrition, Foods, and Exercise and the principal investigator of the study.

Measuring Calories Burned in Real Life

Participants drank special forms of oxygen and hydrogen and provided urine samples over a two-week period. Oxygen leaves the body as both water and carbon dioxide, while hydrogen exits only as water. By comparing how much of each isotope was lost, researchers could estimate how much carbon dioxide participants produced and, in turn, how much energy they used. Physical activity was tracked using a small waist-worn sensor that recorded movement in multiple directions.

The study included 75 participants between the ages of 19 and 63. Activity levels ranged from largely inactive lifestyles to ultra-endurance running.

No Evidence the Body Cancels Out Exercise

The results showed that as people moved more, their total energy use increased accordingly. The body did not appear to compensate by dialing down energy use elsewhere. Essential functions such as breathing, blood circulation, and temperature regulation continued to require the same amount of energy, even as physical activity rose.

This means the body does not clearly offset or “cancel out” the extra calories burned through movement.

“Energy balance was a key piece of the study,” said Kristen Howard, senior research associate at Virginia Tech and the article’s lead author. “We looked at folks who were adequately fueled. It could be that apparent compensation under extreme conditions may reflect under-fueling.”

Less Sitting, More Moving

The researchers also observed a strong connection between higher activity levels and reduced time spent sitting. Simply put, people who move more tend to spend less time being inactive overall.

Taken together, the findings suggest that the long-debated idea that increased movement leads to increased calorie burn may be more accurate than some experts have assumed. While the results support the additive energy model, the researchers note that more work is needed. “We need more research to understand in who and under what conditions energy compensation might occur,” said Davy.