How did heat contribute to a rare earthquake in Chile?

Earthquakes deep within the Earth often follow strict physical boundaries. Heat, pressure, and softness of the rock usually prevent large cracks from spreading far. In July 2024, a powerful earthquake struck northern Chile challenged long-held ideas about deep earthquakes.

A hidden, heat-driven process allowed the rupture to travel deeper and faster than expected, releasing much more energy than standard models allow.

On July 19, 2024, a 7.4 magnitude earthquake struck near Calama in northern Chile. Shaking damaged buildings and power outages. Chile experiences frequent earthquakes, but most destructive events occur near the surface.

Kalama differed because the rupture began below the Earth's surface, within a submerged tectonic plate.

Chile has frequent strong earthquakes

Chile lies along the subduction zone where the Nazca plate slides beneath South America. Movement along plate boundaries creates frequent earthquakes. In 1960, central Chile experienced a 9.5 magnitude earthquake, the strongest ever recorded.

Most destructive Chilean earthquakes form near plate boundaries at shallow depths. Kalama occurred within the oceanic plate at a depth of about 125 kilometers (about 78 miles).

Earthquakes at such depths usually cause weaker shaking at ground level. Kalama broke this pattern.

Scientists from the University of Texas at Austin studied why such strong shaking occurred. The results appear in the journal Nature Communications and focus on the physics of tearing rather than surface damage alone.

Why do deep earthquakes occur?

Earthquakes between 70 and 300 kilometers (about 43 to 186 miles) deep fall into the moderate category.

At such depths, heat and pressure usually prevent sudden rock collapse. For decades, researchers have linked most mid-depth earthquakes to drought-induced embrittlement.

When a cold ocean plate sinks, minerals such as serpentine trap water within the crystalline structures. High temperature and pressure liberates the water from minerals. Water increases pressure within rocks, weakens mineral bonds, and allows sudden cracking.

Laboratory studies show that dehydration works at temperatures well below 650°C (about 1,200°F).

Above this temperature, rocks behave like soft solids and resist sudden fracture. For this reason, scientists believed that rupture should stop near those thermal limits.

Faster glide means more heat

Kalama challenged those limits. Seismic analysis revealed that the rupture moved about 50 kilometers (about 31 miles) deeper than expected, reaching areas hotter than 650 degrees Celsius (about 1,200 degrees Fahrenheit).

The researchers identified a second mechanism called thermal escape shear. During rupture, intense friction generates intense heat along the crack surfaces. The heat weakens the surrounding rock further, creating a feedback loop.

Faster sliding creates more heat, and more heat allows for faster sliding. The tear accelerates rather than stops.

“These Chilean events cause more tremors than would normally be expected from medium-depth earthquakes, and they can be very destructive,” said Zhi Jia, a research assistant professor at the UT Jackson School of Geosciences.

“It's the first time we've seen a medium-depth earthquake that breaks assumptions, exploding from a cold region into a very hot region, and moving at much faster speeds.”

“This indicates that the mechanism changed from drought-induced embrittlement to thermal escape.”

The rupture spread in a series of events

Seismic data showed that the rupture did not occur in one smooth motion. Instead, several sub-events were activated one after another.

Early rupture began near a depth of 125 kilometers (about 78 miles) within the core of a cooler slab. Subsequent rupture segments reached depths near 170 kilometers (about 106 miles), farther into hotter regions.

The early parts released only a small fraction of the total energy but produced many aftershocks. The later parts released the most energy and produced fewer aftershocks.

This behavior fits with thermal escape theory, as intense heating removes residual stress that could trigger aftershocks.

The rupture moved mainly downward along the steep fault plane rather than spreading laterally.

The average rupture speed was about 4.2 kilometers per second (about 2.6 miles per second), which is close to the speed of a shear wave. Such rapid motion remains rare for medium depth earthquakes.

How did the temperature form the earthquake?

The researchers used thermal models of the Chilean subduction zone to estimate the temperature at rupture depths.

Models have shown that cold slab cores remain relatively thin. The length of the rupture exceeded the thickness of the cold core, forcing it to spread into warmer regions.

Minerals other than serpentine, such as chlorite and talc, also release water, but these minerals are present in smaller quantities and at lower temperatures. Once the rupture enters the hotter areas, dehydration alone cannot explain continued failure.

Thermal escape provided a logical explanation for the continuous rupture at high temperature. The heat from friction weakened the rocks enough to allow sliding even in normally stable areas.

Why do risk estimates change?

“The fact that another major earthquake in Chile was delayed has stimulated seismic research and the deployment of multiple seismometers and geodetic stations to monitor earthquakes and how the crust is deforming in the region,” said Professor Thorsten W. Becker.

Kalama explains that deep earthquakes can activate areas that were considered too hot to rupture. Hazard models must take into account the combined effects of drought and thermal runaway.

Allowing rupture transitions increases the potential earthquake magnitude and shaking intensity.

Understanding hidden heat-driven processes improves earthquake prediction, infrastructure design and emergency planning.

Kalama offers a rare window into the depths of the Earth and highlights how extreme conditions can produce powerful earthquakes.

The study was published in the journal Nature Communications.

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