A massive earthquake struck Calama, Chile, in July 2024, surprising scientists with its extraordinary strength despite occurring deep underground. Measuring 7.4 in magnitude, the quake damaged buildings, caused power outages, and challenged long-standing assumptions about intermediate-depth earthquakes.

Unlike shallow megathrust quakes, which typically generate the strongest shaking, the Calama quake occurred 125 kilometers beneath the Earth’s surface, within the subducting tectonic slab. Deep earthquakes usually produce milder surface effects, but this event unleashed unexpectedly intense shaking due to a rare “thermal runaway” mechanism.

Researchers at The University of Texas at Austin, in a study published in Nature Communications, found that the earthquake’s rupture breached traditional thermal limits. Normally, intermediate-depth quakes are triggered by dehydration embrittlement—a process where water is expelled from minerals under heat and pressure, weakening the rock. This mechanism typically stops around 650°C.

However, the Calama quake penetrated hotter zones 50 kilometers deeper. Friction from the initial rupture generated additional heat, weakening surrounding rock and propelling the rupture forward at high speed. “It’s the first time we saw an intermediate-depth earthquake transition from dehydration embrittlement to thermal runaway,” said lead author Zhe Jia, a research assistant professor at UT’s Jackson School of Geosciences.

To understand the quake’s behavior, the UT team collaborated with researchers in Chile and the U.S., combining seismic data, Global Navigation Satellite System measurements, and computer simulations to map the rupture’s speed, deformation, and temperature conditions.

“This event shows that earthquakes at intermediate depths can be far more destructive than previously thought,” said co-author Thorsten Becker, professor at UTIG. Understanding these mechanisms may help predict shaking intensity for future events, guide infrastructure planning, and improve early warning systems.

Chile, which experienced the largest recorded earthquake in history—a 9.5-magnitude megathrust in 1960—has long been a focus for seismic monitoring. The Calama quake’s unusual depth and thermal behavior highlight the need for enhanced earthquake preparedness and research.

Funding for this research came from the National Science Foundation, Chile’s Agencia Nacional de Investigación y Desarrollo (ANID), UC Open Seed Fund, Fundamental Research Funds for Central Universities, and the University of Texas Institute for Geophysics.