In July 2024, the city of Calama in Northern Chile experienced a powerful 7.4-magnitude earthquake that caused widespread damage to infrastructure and significant power outages. While Chile is notoriously vulnerable to seismic events due to its position along the seismically active Chilean subduction zone, the nature of this particular earthquake deviated dramatically from the common pattern of the region’s most devastating quakes. Unlike the shallow megathrust earthquakes that have historically shaped the country’s seismic profile, the Calama event originated much deeper beneath the Earth’s surface, challenging existing paradigms about the mechanics of intermediate-depth seismicity.
Chile’s seismic history is marked by the catastrophic 1960 Valdivia earthquake, which remains the most powerful earthquake ever recorded, with a magnitude of 9.5. This megathrust event generated a massive tsunami and resulted in thousands of fatalities. Generally, megathrust earthquakes occur at relatively shallow depths along the interface where the Nazca tectonic plate subducts beneath the South American plate, releasing enormous amounts of energy that translate into violent surface shaking. However, the Calama earthquake ruptured at an unusual depth of approximately 125 kilometers, well within the descending tectonic slab itself, classifying it as an intermediate-depth event rather than a classical megathrust.
Such deep-focus earthquakes typically produce less intense shaking at the surface due to the attenuation of seismic waves over distance. Yet, the Calama earthquake defied these expectations by generating strongly felt shaking and causing damage disproportionate to what is normally observed for its depth. A groundbreaking study from a collaborative research team led by the University of Texas at Austin reveals a series of previously unknown geophysical mechanisms that likely contributed to the extraordinary intensity of the Calama event. This research, published in the journal Nature Communications, provides a new framework for understanding how intermediate-depth earthquakes in Chile—and potentially elsewhere—can be more destructive than anticipated.
The conventional explanation for intermediate-depth earthquakes for many years has been tied to a process known as “dehydration embrittlement.” As oceanic plates descend into the hotter mantle beneath continental plates, increasing pressure and temperature cause water bound within hydrous minerals to be expelled. This release of fluid weakens the rock structure, promoting brittle failure along faults in the subducted slab, and thereby triggering earthquakes. Notably, this process is typically limited to conditions below approximately 650 degrees Celsius, where mineral dehydration reactions cease. The Calama quake, however, penetrated well beyond this thermal threshold, indicating an additional, more complex mechanism at play.
Researchers discovered that the initial rupture likely began in a cold, brittle zone where dehydration embrittlement was active, but then propagated 50 kilometers deeper and into zones exceeding 650 degrees Celsius. This unprecedented rupture depth was attributed to a phenomenon termed “thermal runaway.” During thermal runaway, intense frictional heating generated at the tip of the fault slip causes a feedback loop: heat weakens the surrounding rocks further, making it easier for the rupture to accelerate and extend into hotter zones. The rupture speed observed in the Calama earthquake also exceeded typical rates for intermediate-depth events, highlighting a significant transition in the earthquake’s physical rupture processes.
According to Zhe Jia, lead author and research assistant professor at the University of Texas Jackson School of Geosciences, the Calama earthquake represents a novel type of earthquake rupture that breaks longstanding assumptions in seismology. The transition from dehydration embrittlement to thermal runaway explains how this earthquake was able to maintain high energy release despite its occurrence at such depths. These findings challenge existing models that predict reduced seismic hazard from intermediate-depth earthquakes and underscore the need to reconsider earthquake hazard assessments.
To dissect the detailed seismic mechanics of the Calama earthquake, the research team integrated a variety of geophysical datasets and analytical techniques. High-resolution seismic data from Chile allowed them to map the rupture propagation and evaluate the rupture speed in unprecedented detail. Global Navigation Satellite System (GNSS) data provided precise measurements of fault slip and crustal deformation. Additionally, sophisticated computer simulations were employed to estimate subsurface temperatures and the changing composition of the subducted slab where the rupture occurred. This multidisciplinary approach was crucial in revealing the geodynamic complexity behind the event.
The insights gained from the Calama earthquake study have wide-reaching implications for earthquake science, especially in subduction zone environments similar to Chile’s. Professor Thorsten Becker, co-author and UTIG senior research scientist, emphasized that an overdue large earthquake in the region has driven significant advancements in monitoring technology and deployment of seismic and geodetic stations. Continuous monitoring is essential to improve understanding of how stress accumulates and is released at different slab depths, potentially providing valuable precursors for future seismic hazards.
Moreover, the study highlights the importance of integrating advanced physical models into earthquake hazard mitigation efforts. By recognizing that intermediate-depth earthquakes can involve a transition to thermal runaway mechanisms, hazard forecasts can be refined to better anticipate the intensity of shaking and its destructive potential. This can enhance the sophistication of infrastructure design codes, early-warning algorithms, and emergency response plans in Chile and other subduction zone countries with similar geological settings.
The Calama event also raises intriguing questions about the physical conditions within subducted slabs that allow such rupture transitions. Understanding mineral phase transformations, fluid dynamics, and frictional heating effects deep within the Earth’s interior opens new frontiers in the study of earthquake nucleation and propagation. Reverberations from this research can extend to global seismic hazard assessments, as many other convergent plate boundaries experience intermediate-depth seismicity whose mechanisms remain incompletely understood.
Funding for this investigation was provided by a constellation of agencies and foundations, including the United States National Science Foundation, Chile’s Agencia Nacional de Investigación y Desarrollo (ANID), the UC Open Seed Fund, and the University of Texas Institute for Geophysics. This research exemplifies the vital role of international collaboration and cross-disciplinary approaches in addressing complex geoscientific challenges related to natural disasters.
In sum, the 2024 Mw 7.4 Calama earthquake has not only highlighted an unusual and potentially hazardous mode of seismic rupture but also expanded the scientific community’s understanding of deep-earthquake mechanics. By elucidating the transition from dehydration embrittlement to thermal runaway, this study heralds a paradigm shift in seismology and earthquake hazard preparedness, with the potential to save lives and protect infrastructure in some of the world’s most tectonically active regions.
Subject of Research: Earthquake mechanics; deep intra-slab earthquake rupture; thermal runaway processes in seismology
Article Title: Deep intra-slab rupture and mechanism transition of the 2024 Mw 7.4 Calama earthquake
News Publication Date: 30-Aug-2025
Web References: https://www.nature.com/articles/s41467-025-63480-5
References: DOI 10.1038/s41467-025-63480-5
Image Credits: Thorsten Becker/UT Austin
Keywords: Seismology, Geophysics, Earthquakes, Natural disasters
