In July 2024, a magnitude 7.4 earthquake occurred near Calama in northern Chile, causing building damage and electrical power disruptions. This event was notable for originating at an approximate depth of 125 kilometers within a subducting tectonic plate, yet producing stronger surface shaking than typically observed for intermediate-depth earthquakes. New research, led by The University of Texas at Austin, has identified a sequence of underground processes, including a mechanism shift from dehydration embrittlement to thermal runaway, that contributed to the earthquake's strength and deeper rupture.
The Calama Earthquake Event
The magnitude 7.4 earthquake near Calama in northern Chile in July 2024 resulted in localized building damage and electrical power outages. The event occurred at an approximate depth of 125 kilometers, deep within the subducting tectonic plate. Earthquakes at such depths usually lead to less intense surface shaking, however, the Calama earthquake generated surface intensity that exceeded typical expectations for intermediate-depth events. Chile has a history of significant seismic activity, including the 1960 magnitude 9.5 megathrust earthquake.
Research Findings on Rupture Mechanism
Researchers at The University of Texas at Austin, in collaboration with scientists in Chile and the United States, investigated the factors contributing to the Calama earthquake's characteristics. Their findings, published in Nature Communications, propose an explanation for the event's amplified strength.
Historically, intermediate-depth earthquakes have been primarily attributed to "dehydration embrittlement." This process involves the release of water from minerals within an oceanic tectonic plate as it descends and is subjected to increasing temperatures and pressures. This release of water is understood to weaken the rock, leading to rupture and seismic activity. This process was believed to largely cease when temperatures reached approximately 650 degrees Celsius.
The Calama earthquake rupture, however, extended approximately 50 kilometers deeper into hotter rock, beyond the previously understood 650-degree Celsius temperature limit for dehydration embrittlement. This deeper propagation is attributed to a secondary process identified as "thermal runaway." During thermal runaway, intense friction generated by the initial rupture produces extreme heat at the fault front. This heat then weakens the surrounding material, allowing the rupture to continue and intensify.
Zhe Jia, a research assistant professor at the UT Jackson School of Geosciences and the study's lead author, stated that this event indicated a mechanism shift from dehydration embrittlement to thermal runaway.
Methodology and Broader Implications
The research team utilized multiple data sources to analyze the earthquake's progression. These sources included seismic records from Chile, which were used to track rupture speed and extent, and Global Navigation Satellite System (GNSS) data, which measured ground movement and fault slip. Computer models were also employed to estimate temperatures and rock properties at the earthquake's depth.
Thorsten Becker, a co-author and professor at the Jackson School, highlighted that understanding earthquake behavior at different depths can enhance predictions of future seismic events. Improved models could assist in estimating shaking intensity, informing infrastructure design, early warning systems, and emergency response planning.
The research received support from 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.