In a groundbreaking study published in Nature Communications, researchers have unveiled critical insights into the 2024 Mw 7.4 Calama earthquake, an event that has sent seismic waves of concern through the geoscience community. This major earthquake, occurring deep within the slab of the subducting Nazca plate, has revealed a complex rupture mechanism that defies conventional understanding. The investigation highlights a dramatic transition in the earthquake’s rupture mechanism as it propagated, illuminating deep processes within Earth’s interior that challenge previous models of seismic behavior in subduction zones.
The Calama earthquake struck the north-central region of Chile, a highly active seismic area due to the convergence of the Nazca and South American plates. Unlike more typical shallow interplate earthquakes that release stress on the plate interface, this event originated deep within the subducting slab itself – an intra-slab rupture occurring at an extraordinary depth and over a significant distance. This depth component makes the earthquake particularly interesting for scientists seeking to understand the mechanical behavior of slabs under extreme pressure and temperature conditions.
Detailed seismic waveform analysis and geophysical imaging have revealed that the rupture did not propagate uniformly. Instead, the earthquake exhibited a clear mechanism transition. Initially, the rupture began along a strike-slip faulting regime, characterized by horizontal displacement, but as it propagated, the faulting mechanism transitioned abruptly to a thrust-faulting regime, where vertical motion dominated. This transition is indicative of complex stress interactions within the descending slab, suggesting that the forces at play evolve considerably with depth and along the slab’s geometry.
The research team employed state-of-the-art deep seismic tomography and back-projection techniques to unravel this intricate rupture process. These methods enabled them to resolve not only the overall geometry of faulting but also the temporal evolution of slip during the event. The findings reveal that the rupture propagated over 60 kilometers within the slab, with the initial strike-slip component occupying approximately the first half, after which thrust faulting became predominant. This kind of rupture behavior challenges traditional classifications and requires a reassessment of seismic hazard models in subduction zones globally.
One of the remarkable aspects of the Calama earthquake’s rupture is its association with significant deeper mantle processes, far from the interface usually responsible for megathrust quakes. This intra-slab rupture occurred at depths of roughly 70–100 kilometers, a realm where slab bending, thermal gradients, and mineral phase transitions influence mechanical properties profoundly. The earthquake thus offers a rare natural laboratory to investigate how these deep Earth processes control brittle failure, stepping beyond conventional shallow seismicity.
The authors argue that this mechanism transition during rupture could reflect a stress reorganization triggered by changes in lithological composition or temperature within the slab. Mineral transformations or slab dehydration reactions occurring at depth might alter frictional properties or generate elevated pore fluid pressures, facilitating shifts in fault mechanics. This hypothesis is supported by correlations between seismic velocity anomalies and regions of high fluid release identified in their tomographic models.
This revelation holds profound implications for seismic risk assessment. While deep intra-slab earthquakes produce less destructive surface shaking compared to shallow interplate events, their unexpected rupture complexity and energy release patterns can influence ground motions unpredictably, affecting infrastructure and population centers differently than previously assumed. Moreover, deep slab events are less well integrated into early warning systems due to their unusual signatures and challenging detectability.
Significantly, the study emphasizes that the transition in faulting mechanism is not merely a theoretical curiosity but alters how stress and strain distribute throughout the slab and its interfaces. This insight reshapes our understanding of how subducted plates deform and conclude their eventual fate at mantle depths, influencing long-term geodynamic processes including slab rollback, mantle flow, and plate boundary evolution. These deep seismic events may thus serve as indicators of mantle-slab interactions previously inaccessible to direct observation.
The calibrated seismic dataset from the Calama earthquake also contributes to refining global earthquake source models. The nuanced temporal evolution of rupture, changing from strike-slip to thrust motion, challenges assumptions embedded into moment tensor inversions commonly used to characterize earthquakes. Enhancing these models with real-world examples of mechanism transition aids in producing more accurate earthquake source imaging, vital for both scientific knowledge and practical hazard mitigation.
Supporting the comprehensive analysis, the multidisciplinary team incorporated geological and geodetic datasets along with seismic data. Strain accumulation patterns and historic seismicity records in the broader region corroborate the unusual nature of this deep rupture event. The data collectively advocate for a reevaluation of seismic coupling and strain release in the southern segment of the Nazca plate, implying that energy storage and release mechanisms within subducting slabs are more diverse and dynamic than previously comprehended.
Looking forward, the authors suggest that similar deep intra-slab rupture mechanisms might be more common in other subduction zones but remain under-recognized due to limitations in seismic monitoring sensitivity at depth. Expansion of dense seismic arrays and advances in computational seismic processing will be critical to detecting and characterizing these complex rupture behaviors. Moreover, integrating petrological and mineral physics studies could clarify the physical conditions fostering mechanism transitions.
The Calama earthquake thus stands as a vivid illustration of Earth’s inner workings, revealing that the seemingly solid, cold slabs descending into the mantle are tectonically alive, undergoing dynamic rupture processes that differ markedly from surface-level quakes. These findings will invigorate further research into deep Earth seismology and encourage revisiting interpretations of historical intra-slab events worldwide.
In essence, this study unlocks a new frontier in earthquake science. It bridges seismology, mineral physics, and geodynamics by demonstrating how rupture propagation can evolve within the Earth’s depths, orchestrating an unexpected symphony of faulting mechanisms. As our planet’s subduction zones continue to generate earthquakes with complex behavior, such transformative investigations deepen our grasp on seismic hazard and the fundamental processes shaping our restless planet.
By illuminating the throbbing interior of the Nazca slab beneath Chile, the 2024 Calama earthquake study unravels a vital chapter of subduction zone physics. The revelation of a deep intra-slab rupture with a distinct mechanism transition marks a milestone in seismological research. This event is set to influence not only how scientists understand earthquake mechanics but also how policymakers approach seismic risk in tectonically active regions worldwide.
The study’s technical sophistication and its broad implications highlight the importance of multidisciplinary approaches in earthquake science. By incorporating high-resolution imaging, advanced rupture modeling, and geological context, the research represents an exemplary integration of modern Earth science techniques.
Ultimately, the 2024 Calama earthquake serves as a powerful reminder that the planet’s interior is an arena of dynamic processes, where even deep, hidden faults can unleash seismic energy in unexpected and profound ways. The knowledge gained from this event heralds a new era of seismic understanding, spurring innovations in monitoring, modeling, and risk preparedness in earthquake-prone regions around the globe.
Subject of Research: Deep intra-slab earthquake rupture and mechanism transition within the subducting Nazca plate during the 2024 Mw 7.4 Calama earthquake.
Article Title: Deep intra-slab rupture and mechanism transition of the 2024 Mw 7.4 Calama earthquake.
Article References:
Jia, Z., Mao, W., Flores, M.C. et al. Deep intra-slab rupture and mechanism transition of the 2024 Mw 7.4 Calama earthquake. Nat Commun 16, 8140 (2025). https://doi.org/10.1038/s41467-025-63480-5
Image Credits: AI Generated
