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Deep Lithospheric Rupture and Dual-mechanism Transition During the 2024 Mw 7.4 Calama Earthquake, Chile

Description: 

The mechanism of intermediate depth earthquakes (70-300 km depth) remains enigmatic, with leading hypotheses attributing rock failure to either dehydration embrittlement or thermal runaway instabilities. Here, we estimate the rupture details of the 2024 Calama Mw 7.4 intermediate-depth earthquake using a dense local network of seismometers, accelerometers and cGNSS stations deployed in tNorthern Chile, and teleseismic seismograms, and compare the rupture extent with the temperature environment resolved from thermo-mechanical simulations. Time series reveal several short-duration pulses of P and S waves, along with coseismic displacements that extended over 300 km from the epicenter and exceeded 10 mm. These observations indicate a maximum slip of approximately 1 meter, concentrated within a vertical rupture plane characterized by five distinct subevents inside the slab. Rupture of the vertical plane is consistent with the location of aftershocks. The subevent and slip models suggest that the rupture nucleated within the cold core of the subducting slab, likely driven by dehydration embrittlement mechanism, before propagating deeper and engaging multiple asperities. Remarkably, the rupture extended into warmer regions, well beyond the serpentine dehydration isotherms, suggesting that a transition to shear thermal instability likely facilitated the later stages of rupture propagation. This is the first time an intermediate-depth earthquake in Chile has been characterized in such detail, including regional deformation and high resolution seismicity. The dual-mechanism transition extends the potential rupture zones beyond recognized seismogenic boundaries, which emphasizes the need to consider the complex interactions between rupture mechanisms and slab thermal and compositional structures for understanding large intermediate-depth earthquakes.

Session: Unusual Earthquakes and Their Implications [Poster]

Type: Poster

Date: 4/16/2025

Presentation Time: 08:00 AM (local time)

Presenting Author: Zhe

Student Presenter: No

Invited Presentation: 

Poster Number: 16

Authors