Mountain Chain Beneath the Sea : How Buried Seamounts Shape Earthquakes and Slow Slip in Chile

Figure 7 : Schematic of structural and petrological controls on fault behavior (not to scale). Subducted seamounts, rich in altered volcaniclastic material forming clays, promote velocity-strengthening, aseismic slip (Hacker et al., 2003 ; Volpe et al., 2024). Mechanical loading of the Copiapo Ridge enhances slab hydration and fluid release via mineral dehydration, altering fault properties. Hydrated zones without seamounts and drier seamount zones together enable fluid mobilization and clay supply, influencing slip behavior and earthquake arrest. The P-T diagram (Behr & Bürgmann, 2021 ; Ji et al., 2019) outlines metamorphic transitions related to slab dehydration, highlighting the need for thermal-mechanical models to better define fluid release depths.

Recent research reveals that undersea mountains (seamounts) dragged deep beneath the Earth’s surface along tectonic plate boundaries significantly influence how faults slip and produce earthquakes.

This study focuses on the Copiapo Ridge subduction zone off the coast of northern Chile, where two buried seamounts ; referred to as A1 (shallow) and A2 (deeper), shape fault behavior by interacting with fluids trapped within the Earth’s crust and mantle. These fluids reduce the normal stress on faults, making them more prone to silently slow, processes known as aseismic slip or slow slip events (SSEs), rather than sudden seismic ruptures as earthquakes. Meanwhile, the mechanical effects of seamounts locally increase stress, causing a complex slip mode involving seismic and aseismic slip.

At shallow depths near seamount A1, clay-rich rocks strengthen the fault and promote slow slip, while deeper zones around seamount A2 show enhanced fluid movement and damage, creating ideal conditions for long-lasting SSEs.

This combination of geological structures and fluids creates a patchy, dynamic environment along the fault, controlling where and how the fault slips, sometimes smoothly, sometimes suddenly.

This findings suggest that subducted topography and fluid circulation together govern earthquake and slow slip patterns, not only in Chile but likely in many other subduction zones worldwide.

The full study is published in JGR Solid Earth

References :

Münchmeyer, J., Molina-Ormazabal, D., Radiguet, M., Marsan, D., Baez, J.-C., Ortega-Culaciati, F., et al. (2025). Seismic swarms unveil the mechanisms driving shallow slow slip dynamics in the Copiapó ridge, Northern Chile. Geophysical Research Letters, 52, e2024GL113953.

Saffer, D. M., & Marone, C. (2003). Comparison of smectite-and illite-rich gouge frictional properties : Application to the updip limit of the seismogenic zone along subduction megathrusts. Earth and Planetary Science Letters, 215(1–2), 219–235.

Saffer, D. M., & Tobin, H. J. (2011). Hydrogeology and mechanics of subduction zone forearcs : Fluid flow and pore pressure. Annual Review of Earth and Planetary Sciences, 39(1), 157–186.

Todd, E. K., Schwartz, S. Y., Mochizuki, K., Wallace, L. M., Sheehan, A. F., Webb, S. C., et al. (2018). Earthquakes and tremor linked to seamount subduction during shallow slow slip at the Hikurangi margin, New Zealand. Journal of Geophysical Research : Solid Earth, 123(8), 6769–6783.

Volpe, G., Collettini, C., Taddeucci, J., Marone, C., & Pozzi, G. (2024). Frictional instabilities in clay illuminate the origin of slow earthquakes. Science Advances, 10(26), eadn0869.

Gase, A. C., Bangs, N. L., Saffer, D. M., Han, S., Miller, P. K., Bell, R. E., et al. (2023). Subducting volcaniclastic-rich upper crust supplies fluids for shallow megathrust and slow slip. Science Advances, 9(33), eadh0150.

Dascher-Cousineau, K., & Bürgmann, R. (2024). Global subduction slow slip events and associated earthquakes. Science Advances, 10(35), eado2191.

Wallace, L., Kaneko, Y., Hreinsdóttir, S., Hamling, I., Peng, Z., Bartlow, N., et al. (2017). Large-scale dynamic triggering of shallow slow slip enhanced by overlying sedimentary wedge. Nature Geoscience, 10, 765–770.

Scientific Contacts :

• Anne Socquet Researcher, ISTerre – Université Grenoble Alpes, France
• Diego Molina-Ormazabal Researcher, CNES, France
• Mathilde Radiguet Researcher, ISTerre – Université Grenoble Alpes, France
• Jannes Münchmeyer Researcher, DECODE Project, European Union
• Nicolas Hernandez-Soto Researcher, ISTerre – Université Grenoble Alpes, France
• Adrien Vezinet Researcher, ISTerre – Université Grenoble Alpes, France
• Lea Pousse-Beltran Researcher, ISTerre – Université Grenoble Alpes, France
• Catalina Castro Researcher, Universidad de Chile, Chile
• Marie-Pierre Doin Researcher, ISTerre – Université Grenoble Alpes, France
• Juan Carlos Baez Researcher, ANID, Chile
• Marcos Moreno Researcher, ANID, Chile
• Andres Tassara Researcher, Universidad de Chile, Chile
• Philippe Durand Researcher, ISTerre – Université Grenoble Alpes, France

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Mountain Chain Beneath the Sea : How Buried Seamounts Shape Earthquakes and Slow Slip in Chile

Recent research reveals that undersea mountains (seamounts) dragged deep beneath the Earth’s surface along tectonic plate boundaries significantly influence how faults slip and produce earthquakes.

References :

Scientific Contacts :