IRN Andes-FrenSZ webinar 8/10/2026

Webinars are organized on the first Thursday of each month at 2:30 pm UTC (4:30 pm in Paris, 9:30 am in Santiago, Chile).

Our webinars are a lively space to share research, exchange ideas, and build collaborations on subduction dynamics and related hazards (earthquakes, tsunamis, eruptions, landslides).

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October 10, 2026 | Flat Slabs

► Guido Gianni , Senior Researcher at the Institute of Geophysics of the Czech Academy of Sciences

How do flat slabs grow ? Insights from active and ancient flat subduction zones

Abstract : Flat-slab subduction is a distinctive feature of the active margins, with major consequences for magmatism, crustal deformation, seismicity, and the thermal structure of the overriding plate. While considerable attention has been devoted to understanding how flat slabs form, the mechanisms controlling their subsequent horizontal growth remain less clear. In this talk, I will examine the mechanisms responsible for flat-slab propagation by combining plate-kinematic reconstructions, observations from active and ancient flat-slab segments, and numerical modelling. Our results reveal two end-member modes of flat-slab propagation and indicate that forward propagation through underthrusting of the lower plate is the dominant mechanism in most cases. This behaviour shifts the focus from upper-plate advance, the prevailing view, toward the role of lower-plate kinematics and externally imposed convergence, potentially linked to slab pull from neighbouring subduction zones.