Including GD Division Outstanding ECS Award Lecture
Earth's mantle drives fundamental processes that shape our planet and directly impact us. Convective flow induces both lateral and vertical motion of the surface, with consequences across timescales. Over geological time, dynamic topography modulates continental flooding, sedimentary basin development, and global sea level. On shorter timescales, glacial isostatic adjustment governs the ongoing response to ice sheet fluctuations, reshaping coastlines and redistributing ocean mass. These vertical motions, coupled with lateral plate displacements, also control the burial and exhumation of rocks, processes central to the genesis of mineral and critical resource deposits. Quantitative models of mantle dynamics are therefore essential not only for understanding Earth's past but for anticipating its future trajectory.
Traditional forward modelling approaches, while physically rigorous, fail to fully exploit the wealth of observational constraints now available, including seismic tomography, geodetic measurements, tectonic reconstructions, and geological indicators of past topography. These data encode invaluable information about mantle structure and rheology that forward models cannot systematically assimilate.
Here I present a framework for constructing Digital Twins of Earth's Mantle, physics-based models systematically optimised against observations using formal inverse methods. Central to this approach is the adjoint method, which enables efficient computation of gradients through complex time-dependent simulations, making large-scale inversions tractable.
I demonstrate this framework across three complementary problems spanning temporal scales. For long-term mantle evolution, I show how seismic tomography and plate reconstructions can be inverted to recover Earth's mantle history in the Cenozoic. Turning to the present day, I illustrate how observations of dynamic topography constrain three-dimensional variations in mantle rheology. Finally, addressing shorter timescales, I consider glacial isostatic adjustment, where the joint reconstruction of ice loading history and mantle viscosity structure emerges from geodetic and geological sea-level data.
Together, these applications establish adjoint-based Digital Twins as powerful tools for synthesis across Earth science disciplines, enabling both retrodiction of past states and predictions that inform sea level projections, coastal vulnerability assessment, and mineral exploration.
How to cite: Ghelichkhan, S.: Digital Twins of Earth's Mantle: Adjoint Inverse Approaches for Reconstructing Mantle Dynamics, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19971, https://doi.org/10.5194/egusphere-egu26-19971, 2026.
Subduction zones play a key role in the tectonic and chemical evolution of the Earth and are the site of the largest earthquakes and most explosive volcanic eruptions. Subduction zones are diverse, varying in rates, shape of the trench and slab, relative contribution and direction of trench motion versus plate motion, coupling between the two plates, and state of stress of the upper plate.
To understand what controls such diversity, my group and several others have been building a systematic understanding of subduction dynamics, starting from the simplest system of a single subducting plate, free subduction. Free subduction models illustrate how sensitive the subduction system is to the balance between slab density which drives it, the resistance of the plate to bending at the trench (and base of the transition zone) and drag by the mantle below the unsubducted plate and around the slab. Tectonic reconstructions and seismic tomography show that in response to the extra resistance to sinking encountered at the transition to the lower mantle most slabs retreat and flatten. Such observations constrain the magnitude of slab strength relative to the other forces. Any dynamic models of subduction, even for investigating more complex dynamic settings, need to ensure plate properties yield such an earth-like sinking mode of subduction.
Varying trench shapes can be understood from variations in plate width, which lead to simple C-shaped trenches for small subduction zones or W-shapes for trenches that are long relative to slab bending lengths. Although slab pull is the dominant driver of mantle convection, local (plate-age) dependent slab buoyancy does not have a strong expression in trends of plate and trench velocities, indicating the importance of considering spatially varying plate buoyancy. Models show that buoyant features such as aseismic volcanic ridges can lead to either slab steepening or flattening depending on the background plate buoyancy and strength and position relative to the free-subduction shape of the trench. Together, these factors explain quite a bit of the complexity seen in natural subduction zones. Further influences come from global plate interactions, which limit the motions of upper and lower plates, and mantle flow including upwellings and flow driven by previously subducted slab remnants.
The resulting imbalance between the bending a free slab tries to achieve and the bending it undergoes to adjust to the net forces acting on the system affects how much of the deformation is viscous versus elastic. An initial study showed that a measure of this elasticity (the Deborah number) may correlate with the proportion of larger relative to smaller intraplate earthquakes. In my talk, I will present a summary of some of these key previous insights into subduction dynamics and natural examples.
How to cite: Goes, S.: Towards understanding the dynamics of subduction zone diversity, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10356, https://doi.org/10.5194/egusphere-egu26-10356, 2026.
Speakers
- Siavash Ghelichkhan, Australian National University, Australia
- Saskia Goes, Imperial College London, United Kingdom