.
Venus is often called Earth’s sister planet due to its similar size and mass. Apart from that, however, the two planets are wildly different, with surface temperatures on Venus that easily melt lead and a Venusian surface pressure that is almost a hundred times larger than that of Earth. Additionally, Venus is completely covered in clouds; obscuring its surface and shrouding the entire planet in mystery.
How did the observed topographic features form? Is there still some form of tectonics ongoing? Are there earthquakes - or indeed: venusquakes?
These are just a few of the questions that Venus scientists would love to know the answer to. Luckily, several planetary missions will explore Venus in the coming decade. Focusing on tectonics, volcanism, and Venus’ atmosphere, missions like EnVision, VERITAS, and DAVINCI will likely provide rich new datasets to start answering the multitude of questions we have about Venus’ current and past state.
Until then, modelling is a useful tool to gain a first-order understanding of the physical processes on Venus. In addition, models can be used to make predictions and end-member hypotheses that can be directly tested by the upcoming missions.
To gain first insights on how the observed rifting structures on the Venusian surface could have formed, we adapted 2-D thermomechanical numerical models of continental rifting on Earth to Venus-like environments. Our results show that a strong crustal rheology such as dry diabase is needed to localise strain and develop rifts under the high surface temperature and pressure of Venus. Models with different crustal thicknesses fit the topography profiles of the Ganis and Devana Chasmata well, indicating that the differences in these rift features on Venus might be due to different crustal thicknesses.
The rifts of Venus are potentially still seismically active and so could the fold belts and a subset of the coronae be. Scaling the seismicity of the Earth to Venus by identifying potential analogues for different tectonic settings, allowed us to provide several end-member estimates of the potential seismicity on Venus. Our most realistic estimate for a moderately active Venus results in a prediction of a few thousand venusquakes with magnitude 4 or higher per Earth year.
To assess the feasibility of measuring this seismicity with future missions, we estimated the seismic wave detectability of different ground-based, atmospheric, and orbital techniques. Airglow imagers, which can measure seismic wave patterns in the airglow of the upper atmosphere from orbit, appear to be the most promising technique due to their long mission duration, although they are limited to detecting larger magnitude events.
In summary, since we are faced with many unknowns when it comes to Venus, this interdisciplinary approach that combines modelling aspects from both geodynamics and seismology and integrates observational techniques is the way forward to exploring the tectonics and seismicity of Venus and unravel the mysteries of this planet.
How to cite: van Zelst, I., Garcia, R. F., Regorda, A., Maia, J., De Toffoli, B., Plesa, A.-C., Thieulot, C., Erdős, Z., and Buiter, S. and the ISSI team #566 - Seismicity on Venus: Prediction & Detection: Exploring the tectonics and seismicity of Venus , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6949, https://doi.org/10.5194/egusphere-egu25-6949, 2025.
During the past 15 years I and my colleagues have studied the dynamics of free (gravity-driven) subduction using a twofold approach: numerical simulations using the boundary-element method (BEM), and interpretation of the solutions using the theory of thin viscous shells. The basic model comprises a shell with thickness h and viscosity η1 subducting in a mantle with viscosity η2. The mantle has a finite depth H (in 3-D Cartesian geometry) or an outer radius R0 (in spherical geometry). The key length scale governing subduction is the 'bending length' lb, the sum of the slab length and the lateral extent of the seaward flexural bulge. A dimensionless 'flexural stiffness' St = (η1/η2)(h/lb)3 determines whether the subduction rate is controlled by η1 or η2. 3-D BEM simulations closely reproduce laboratory experiments, and reveal the physical mechanisms underlying the different modes of subduction observed. In spherical geometry, subduction is controlled by St and a 'dynamical sphericity number' Σ = (lb/R0) cotθt, where θt is the angular radius of the trench. Spherical BEM solutions demonstrate the 'sphericity paradox' that the effect of sphericity on flexure is greater for small (more nearly flat) plates than for large ones (e.g. hemispherical). Another surprising result is that state of stress in a doubly-curved slab is dominated by the longitudinal normal ('hoop') stress. BEM predictions of hoop stresses in slabs with positive and negative Gaussian curvature agree well with earthquake focal mechanisms in the Mariana slab. Linear stability analysis shows that a slab under compressive hoop stress is unstable to longitudinal buckling, which may explain the peculiar geomery of the Mariana slab. Finally, I will describe a new hybrid boundary-integral/thin-shell approach to coupling mantle flow with the deformation of a thin shell having non-Newtonian rheology.
How to cite: Ribe, N.: Thin-shell dynamics of subduction, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1740, https://doi.org/10.5194/egusphere-egu25-1740, 2025.
