(Bordeaux, salle 2 de l’IMB)

  • 14h00-15h00 Anne Mangeney (Institut de Physique du Globe de Paris): Recovering ice mass loss in Greenland from seismic data and mechanical modelling.
  • 15h00-16h00 Lisl Weynans et David Lannes (IMB): Generating boundary conditions and floating objects in Boussinesq systems.

Anne Mangeney (Institut de Physique du Globe de Paris) Recovering ice mass loss in Greenland from seismic data and mechanical modelling (joint work with Amandine Sergeant, Pauline Bonnet, Vladislav Yastrebov, Olivier Castelnau, Eléonore Stutzmann, Jean-Paul Montagner, and Patrick Quetey). Quantification of ice mass loss is a key issue to better understand the impact of climate change and in particular to constrain regional and global circulation models. The Greenland ice sheet is losing mass as a result of both increased surface melting and runoff and increased ice discharge from marine-terminating outlet glaciers. Ice discharge at these glaciers includes submarine ice melting and iceberg production. Calving of icebergs generate glacial earthquakes of magnitudes up to 5 that can be recorded at 100’s of km from the source. These waves result from the forces applied by km-scale icebergs against the terminus face, as they slowly capsize. Long-period inversion of the recorded seismic signal makes it possible to calculate these forces. Former studies failed to recover iceberg volume from the earthquake magnitude or from the maximum force due to the complex physical processes involved. We recently showed that numerical modelling of the iceberg capsize taking into account the interplay between these processes help constraining seismic inversion, making it possible to recover icebergs volume. This coupled seismic and modelling approach allows to monitor ice-mass loss from iceberg capsize in Greenland over a 20-year period of recorded glacial seismicity and to investigate its relation to climate change, ocean temperature, or glacier dynamics.

Lisl Weynans et David Lannes: Generating boundary conditions and floating objects in Boussinesq systems. Boussinesq systems are dispersive perturbations of the (hyperbolic) nonlinear shallow water equations, and are widely used for applications in coastal oceanography and more recently for the description of wave-structure interactions (eg for marine renewable energies). We shall consider two different phenomenons in this talk, in which we exhibit a dispersive boundary layer that plays an important role:
– Generating boundary conditions: for numerical simulations, one quantity (eg the surface elevation) is known at the entrance of the domain, and one is let to solve an initial boundary value problem. The theory is known for hyperbolic systems but there is no general theory in the presence of dispersion. Several techniques have been proposed, which are often difficult to implement and/or time consuming. We present here a simple method based on the analysis of the dispersive boundary layer, and that can be implemented without extra computational cost.
– Nonlinear dispersive waves with a floating object (joint work with D. Bresch and G. Métivier). We consider here a the interaction of wave described by a Boussinesq system with a floating object. We show that the problem can be reduced to a simple transmission problem (and even to an ODE) and show how to solve it by analysing the dispersive boundary layer.