Seismic signals from Dust Devils on Mars
Résumé
We modeled the long-period seismic signals generated by Dust Devils and convective vortices on Mars. To characterize the source term, we used Large-Eddy Simulations with a spatial resolution of 50 m that resolve large turbulent and convective structures of the Martian atmosphere. The corresponding surface pressure fluctuations induce a quasi-static ground displacement and thus a tilt of the surface, which over weak soils can be detected by sensitive seismometers, as shown in terrestrial field experiments. Typical convective vortices on Mars have core-pressure drops of 2-5 Pa and generate tilt accelerations of 10-20 nm/s2 over a regolith halfspace, and of a few nm/s2 in the presence of a layer of harder rock at shallow depth. This signals are strong enough to be detected by the Very-Broad Band seismometer of the InSight/SEIS experiment up to a distance of several tens of meters from the vortex. The results of numerical simulations are compared to meteorological data from previous mission to Mars, and they give estimates of the encounter frequencies, showing how convective vortices will be routinely detected during the central hours of the day. A joint analysis of meteorological and seismic data will permit to distinguish atmospheric episodes from internal seimic sources and to investigate the structure and the elastic properties of the near surface at the InSight landing site.