[S19-4] Science goals and modeling of the Insight/SEIS experiment

[S19-4-04] Modeling the seismic signals generated by dust devils on Mars

^○Balthasar Kenda^{1, 2}, Philippe Lognonne¹, Aymeric Spiga³, Taichi Kawamura⁴, Sharon Kedar², Bruce Banerdt², Ralph Lorenz⁵, Don Banfield⁶, Matt Golombek² (1.Institut de Physique du Globe de Paris, Paris, France, 2.Jet Propulsion Laboratory, California Institute of Technology, Pasadena, USA, 3.Universite Pierre et Marie Curie, Paris, France, 4.National Astronomical Observatory of Japan, Japan, 5.Johns Hopkins University Applied Physics Laboratory, Laurel, USA, 6.Cornell University, Ithaca, USA)

The 2018 InSight mission to Mars will deploy the Seismic Experiment for Interior Structure (SEIS) at the surface of the red planet. In addition to the signals generated by quakes and meteor impacts, the SEIS seismometers will continuously measure the excitation produced by the atmosphere. Among the signals of meteorological origin, dust devils and convective vortices are of special interest since they are localized, frequent and ubiquitous on Mars and they have a characteristic seismic signature.
We modeled the long-period (T > 10 s) signals of dust devils based on Large-Eddy Simulations of the daytime atmospheric dynamics at the InSight landing site and on the quasi-static response of the ground to pressure loading. Results show that vortices with typical pressure drops of 1-3 Pa can generate tilt effects of 5-20 nm/s^2 over the weak regolith. These are well above the detection threshold, and the influence area extends to a few hundreds of meters away from the vortex core. The catalog of episodes in the simulation is used to estimate the detection rate at a single station, which is expected to be as high as one episode per Martian day. Different subsurface models were considered and the possibility of using pressure and seismic data to determine the compliance of the Martian regolith is discussed. In an analog terrestrial field study, dust devils also produced infrasounds and higher-frequency seismic waves interpreted as shallow surface waves propagating in the subsurface. These additional signals contribute to better locate the vortex and to estimate the seismic velocities of the Martian subsurface down to a few tens of meter depth.