Modeling of atmospheric Rayleigh waves generated by airbursts on Earth and Mars

Meteor impacts are important for Planetary Seismology, as they are a primary source of seismic waves on planets with limited tectonic activity. When a meteor reaches the surface of a planet, both body and surface seismic waves are generated. If it explodes into the atmosphere, due to ablation, shock waves are generated and propagated down to the solid surface. Due to the atmospheric/ground coupling, this mainly leads to the excitation of Rayleigh waves in the solid part. Understanding this excitation is important for the preparation of planetary seismic experiments on Mars, such as SEIS (Seismic Experiment of Interior Structure) of the imminent Martian mission InSight. In this study, this excitation is modeled on Earth and Mars, using two different approaches. In the first approach, we compute synthetic seismograms using summation of the normal modes of the full planet (i.e. solid with atmosphere). We use these seismograms to invert seismic data of the Global Seismographic Network recorded during the Chelyabinsk bolide event and obtain a seismic moment representation of it. The inversion involves several source points along the trajectory of the bolide. The duration of the seismic source is typically associated to the radiation duration of shock waves until they reach the linear regime of propagation. We then apply the method to the case of Mars. The second approach is a coupled approach: the atmospheric burst is modeled with a sonic boom calculation software, PCBOOM, that computes the map of the acceleration produced by the airburst on the ground. This footprint is then used as input by SPECFEM3D, a Spectral-Element method code, to model the propagation of Rayleigh waves in a 3D model of the planet. A comparative study between Mars and Earth is performed, using equivalent sources that are similarly modeled in different atmospheric, impact size and lithospheric conditions and are comparatively analyzed, for providing constraints on the seismic source duration.