Structure of the Martian Crust Below InSight From Surface Waves and Body Waves Generated by Nearby Meteoroid Impacts

We measure group velocity dispersion of surface waves generated by two meteoroid impacts on Mars close to the lander of the InSight mission. This allows us to probe the crustal structure in the first few kilometers beneath the InSight lander. In combination with body wave arrival times from five impact events, we obtain direct seismic constraints on the seismic velocity of the crust in the vicinity of the InSight landing site. We confirm the existence of a uppermost low-velocity layer with a mean thickness of similar to 1.2 km, interpreted as layered volcanic materials, possibly interstratified with sedimentary and altered materials. Our joint inversion of surface and body waves shows a four-layer model for the Martian crust, compatible with high- and low-frequency P-to-S receiver functions estimated in previous studies. The knowledge of the crustal structure of Mars is essential for understanding the formation and evolution of the planet. Thanks to the Very Broadband Seismometer of the InSight mission which landed on the surface of Mars (its operational life lasted almost four terrestrial years), seismic signals generated by meteoroid impacts have been recorded. Five craters have been identified by orbital imaging to be located within a circle of similar to 250 km radius around the lander. For two of these meteoroid impacts, we measured surface waves for the first time, which are mostly sensitive to the crustal structure in the first kilometers below the InSight lander. Our surface wave analysis, in combination with other measurements, are compatible with a crustal model in the vicinity of the InSight lander made of four layers, with a shallow low velocity layer similar to 1.2 km thick. We verified the compatibility of our results with independent observations from previous studies. Group velocity dispersion generated by two meteoroid impacts (S0986c and S1034a) near the InSight landing site is measuredA shallow low-velocity crustal layer of similar to 1.2 km thickness explains both surface wave and body wave observationsA four-layer crustal model is obtained, compatible with surface waves, body waves, and receiver function measurements