Constraints on Lateral Variations of Martian Crustal Thickness From Seismological and Gravity Field Measurements

Using body wave arrival times from 31 seismic events recorded on Mars by the InSight mission, combined with topography and gravity field modeling, we constrained lateral variations of crustal thickness through a Bayesian inversion approach. The parameterization of the seismic structure relies on quantities that influence the thermochemical evolution of Mars, enabling the seismic velocities and densities in the different planetary envelopes to be consistently linked through common physical assumptions. Compared to a 1D structure, models with lateral variations of crustal thickness show two possible interpretations of the thermal evolution of Mars, with either a hot or cold scenario at the present-day. We found the hot scenario to be more compatible with InSight's radiotracking data and the tidal Love number. We relocated the marsquakes and derived maps of seismicity recorded by InSight, which is mostly located along or North of the boundary between the Northern lowlands and the Southern highlands. Thanks to the seismometer of the InSight mission, which recorded ground vibration measurements emanating from marsquakes and meteorite impacts during almost 4 years, the 1D interior structure of the crust, mantle, and core have been revealed. These models are mainly based on the assumption that the crustal thickness is similar everywhere on Mars. However, both the InSight lander and the most of the seismic events are located between the Northern lowlands and the Southern highlands where the crustal thickness varies widely, which can bias the interpretation of a 1D crustal model. In this study, combining the InSight seismic data with other independent geophysical measurements (topography and gravimetry data), we investigated to what extent the interior structure models are modified if lateral variations of crustal thickness are considered. Our results show that two different interpretations of Mars' thermal history can be considered, with either a hot or a cold scenario. We assessed the compatibility of our results with independent observations of oscillation of Mars' rotational axis, and found that the hot scenario is most likely. We infer lateral variation of Martian crustal thickness using InSight seismic data combined with topography and gravity field modeling Marsquakes are relocated and maps of the seismicity recorded by InSight are proposed Two families of models are found, leading to different interpretations of Mars' thermochemical evolution, with hot and cold scenarios