Structure Along the Martian Dichotomy Constrained by Rayleigh and Love Waves and their Overtones
Using seismic recordings of event S1222a, we measure dispersion curves of Rayleigh and Love waves, including their first overtones, and invert these for shear velocity (Vs) and radial anisotropic structure of the martian crust. The crustal structure along the topographic dichotomy is characterized by a fairly uniform vertically-polarized shear velocity (Vsv) of 3.17 km/s between ~5-30 km depth, compatible with the previous study by Kim et al. (2022). Radial anisotropy as large as 12 % (Vsh > Vsv) is required in the crust between 5-40 km depth. At greater depths, we observe a large discontinuity near 63 ± 10 km, below which Vsv reaches 4.1 km/s. We interpret this velocity increase as the crust-mantle boundary along the path. Combined gravimetric modeling suggests that the observed average crustal thickness favors the absence of large-scale density differences across the topographic dichotomy.