Abstract
We report observations of Rayleigh waves that orbit around Mars up to
three times following the S1222a marsquake. Averaging these signals, we
find the largest amplitude signals at 30 s and 85 s central period,
propagating with distinctly different group velocities of 2.9 km/s and
3.8 km/s, respectively. The group velocities constraining the average
crustal thickness beneath the great circle path rule out the majority of
previous crustal models of Mars that have a >200 kg/m3
density contrast across the dichotomy. We find that the thickness of the
martian crust is 42-56 km on average, and thus thicker than the crusts
of the Earth and Moon. Together with thermal evolution models, a thick
martian crust suggests that the crust must contain 50-70% of the total
heat production to explain present-day local melt zones in the interior
of Mars.