Journal Article

Global Crustal Thickness Revealed by Surface Waves Orbiting Mars

Lekić, V., McLennan, S. M., Ceylan, S., Davis, P., Khan, A., Giardini, D., Knapmeyer‐Endrun, B., Duran, C., Lognonné, P., Banerdt, W. B., Plesa, A.‐C., Boehm, C., Wieczorek, M., Stähler, S. C., Clinton, J. F., Panning, M. P., Kim, D.

2023

Overview

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 and 85 s central period, propagating with distinctly different group velocities of 2.9 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 equatorial dichotomy between northern lowlands and southern highlands. 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. Considered with the context of 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. Plain Language Summary The NASA InSight mission and its seismometer installed on the surface of Mars is retired after ∼4 years of operation. From the largest marsquake recording during the entire mission, we observe clear seismic signals from surface waves called Rayleigh waves that orbit around Mars up to three times. By measuring the wavespeeds with which these surface waves travel at different frequencies, we obtain the first seismic evidence that constrains the average crustal and uppermost mantle structures beneath the traveling path on a planetary scale. Using the new seismic observations together with gravity data, we confirm that the density of the crust in the northern lowlands and the southern highlands is similar, differing by no more than 200 kg/m3. Furthermore, we find that the global average crustal thickness on Mars is 42–56 km, much thicker than the Earth's and Moon's crusts. By exploring Mars' thermal history, a thick Martian crust requires about 50%–70% of the heat‐producing elements such as thorium, uranium, and potassium to be concentrated in the crust in order to explain local regions in the Martian mantle that can still undergo melting at present day. Key Points We present the first observation of Rayleigh waves that orbit around Mars up to three times Group velocity measurements and 3‐D simulations constrain the average crustal and uppermost mantle velocities along the great‐circle propagation path The global average crustal thickness is 42–56 km and requires a large enrichment of heat‐producing elements to explain local melt zones

• Publisher: John Wiley & Sons, Inc,American Geophysical Union,Wiley
• Subject: Concretions / crust / Crustal thickness / Crusts / Density / dichotomy / Earth / Earth mantle / Earth-Moon system / Enthalpy / Gravity data / Great circles / Highlands / Lowlands / Mars / Mars surface / marsquake / Moon / Planetary mantles / Potassium / Rayleigh waves / Sciences of the Universe / Seismic activity / Seismic waves / Seismometers / Surface waves / Thermal evolution / Thickness / Thorium / upper mantle / Uranium