Siersch, Nicki ; Xu, Fang ; Greaux, Steeve ; Badro, James ; Kuwahara, Hideharu ; Kondo, Nozomi ; Kono, Yoshino ; Higo, Yuji ; Plesa, Ana-Catalina ; Rivoldini, Attilio ; Antonangeli, Daniele

Poster presented at AGU Fall Meeting 2020, Virtual on 2020-12-16

Abstract: InSight, equipped with the seismometer SEIS, landed on Mars in November 2018 and since early 2019 records the global seismic activity with the final goal to acquire geophysical data to infer Mars’ internal structure. The knowledge of density and elastic properties of relevant minerals and mineralogical assemblages at pertinent thermodynamic conditions is crucial in order to fully exploit the seismic records from SEIS and to produce accurate models of Mars in terms of composition, structure and dynamics. In this study, we measured sound wave velocities and densities of selected Martian mantle lithologies by combined ultrasonic, X-ray radiography and X-ray diffraction experiments carried out in the 1500-tons multi-anvil apparatus at BL04B1, SPring-8. Two samples were pre-crystallized at 3 and 8 GPa from a glass of Martian mantle bulk composition. The pressure used in the experiments correspond to the pressure of Mars’ upper and mid mantle, respectively. Compressional velocity vP, shear velocity vS, and density have been measured as a function of pressure and temperature, covering the P-T conditions of the olivine stability field inside the mantle of Mars. Our results show that the dependence of vP/vS on the lithology and temperature is weak at shallow mantle conditions. Furthermore, through fitting of the P-T dependencies of each assemblage it was possible to calculate vP and vS along mantle temperature profiles obtained from 3D thermal evolution studies assuming either a thin (45 km) or thick (87 km) crust. For the temperature profiles resulting from the thin crust models, we find that low velocity zones are present for vP and vS whereas thick crust models exhibit only a low velocity zone for vS. These findings provide therefore important guidance for the interpretation of seismic observations. Moreover, our experiments will help to characterize potential vS shadow zones inside Mars’ mantle that have been suggested to explain some of the seismic events recorded by InSight.

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Funding: 3PRODPLANINT/3PRODPLANINT/3PRODPLANINT