Crustal anisotropy as evidence for hydration of the Martian upper mantle

Abstract

Constraining the structure of the Martian lithosphere below the InSight lander is essential to our understanding of Elysium Planitia and the evolution of the whole planet. Previously, seismic imaging using data recorded by the SEIS instrument suggested three crustal interfaces at ∼8, ∼20, and ∼ 43 km depth. Additionally, a shallower small interface at ∼2 km has been identified. We estimate multiple-taper correlation receiver functions from records for 34 seismic events on Mars. We extend the bandwidth of frequencies considered and offer the finest vertical resolution yet. We conduct shear-wave splitting analysis and stochastic inversion of P-to-s converted phases to estimate anisotropic parameters of the major crustal layers. Our analysis identifies anisotropy (12–14 %) in the lower layers of the Martian crust. We suggest that the deepest layer of the Martian crust beneath InSight formed during modification of the upper mantle during volcanism, not differentiation generated by Borealis impactor. Our proposed underplating process could have been metasomatic and involved hydration from an early ocean on Mars.