Martian Crustal Model From a Joint Inversion of Receiver Functions and Apparent Shear Wave Velocity

Abstract

AbstractReceiver function (RF) based studies have revealed the layered Martian crustal structure beneath the InSight, which provides key information about the composition, rock alteration, deep magma process, and thermal history of Mars. However, limited by the frequency and trade‐offs between the thickness and velocity, inverting RFs alone is difficult to provide an accurate image of the upper crust. Here, by achieving stable measurements of the apparent shear wave velocities (Vs,app) at different frequencies for high‐quality marsquakes, we perform a joint inversion with the RFs. Our crustal models differ from previous models by having an extra shallow structure in the upper crust, either a layer with a sharp velocity jump interface at 4.0 ± 0.9 km depth or a gradient structure with shear wave velocity increasing gradually from 1.1 ± 0.1 km/s near the surface to 1.7 ± 0.3 km/s at a depth of 6.0 ± 2.4 km, which well fits both RFs and Vs,app's. Such an upper crustal velocity model is consistent with the depth‐decaying of porosity due to self‐compaction and indicates a highly porous upper crust with a surface porosity larger than 30%. Besides, a much higher porosity decay constant than that scaled from the Moon is derived, suggesting different mechanical properties of the lunar and Martian crust.