Lithology, Pore-Filling Media, and Pore Closure Depth Beneath InSight on Mars Inferred From Shear Wave Velocities

摘要

We quantify the volume and distribution of water, cement, sediments, and fractured rocks within the Martian crust beneath NASA's InSight (Interior Exploration using Seismic Investigations, Geodesy, and Heat Transport mission) lander by using rock physics models to interpret shear wave velocities (Vs) measured from InSight data. The models assume that Mars' crust comprises sediments and fractured rocks whose pores and fractures host variable combinations of gas, liquid water, and mineral cements. Measured Vs in the upper crust (0-8 km) can be explained by layers of minimally (<2%) cemented sediments and gas-filled fractured basalts. Measured Vs in the deeper crust (8-20 km) can be explained by fractured basalts or more felsic igneous rocks (modeled here as 100% plagioclase feldspar) that is unfractured or has up to 23% porosity. Open pores in the deeper crust could host gas, liquid water, and up to 2% cement. Modeled Vs are too low for a seismically detectable ice-saturated cryosphere in the upper crust and temperatures are too high to freeze liquid water in the deeper crust. Notably, with Vs alone, we are unable to distinguish between liquid water and gas within the pores.