Seismic constraints on the crustal structure of Mars from InSight receiver functions

Abstract

NASA's InSight mission has for the first time placed a very broad-band seismometer on the surface of Mars. The Seismic Experiment for Inte-rior Structure (SEIS) has been collecting continuous data since early February 2019. The main focus of InSight is to enhance our understanding of the internal structure and dynamics of Mars, which includes the goal to better constrain the crustal thickness of the planet [1]. Knowing the present-day crustal thickness of Mars has important implications for its thermal evo-lution [2] as well as for the partitioning of silicates and heat-producing elements between the different layers of Mars. Current estimates for the crustal thickness of Mars are based on modeling the relationship between topography and gravity [3,4], but these studies rely on different assumptions, e.g. on the density of the crust and upper mantle, or the bulk silicate composition of the planet and the crust. The resulting values for the average crustal thickness differ by more than 100%, from 30 km to more than 100 km [5]. New constraints from InSight will be based on seismically determining the crustal thickness at the landing site. This single firm measurement of crustal thickness at one point on the planet will allow to con-strain both the average crustal thickness of Mars as well as thickness variations across the planet when combined with constraints from gravity and topogra-phy [6]. Here we describe the first constraints on the crustal structure and thickness at the InSight landing site based on seismic receiver functions for four marsquakes [7].