Second Seismic Anchor Point of the Martian Crustal Structure Away From the InSight Landing Site

Abstract

The most distant marsquake, S0976a, recorded so far by the InSight seismometer occurred at an epicentral distance of 146.3 ± 6.9o (Horleston et al., 2022), close to the western end of Valles Marineris. We have identified both SS and PP precursors, i.e., underside reflections off the crust-mantle (or intra-crustal) discontinuity between the marsquake and the instrument, on the seismograms, which directly constrain the crustal structure away (4000 km) from the InSight landing site. Inversion results show that the Martian crust at the bounce point between the lander and the event is characterized by an interface at 20 ± 5 km depth, similar to that seen beneath the InSight landing site (Knapmeyer-Endrun et al., 2021). However, a likely distinct feature at the bounce point compared to the lander site is the absence of a shallow layer (at 8 ± 2 km, with low seismic wave speed, Knapmeyer-Endrun et al., 2021), indicating that this layer is either local structure beneath the lander or related to the type of geologic unit or that has been obscured at the bounce point by later processes.

Different Martian Crustal Seismic Velocities Across the Dichotomy Boundary From Multi‐Orbiting Surface Waves

“…Since the ray paths of the above‐mentioned signals are nearly vertically incident beneath the seismometer, most of the sampled sub‐surface structures are limited to the vicinity of the InSight landing site (i.e., within a radius of ∼50 km). Nevertheless, there were attempts to constrain the crustal structures at other locations (e.g., Li, Beghein, McLennan, et al., 2022).…”