Surface waves and crustal structure on Mars

Abstract

We detected surface waves from two meteorite impacts on Mars. By measuring group velocity dispersion along the impact-lander path, we obtained a direct constraint on crustal structure away from the InSight lander. The crust north of the equatorial dichotomy had a shear wave velocity of approximately 3.2 kilometers per second in the 5- to 30-kilometer depth range, with little depth variation. This implies a higher crustal density than inferred beneath the lander, suggesting either compositional differences or reduced porosity in the volcanic areas traversed by the surface waves. The lower velocities and the crustal layering observed beneath the landing site down to a 10-kilometer depth are not a global feature. Structural variations revealed by surface waves hold implications for models of the formation and thickness of the martian crust.

Crustal Anisotropy in the Martian Lowlands From Surface Waves

“…Most remarkably, S1222a generated surface waves clearly observable on all three components of the ground motion (Figure 2). While Rayleigh waves have been previously detected on Mars with impact events S1000a and S1094b (Kim et al, 2022), no Love waves had been seen before. Since Rayleigh and Love waves are predominantly sensitive to different elastic parameters (governing the speed of vertically and horizontally polarized shear waves traveling horizontally, respectively), this gives us an opportunity to study the presence of large-scale radial seismic anisotropy on Mars between the lander and the event epicenter.…”

Observation of a Core‐Diffracted P‐Wave From a Farside Impact With Implications for the Lower‐Mantle Structure of Mars

“…Since its deployment, the SEIS (Seismic Experiment for Interior Structure) instrument (Lognonné et al., 2019) as part of the InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) lander has been passively recording marsquakes (Banerdt et al., 2020) for over 1300 Sols (a Sol is a Martian day and corresponds to ∼24 hr 40 min) since landing, including ∼90 marsquakes at teleseismic distances with moment magnitudes ( M w ) in the range 2.5–4.2 (Ceylan et al., 2022; Clinton et al., 2021; InSight Marsquake Service, 2022). The analysis of marsquakes has resulted in a significant improvement in our understanding of Martian seismicity (Giardini et al., 2020) and interior structure (Lognonné et al., 2020), including crustal and lithospheric thickness, crustal and mantle velocity structure, and core size and mean density (Drilleau et al., 2022; Durán et al., 2022; Khan et al., 2021, 2022; Kim, Lekić, et al., 2021; Kim et al., 2022; Knapmeyer‐Endrun et al., 2021; Stähler et al., 2021). Yet, because of the absence of P‐waves that have traversed the lower mantle (below ∼800 km depth), the deep mantle P‐wave velocity structure remains unconstrained.…”

Constraints on the martian crust away from the InSight landing site

“…Constraining the crustal structure at other locations is, however, crucial to fully understand the formation and evolution of the crust, and to improve global models of crustal thickness based on gravity data 17 . Although surface waves have been recently detected for the first time from two meteorite impacts 18 , 19 and the largest marsquake ever recorded 20 , surface waves constrain the average structures along the event-lander path 19 , 21 , 22 and are less sensitive to subsurface discontinuities. The present work aims at providing seismic constraints on the crustal structure at a location far from the InSight lander.…”