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The Martian subsurface structure at the InSight landing site revealed by marsquakes

We analyzed the seismological data collected by the InSight mission, which landed on Mars in November 2018, in order to reveal the first tens of meters of the subsurface structure underneath the landing site. Here, we performed horizontal-to-vertical analysis (H/V) for different wind-dependent noise periods and for martian seismic events data (marsquakes). The final H/V curve presents a characteristic trough at 2.4 Hz and a strong peak at 8 Hz. We inverted this H/V curve for the 1D shear-wave velocity structure at the InSight landing site. Based on our inversion results, we propose a strong site effect at the InSight site to be due to the presence of a shallow high-velocity layer (SHVL) over low-velocity units. The SHVL is likely placed below a layer of coarse blocky ejecta and can be associated with Early Amazonian basaltic lava flows. The units below the SHVL have lower velocities, possibly related to a Late Hesperian or Early Amazonian epoch with a different magmatic regime and/or a greater impact rate and more extensive weathering. An extremely weak buried low-velocity layer (bLVL) between these lava flows explains the data around the 2.4 Hz trough, whereas a more competent bLVL would not generate this latter feature. These subsurface models are in good agreement with results from hammering experiments and compliance measurements at the InSight landing site. Finally, this site effect is revealed only by seismic events data and it explains the larger horizontal than vertical ground motion recorded for some marsquakes.


Sebastian Carrasco1, Brigitte Knapmeyer-Endrun1, Ludovic Margerin2, Cédric Schmelzbach3, Keisuke Onodera4, Lu Pan5, Philippe Lognonné6, Sabrina Menina6, Domenico Giardini3, Eléonore Stutzmann7, John Clinton8, Simon Stähler3, Martin Schimmel9, Matthew Golombek10, Manuel Hobiger11, Miroslav Hallo8, Sharon Kedar10, W. Bruce Banerdt10
1University of Cologne, Germany; 2Institut de Recherche en Astrophysique et Planétologie, Université Toulouse III Paul Sabatier, Toulouse, France; 3Institute of Geophysics, ETH Zurich, Zurich, Switzerland; 4Institut de Physique du Globe de Paris, CNRS, Université de Paris, Paris, France;The Graduate University for Advanced Studies (SOKENDAI), Kanagawa, Japan; 5Center for Star and Planet Formation, University of Copenhagen, Copenhagen, Denmark; 6Institut de Physique du Globe de Paris, CNRS, Université de Paris, Paris, France; 7The Graduate University for Advanced Studies (SOKENDAI), Kanagawa, Japan; 8Swiss Seismological Service (SED), ETH Zurich, Zurich, Switzerland; 9Geosciences Barcelona - CSIC, Barcelona, Spain; 10Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA; 11Swiss Seismological Service (SED), ETH Zurich, Zurich, Switzerland;Federal Institute for Geosciences and Natural Resources (BGR), Hannover, Germany
GeoMinKöln 2022