Mars Subsurface Structure Investigation from InSight using a Monte-Carlo Method

Seismic scattering provides critical insights into the internal structure and dynamics of planetary interiors. In this study, we analyze marsquakes waveform data collected during the InSight mission to investigate the effects of mantle heterogeneities on P-wave propagation. We apply a monte-carlo, particle-based phonon model [1] to derive the seismic scattering on Mars following the approach used to constrain the Earth’s mantle heterogeneities. With this model, we infer 1-D scattering parameters of the shallow subsurface of Mars from existing values of layer depths, mean seismic velocities and mean density by extracting the power spectra of crustal heterogeneity. The model’s envelopes provide good fits to the seismic-energy profiles of both direct arrivals and coda seen InSight’s nearby impacts (S1034a, S0793a, S0981c, S0986c). Our best-fitting parameters reflect existing interior models [2] to more accurately capture the complex scattering behavior in multi-layer heterogeneous media. We apply this model to frequencies up to and beyond 10 Hz, a regime which is better suited to monte-carlo, particle-based modelling compared to other techniques such as finite-difference and spectral-element computation. This model can be extended to distinguish more distant impacts from shallow marsquakes and constrain the scattering contribution of subsurface water [3].

[1] Shearer, P. M., & Earle, P. S. (2004). The global short-period wavefield modelled with a Monte Carlo seismic phonon method. Geophysical Journal International, 158(3), 1103-1117.

[2] Drilleau, M., Beucler, É., Shi, J., Knapmeyer‐Endrun, B., Garcia, R. F., Ansan, V., ... & Banerdt, W. B. (2023). Structure of the Martian crust below InSight from surface waves and body waves generated by nearby meteoroid impacts. Geophysical Research Letters, 50(23), e2023GL104601.

[3] Sun, W., Tkalčić, H., Malusà, M. G., & Pan, Y. (2025). Seismic evidence of liquid water at the base of Mars' upper crust. National Science Review, nwaf166.