Seismology on Mars: An analysis of direct, reflected and converted seismic body waves with implications for interior structure

With the arrival of InSight on Mars and the deployment of SEIS on the surface, Mars represents the second extra-terrestrial body for which we have seismic data (Banerdt et al., 2020). The successful detection of marsquakes and their analysis allow us to obtain better constraints on the interior structure of Mars, in particular, crust, mantle and core (Knapmeyer-Endrun et al., 2021; Khan et al., 2021; Stahler et al., 2021). To date, more than 1000 events have been detected, but the majority of these events comprise small amplitude marsquakes that are difficult to resolve above the background ambient noise. In this study, we focus on 14 high-quality events recorded to date by InSight (InSight Marsquake Service, 2021) and provide a complete reanalysis using polarisation filtering, time-domain envelopes, followed by polarisation analysis of the direct (P and S), reflected (PP, SS, and ScS), and converted (P-to-s and S-to-p) body wave arrivals. With these phase picks and differential travel times (relative to P) constructed therefrom, we perform a preliminary inversion for distance and interior structure, while predicting the arrival times of other seismic phases (e.g., PPP, SSS and PcS) that are subsequently compared with the seismic data. This allows us to enlarge our initial set of phase picks, after which we perform another joint location-interior structure inversion to update the initial results. The procedure works iteratively and seeks to continuously update location and model structure with information from the latest seismic events. Our new interior structure models generally agree with those published earlier (Knapmeyer-Endrun et al., 2021; Khan et al., 2021; Stahler et al., 2021), but also show some new features that will prove important for furthering our understanding of the interior structure of Mars. References: Banerdt, W. B., et al. 2020, Nat. Geo., 13, 183, doi: 10.1038/s41561-020-0544-y InSight Marsquake Service. 2021, Mars Seismic Catalogue, InSight Mission; V6 2021-04-01, ETHZ, IPGP, JPL, ICL, MPS, Univ. Bristol, doi: 10.12686/a11 Khan, A., et al. 2021, Science, 373, 434, doi: 10.1126/science.abf2966 Knapmeyer-Endrun, et al. 2021, Science, 373, 438, doi: 10.1126/science.abf8966 Stahler, S. C., et al. 2021, Science, 373, 443, doi: 10.1126/science.abi7730