Variable Daily Autocorrelation Functions of High-Frequency Seismic Data on Mars

High-frequency seismic data on Mars are dominated bywind-generated lander vibrations, which are radiated partially to the subsurface. Autocorrelation functions (ACFs) of seismic data on Mars filtered between 1 and 5 Hz show clear phases at similar to 1.3, similar to 2.6, and similar to 3.9 s. Daily temporal changes of their arrival times (dt/t) correlatewellwith the daily changes of ground temperature, with similar to 5% daily variation and similar to 50 min apparent phase delay. The following two mechanisms could explain the observations: (1) the interference of two predominant spectral peaks at similar to 3.3 and similar to 4.1 Hz, assumed to be both lander resonance modes, generate the apparent arrivals in the ACFs; (2) the interference of the lander vibration and its reflection from an interface similar to 200 m below the lander generate the 3.3 Hz spectral peak and similar to 1.3 s arrival in the ACFs. The driving mechanism of the resolved dt/t thatmost likely explains the similar to 50min delay is thermoelastic strain at a near-surface layer, affecting the lander-ground coupling and subsurface structures. The two outlined mechanisms suggest, respectively, up to similar to 10% changes in ground stiffness at 1-5 Hz and similar to 15% velocity changes in the top similar to 20 m layer. These are upper bound values considering also other possible contributions. The presented methodology and results contribute to analysis of ACFs with limited data and the understanding of subsurface materials on Mars.