Auto-correlation of the Seismic Ambient Noise Recorded by SEIS, the Seismometer of the InSight Mission on Mars.

AGU Fall Meeting 2019 in San Francisco, 9-13 December 2019Since the two seismometers of the InSight mission have been dropped on the ground of the landing site at Elysium Planitia on December, 2018 more than 200 martian days (called SOL) of seismic record have been repatriated on Earth. With a long enough continuous seismic signal the application of seismic interferometry techniques can be considered to extract information on the shallows structures or the elastic properties of the medium from auto-correlation of seismic ambient noise. In single-station configuration the zero-offset global reflection response at the vertical of the seismometer can be approximated by the stacked Z-Z auto-correlation function for P-waves velocity and the stacked E-E and N-N auto-correlations functions for S-waves velocity, assuming a perfectly vertical layered medium and homogeneously distributed and mutually uncorrelated noise sources. As good signal-to-noise ratios are needed to apply this kind of analysis we experiment various pre-processing approaches before the computation of the correlations functions and try to take into account all the potentials disturbances coming from the lander¿s modes or the various artificial signals in the data. We focused our analysis on a continuous 10sps-very-broadband (VBB) record. In each SOL we computed the correlations functions in 24 windows of one martian hour duration in order to obtain a total correlation tensor for various Mars time. Finally we applied a time-frequency adaptive method to filter the incoherent phase arrivals. Potential interpretation of the retrieved auto-correlations to the crustal structure of Mars and its temporal variations will be discussed.ag