Autocorrelation of the ground vibrations recorded by the SEIS-InSight
seismometer on Mars
Abstract
The SEIS seismometer of the InSight mission was deployed on the ground
of Elysium Planitia, on 19 December 2018. Interferometry techniques can
be used to extract information on the internal structure from the
autocorrelation of seismic ambient noise and coda of seismic events. In
a single-station configuration, the zero-offset global reflection of the
ground vertically below the seismometer can be approximated by the
stacked ZZ autocorrelation function (ACF) for P-waves and the stacked EE
and NN ACFs for S-waves, assuming a horizontally layered medium and
homogeneously distributed and mutually uncorrelated noise sources. We
analyze continuous records from the very broadband seismometer
(SEIS-VBB), and correct for potential environmental disturbances through
systematic preprocessing. For each Sol (martian day), we computed the
correlations functions in 24 windows of one martian hour in order to
obtain a total correlation tensor for various Mars local times. In
addition, a similar algorithm is applied to the Marsquake waveforms in
different frequency bands. Both stability analysis and inter-comparison
between background noise and seismic event results suggest that the
background seismic noise at the landing site is reliably observed only
around 2.4 Hz, where an unknown mechanism is amplifying the ground
shaking, and only during early night hours, when the noise induced by
atmospheric disturbances is minimum. Seismic energy arrivals are
consistently observed across the various data-sets. Some of these
arrivals present multiples. These observations are discussed in terms of
Mars’ crustal structure.