Abstract
Mars is the first extraterrestrial planet with seismometers (SEIS)
deployed directly on its surface in the framework of the InSight
(Interior Exploration using Seismic Investigations, Geodesy and Heat
Transport) mission. The lack of strong Marsquakes, however, strengthens
the need of seismic noise studies to additionally constrain the Martian
structure. Seismic noise autocorrelations of single-station recordings
permit the determination of the zero-offset reflection response
underneath SEIS. We present a new autocorrelation study which employs
state-of-the-art approaches to determine a robust reflection response by
avoiding bias from aseismic signals which are recorded together with
seismic waves due to unfavorable deployment and environmental
conditions. Data selection and segmentation is performed in a
data-adaptive manner which takes the data root-mean-square amplitude
variability into account. We further use the amplitude-unbiased phase
cross-correlation and work in the 1.2-8.9 Hz frequency band. The main
target are crustal scale reflections, their robustness and convergence.
The strongest signal appears at 10.6 s, and, if interpreted as P-wave
reflection, would correspond to a discontinuity at about 24 km depth.
This signal is a likely candidate for a reflection from the base of the
Martian crust due to its strength, polarity, and stability. Additionally
we identify, among the stable signals, a signal at about 6.85 s that can
be interpreted as a P-wave reflection from the mid-crust at about 9.5 km
depth.