Characteristics of Horizontal to Vertical Spectral Ratio of InSight Seismic Data From Mars

Abstract

AbstractSince February 2019, the InSight mission has returned seismic and meteorological data from Mars. We conducted horizontal to vertical spectral ratio (HVSR) analysis to the InSight seismic data recorded both on the lander and on the ground. Horizontal to vertical spectral ratio curves of ground data show multi‐peak characteristics at frequencies between 1 and 30 Hz with the highest peak appearing at around 11.7 Hz. The HVSR results of the Very Broad Band (VBB) and Short Period (SP) data differ greatly for frequencies over 10 Hz due to the difference in vertical component. The onboard SP data have the same highest H/V peak as the ground SP data. We conducted numerical modeling of HVSR and confirmed that the wind‐induced lander vibrations are the major sources to the InSight seismic ground motion in high frequencies. The HVSR curves of the continuous ground SEIS data show diurnal variation and are highly correlated with local meteorological conditions. The particle motions are investigated through the polarization analysis and the random decrement method. Generally, the ground motions above the self‐noise level are linearly polarized in the horizontal plane around the highest H/V peak. The damping analysis demonstrated the mechanical origins of the highest HVSR peak, while the 2.4 Hz mode is the most likely one having natural origin. Finally, most marsquake signals analyzed in this study generally highlight the 2.4 Hz trough but cause no significant change on the shape of the H/V curves. Our study explores the possible existence of natural sources in relatively high frequencies of Mars' background noise.