The seismicity of Mars

Abstract

ol 185 was a typical sol on Mars (a Mars sol is 24 h 39.5 min long, and we number sols starting from landing). The ground acceleration spectrogram recorded by the very broadband (VBB) instrument of SEIS 1-3 (Seismic Experiment for Interior Structure; Fig. 1a) is dominated by the noise produced by the weakly turbulent night-time winds and by the powerful, thermally driven convective turbulence during the day 4. Around 17:00 local mean solar time (lmst), the wind fluctuations die out quite suddenly and the planet remains very quiet into the early night hours. Several distinctive features can be seen every sol on Mars. Lander vibrations activated by the wind appear as horizontal thin lines with frequency varying daily as a result of temperature variations of the lander; almost invisible during quiet hours, they are not excited by seismic events (for example, the lander mode at 4 Hz in Fig. 1a). We also observe a pronounced ambient resonance at 2.4 Hz, strongest on the vertical component, with no clear link to wind strength but excited by all the seismic vibrations at that frequency. The relative excitations of the 2.4 Hz and 4 Hz modes serve as discriminants for the origin of ground vibrations recorded by SEIS, allowing us to distinguish between local vibrations induced by atmospheric or lander activity and more distant sources of ground vibrations. On Sol 185, two weak events can also be spotted in the quiet hours of the early evening, one with a broadband frequency content and a second 80 min later, centred on the 2.4 Hz resonance band (Fig. 1a).

Constraints on the shallow elastic and anelastic structure of Mars from InSight seismic data

“…After each coherent arrival, the signal shows a coda with no characteristic polarization. The signal-to-noise ratios are higher than for S0128a and the events are located at roughly 1,720 km and 1,535 km distances 4 . This suggests seismic waves propagating in a relatively transparent but attenuating Martian mantle before entering the regional crustal structure beneath InSight.…”

“…1-10 and 1-11). None have surface waves, suggesting a depth too large to excite them above the noise and/ or surface-wave scattering 4 . Their high signal-to-noise ratio, particularly with respect to wind (Supplementary Discussion 1 and corresponding spectra, seismograms and wind/pressure records in Supplementary Figs.…”

Geology of the InSight landing site on Mars

“…Observed in the pits beneath the lander (8) and in the mole hole is a duricrust of cemented sand, pebbles and rocks that is 5-10 cm thick (shown in blue), but could vary in thickness. Beneath the duricrust are overlapping craters (4,5), rocks (7), and lens of ejecta from other craters (10). The relatively finegrained impact generated regolith (3) is around 3 m thick beneath the lander and likely grades with depth into coarse, blocky ejecta (2) that overlies fractured basalt flows (1).…”

“…1). Cerberus Fossae is among the youngest fault scarps on Mars with boulder trails attributed to paleomarsquakes 8 and seismic events that were expected 9 and have been observed by InSight 10 . Geologic mapping performed as part of the landing site selection process (prior to landing), indicates the plains beneath the lander (Fig.…”

NASA’s InSight mission on Mars—first glimpses of the planet’s interior from seismology

“…Initial analysis of converted phases in the seismograms of two quakes points to the first crustal layer of 8-11-km thickness with unexpectedly low velocities pointing to highly altered or fractured material 8 . The observation of low amplitudes of S waves in recordings from a specific distance range hints at a low-velocity zone in the Martian mantle, which was predicted by some, but not all, a priori models, and will help to constrain mineralogy 12 .…”