A document by Sebastián Carrasco. Click on the document to view its contents.

NASA InSight mission revealed that Mars is seismically active today and identified a region with high activity called Cerberus Fossae. Since then, the origin of marsquakes has been an important question in Mars seismology. On 2022/05/04, InSight seismometer detected the largest marsquake during the mission, named S1222a. The source was estimated to be outside the Cerberus Fossae and it would be important to constrain the source parameters of this remarkable event. In this study, we estimate the source parameters of S1222a through spectral analyses. Since we found that seismic spectra of S1222a are heavily contaminated, we performed Empirical Green’s Function analyses. We found that the corner frequencies are 0.34-0.54 Hz for the P wave and 0.17-0.24 Hz for the S wave. These values are slightly higher than those of seismic events at Cerberus Fossae, which implies a faster rupture at the source and different origin for S1222a.

The properties of the first kilometers of the Martian atmospheric Planetary Boundary Layer have until now been measured by only a few instruments and probes. InSight offers an opportunity to investigate this region through seismoacoustics. On six occasions, its seismometers recorded short low-frequency waveforms, with clear dispersion between 0.4 and 4Hz. These signals are the air-to-ground coupling of impact-generated infrasound, which propagated in an low-altitude atmospheric waveguide. Their group velocity depends on the structure of effective sound speed in the boundary layer. Here, we conduct a Bayesian inversion of effective sound speed up to 2000m altitude using the group velocity measured for events S0981c, S0986c and S1034a. The inverted effective sound speed profiles are in good agreement with estimates provided by the Mars Climate Database. Differences between inverted and modeled profiles can be attributed to a local wind variation in the impact → station direction, of amplitude smaller than 2m/s.

NASA’s InSight mission records several high-frequency (>0.5 Hz) dispersive seismic signals. These signals are due to the acoustic-to-seismic coupling, where the infrasound is generated by meteorite entry and impacts. This dispersion property is due to infrasound propagating in a structured atmosphere, and we refer to this infrasound as guided infrasound. We propose to model the propagation of guided infrasound and the seismic coupling to the ground analytically; we use a 1D layered atmosphere on a three-layer solid subsurface medium. The synthetic ground movements fit the observed dispersive seismic signals well. We also examine and validate the previously-published subsurface models derived from the InSight ambient seismic vibration data.