Seismic observations involve signals that can be easily masked by noise injection. For InSight, NASA's lander on Mars, the atmosphere is a significant noise contributor for two thirds of a Martian day, and while the noise is below that seen at even the quietest sites on Earth, the amplitude of seismic signals on Mars is also considerably lower requiring an understanding and quantification of environmental injection at unprecedented levels. Mars' ground and atmosphere provide a continuous coupled seismic system, and although atmospheric functions are of distinct origins, the superposition of these noise contributions is poorly understood, making separation a challenging task. We present a novel method for partitioning the observed signal into seismic and environmental contributions. Pressure and wind fluctuations are shown to exhibit temporal cross-frequency coupling across multiple bands, injecting noise that is neither random nor coherent. We investigate this through comodulation, quantifying the signal synchrony in seismic motion, wind and pressure. By working in the time-frequency domain, we discriminate the origins of underlying processes and provide the site's environmental sensitivity. Our method aims to create a virtual vault at InSight, shielding the seismometers with effective post-processing in lieu of a physical vault. This allows us to describe the environmental and seismic signals over a sequence of sols, to quantify the wind and pressure injection, and estimate the seismic content of possible Marsquakes with a signal-to-noise ratio that can be quantified in terms of environmental independence. Finally, we exploit the temporal energy correlations for source attribution of our observations.

The NASA InSight mission to Mars successfully landed on November 26th, 2018 in Elysium Planitia. It aims to characterize the seismic activity and constrain the internal structure of Mars. We focus on the Cerberus Fossae region, a giant fracture network of ~1200 km long situated east of the InSight landing site, and where M~3 marsquakes were detected during the past two years. It is formed of five main fossae located on the southeast of the Elysium Mons volcanic rise. We perform a detailed mapping of the entire system based on high resolution satellite images and Digital Elevation Models. The refined cartography reveals a range of morphologies associated with dike activities at depth. Width and throw measurements of the fossae are linearly correlated, suggesting a possible tectonic control on the shapes of the fossae. Widths and throws decrease toward the east, indicating the long-term direction of propagation of the dike-induced graben system. They also give insights into the geometry at depth and how the possible faults and fractures are rooted in the crust. The exceptional preservation of the fossae allows us to detect up to four scales of segmentation, each formed by a similar number of 3-4 segments/subsegments. This generic distribution is comparable to continental faults and fractures on Earth. We anticipate higher stress and potential for marsquakes within intersegment zones and at graben tips.

In early 2019, NASA’s InSight lander successfully deployed a single three-component very broadband seismometer (VBB) on the surface of Mars to detect and characterize marsquakes. Using these data, we present a method to infer the source mechanisms of marsquakes from waveforms of P and S waves recorded at a single station. We show that the three events with the highest signal-to-noise ratio (SNR) and a robust distance estimate S0173a, (May 23rd 2019), S0235b, (July 27th 2019) and S0183a, (June 3rd 2019) are all likely the results of normal faulting, suggesting an extensional regime mainly oriented south-east north-west in the respective source regions, Cerberus Fossae and Orcus Patera. We quantify the uncertainty of our solutions by comparing results of a direct inversion with a grid-search method.

The SEIS seismometer deployed at the surface of Mars in the framework of the NASA-InSight mission has been continuously recording the ground motion at Elysium Planitia for more than one martian year. In this work, we investigate the seasonal variation of the near surface properties using both background vibrations and a particular class of high-frequency seismic events. We present measurements of relative velocity changes over one martian year and show that they can be modeled by a thermoelastic response of the Martian regolith. Several families of high-frequency seismic multiplets have been observed at various periods of the martian year. These events exhibit repeatable waveforms with an emergent character and a coda that is likely composed of scattered waves. Taking advantage of these properties, we use coda waves interferometry to measure relative travel-time changes as a function of the date of occurrence of the quakes. While in some families a stretching of the coda waveform is clearly observed, in other families we observe either no variation or a clear contraction of the waveform. Measurements of velocity changes from the analysis of background vibrations above 5Hz are consistent with the results from coda wave interferometry. We identify a frequency band structure in the power spectral density, that can be tracked over hundreds of days. This band structure is the equivalent in the frequency domain of an autocorrelogram and can be efficiently used to measure relative travel-time changes as a function of frequency. The observed velocity changes can be adequately modeled by the thermoelastic response of the regolith to the time-dependent incident solar flux at the seasonal scale. In particular, the model captures the time delay between the surface temperature variations and the velocity changes in the sub-surface. Our observations could serve as a basis for a joint inversion of the seismic and thermal properties in the first meters below InSIght.

Orbital and surface observations demonstrate that aeolian activity is occurring on Mars. Here we report the aeolian changes observed in situ by NASA's InSight lander during the first 400 sols of operations. Aeolian changes include creep of grains with diameters of up to 3 mm, dust removal, dark trails left by passing vortices and possible saltation. InSight has observed such changes by using, for the first time, simultaneous imaging and continuous, high-frequency meteorological, seismological, and magnetic measurements. We show that this multi-instrument combination constrains both the timing, and specific atmospheric conditions during which, aeolian changes occur. The observed changes are infrequent and episodic, consistently occur between noon and 3 pm, and are systematically associated with the passage of convective vortices. The sudden onset of peak vortex wind speeds promotes particle motion during sequences of enhanced vortex activity and stronger ambient winds. Aeolian changes are correlated with excursions in ground acceleration and magnetic field strength, suggesting vortex-induced ground deformation and charged-particle motion.

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.

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.

Since landing on Mars, the NASA InSight lander has witnessed 8 Phobos and one Deimos transit. All transits could be observed by a drop in the solar array current and the surface temperature, but more surprisingly, for several ones, a clear signature was recorded with the seismic sensors and the magnetometer. We present a preliminary interpretation of the seismometer data as temperature induced local deformation of the ground, supported by terrestrial analog experiments and finite-element modelling. The magnetic signature is most likely induced by changing currents from the solar arrays. While the observations are not fully understood yet, the recording of transit-related phenomena with high sampling rate will allow more precise measurements of the transit times, thus providing additional constraints for the orbital parameters of Phobos. The response of the seismometer can potentially also be used to constrain the thermo-elastic properties of the shallow regolith at the landing site.

The NASA InSight lander successfully placed a seismometer on the surface of Mars. Alongside, a hammering device was deployed that penetrated into the ground to attempt the first measurements of the planetary heat flow of Mars. The hammering of the heat probe generated repeated seismic signals that were registered by the seismometer and can potentially be used to image the shallow subsurface just below the lander. However, the broad frequency content of the seismic signals generated by the hammering extends beyond the Nyquist frequency governed by the seismometer's sampling rate of 100 samples per second. Here, we propose an algorithm to reconstruct the seismic signals beyond the classical sampling limits. We exploit the structure in the data due to thousands of repeated, only gradually varying hammering signals as the heat probe slowly penetrates into the ground. In addition, we make use of the fact that repeated hammering signals are sub-sampled differently due to the unsynchronised timing between the hammer strikes and the seismometer recordings. This allows us to reconstruct signals beyond the classical Nyquist frequency limit by enforcing a sparsity constraint on the signal in a modified Radon transform domain. Using both synthetic data and actual data recorded on Mars, we show how the proposed algorithm can be used to reconstruct the high-frequency hammering signal at very high resolution. In this way, we were able to constrain the seismic velocity of the top first meter of the Martian regolith.