Search

The most distant marsquake recorded so far by the InSight seismometer occurred at an epicentral distance of 146.3 ± 6.9o, close to the western end of Valles Marineris. On the seismogram of this event, we have identified seismic wave precursors, i.e., underside reflections off a subsurface discontinuity halfway between the marsquake and the instrument, which directly constrain the crustal structure away (about 4100-4500 km) from the InSight landing site. Here we show that the Martian crust at the bounce point between the lander and the marsquake is characterized by a discontinuity at about 20 km depth, similar to the second (deeper) intra-crustal interface seen beneath the InSight landing site. We propose that this 20-km interface, first discovered beneath the lander, is not a local geological structure but likely a regional or global feature, and is consistent with a transition from porous to non-porous Martian crustal materials.

The Seismic Experiment for Interior Structure (SEIS) of the InSight mission to Mars, has been providing direct information on Martian interior structure and dynamics of that planet since it landed. Compared to seismic recordings on Earth, ground motion measurements acquired by SEIS on Mars are made under dramatically different ambient noise conditions, but include idiosyncratic signals that arise from coupling between different InSight sensors and spacecraft components. This work is to synthesize what is known about these signal types, illustrate how they can manifest in waveforms and noise correlations, and present pitfalls in structural interpretations based on standard seismic analysis methods. We show that glitches, a type of prominent transient signal, can produce artifacts in ambient noise correlations. Sustained signals that vary in frequency, such as lander modes which are affected by variations in temperature and wind conditions over the course of the Martian Sol, can also contaminate ambient noise results. Therefore, both types of signals have the potential to bias interpretation in terms of subsurface layering. We illustrate that signal processing in the presence of identified nonseismic signals must be informed by an understanding of the underlying physical processes in order for high fidelity waveforms of ground motion to be extracted. While the origins of most idiosyncratic signals are well understood, the 2.4 Hz resonance remains debated and the literature does not contain an explanation of its fine spectral structure. Even though the selection of idiosyncratic signal types discussed in this paper may not be exhaustive, we provide guidance on best practices for enhancing the robustness of structural interpretations.

The analysis of seismic events recorded by NASA's InSight seismometer remains challenging, given their commonly low magnitudes and large epicentral distances, and concurrently, strongly varying background noise. These factors collectively result in low signal-to-noise ratios (SNR) across most event recordings. We use a deep learning denoising approach to mitigate the noise contamination, aiming to enhance the data analysis and the seismic event catalogue. Our systematic tests demonstrate that denoising performs comparable to fine-tuned bandpass filtering at high SNRs, but clearly outperforms it at low SNRs with respect to accurate waveform and amplitude retrieval, as well as onset picking. We review the denoised waveform data of all 98 low-frequency events in the Marsquake Service catalogue version 14, and improve their location when possible through the identification of phase picks and backazimuths, while ensuring consistency with the raw data. We demonstrate that several event waveforms can be explained by marsquake doublets—two similarly strong quakes in spatio-temporal proximity that result in overlapping waveforms at InSight—and we locate them in Cerberus Fossae (CF). Additionally, we identify and investigate aftershocks and an event sequence consisting of numerous relatively high magnitude marsquakes occurring within hours at epicentral distances beyond CF. As a result of this review and interpretation, we extend the catalogue in event numbers (⁠|$+$| 8 per cent), in events with epicentral distances and magnitudes (⁠|$+$| 50 per cent), and events with backazimuths and a resulting full locations (⁠|$+$| 46 per cent), leading to a more comprehensive description of Martian seismicity. [ABSTRACT FROM AUTHOR]

The Seismic Experiment for Interior Structure (SEIS) of the InSight mission to Mars has been providing direct information on Martian interior structure and dynamics of that planet since it landed. Compared with seismic recordings on the Earth, ground-motion measurements acquired by SEIS on Mars are not only made under dramatically different ambient noise conditions, but also include idiosyncratic signals that arise from coupling between different InSight sensors and spacecraft components. This work is to synthesize what is known about these signal types, illustrate how they can manifest in waveforms and noise correlations, and present pitfalls in structural interpretations based on standard seismic analysis methods. We show that glitches (a type of prominent transient signal) can produce artifacts in ambient noise correlations. Sustained signals that vary in frequency, such as lander modes that are affected by variations in temperature and wind conditions over the course of the Martian sol, can also contaminate ambient noise results. Therefore, both types of signals have the potential to bias interpretation in terms of subsurface layering. We illustrate that signal processing in the presence of identified nonseismic signals must be informed by an understanding of the underlying physical processes in order for high-fidelity waveforms of ground motion to be extracted. Whereas the origins of the most idiosyncratic signals are well understood, the 2.4 Hz resonance remains debated, and the literature does not contain an explanation of its fine spectral structure. Even though the selection of idiosyncratic signal types discussed in this article may not be exhaustive, we provide guidance on the best practices for enhancing the robustness of structural interpretations. [ABSTRACT FROM AUTHOR]

Seismic observations of impacts on Mars indicate a higher impact flux than previously measured. Using six confirmed seismic impact detections near the NASA InSight lander and two distant large impacts, we calculate appropriate scalings to compare these rates with lunar-based chronology models. We also update the impact rate from orbital observations using the most recent catalog of new craters on Mars. The snapshot of the current impact rate at Mars recorded seismically is higher than that found using orbital detections alone. The measured rates differ between a factor of 2 and 10, depending on the diameter, although the sample size of seismically detected impacts is small. The close timing of the two largest new impacts found on Mars in the past few decades indicates either a heightened impact rate or a low-probability temporal coincidence, perhaps representing recent fragmentation of a parent body. We conclude that seismic methods of detecting current impacts offer a more complete dataset than orbital imaging. [ABSTRACT FROM AUTHOR]