The seismic activity of a planet can be described by the corner magnitude, events larger than which are extremely unlikely, and the seismic moment rate, the long-term average of annual seismic moment release. Marsquake S1222a proves large enough to be representative of the global activity of Mars and places observational constraints on the moment rate. The magnitude-frequency distribution of relevant Marsquakes indicates a b-value of 1.17, but with its uncertainty and a volcanic region bias, b=1 is still possible. The moment rate is likely between 1.5e15 Nm/a and 1.6e18 Nm/a, with a marginal distribution peaking at 4.9e16 Nm/a. Comparing this with pre-InSight estimations shows that these tended to overestimate the moment rate, and that 30 % or more of the tectonic deformation may occur silently, whereas the seismicity is probably restricted to localized centers rather than spread over the entire planet.

The instrument package SEIS (Seismic Experiment for Internal Structure) with the three very broadband and three short-period seismic sensors is installed on the surface on Mars as part of NASA’s InSight Discovery mission. When compared to terrestrial installations, SEIS is deployed in a very harsh wind and temperature environment that leads to inevitable degradation of the quality of the recorded data. One ubiquitous artifact in the raw data is an abundance of transient one-sided pulses often accompanied by high-frequency spikes. These pulses, which we term “glitches”, can be modeled as the response of the instrument to a step in acceleration, while the spikes can be modeled as the response to a simultaneous step in displacement. We attribute the glitches primarily to SEIS-internal stress relaxations caused by the large temperature variations to which the instrument is exposed during a Martian day. Only a small fraction of glitches correspond to a motion of the SEIS package as a whole caused by minuscule tilts of either the instrument or the ground. In this study, we focus on the analysis of the glitch+spike phenomenon and present how these signals can be automatically detected and removed from SEIS’ raw data. As glitches affect many standard seismological analysis methods such as receiver functions, spectral decomposition and source inversions, we anticipate that studies of the Martian seismicity as well as studies of Mars’ internal structure should benefit from deglitched seismic data.

The InSight mission (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) has been collecting high-quality seismic data from Mars since February 2019, shortly after its landing. The Marsquake Service (MQS) is the team responsible for the prompt review of all seismic data recorded by the InSight’s seismometer (SEIS), marsquake event detection, and curating seismicity catalogues. Until sol 1011 (end of September 2021), MQS have identified 951 marsquakes that we interpret to occur at regional and teleseismic distances, and 1062 very short duration events that are most likely generated by local thermal stresses nearby the SEIS package. Here, we summarize the seismic data collected until sol 1011, version 9 of the InSight seismicity catalogue. We focus on the significant seismicity that occurred after sol 478, the end date of version 3, the last catalogue described in a dedicated paper. In this new period, almost a full Martian year of new data has been collected, allowing us to observe seasonal variations in seismicity that are largely driven by strong changes in atmospheric noise that couples into the seismic signal. Further, the largest, closest and most distant events have been identified, and the number of fully located events has increased from 3 to 7. In addition to the new seismicity, we document improvements in the catalogue that include the adoption of InSight-calibrated Martian models and magnitude scales, the inclusion of additional seismic body-wave phases, and first focal mechanism solutions for three of the regional marsquakes at distances ~30 degrees.

The InSight mission [1] landed in November 2018 in the Elysium Planitia region [2] bringing the first geophysical observatory to Mars. Since February 2019 the seismometer SEIS [3] has continuously recorded Mars’ seismic activity, and a list of the seismic events is available in the InSight Marsquake Service catalog [4]. In this study, we predict present-day seismic velocities in the Martian interior using the 3D thermal evolution models of [5]. We then use the 3D velocity distributions to interpret seismic observations recorded by InSight. Our analysis is focused on the two high quality events S0173a and S0235b. Both have distinguishable P- and S-wave arrivals and are thought to originate in Cerberus Fossae [6], a potentially active fault system [7]. Our results show that models with a crust containing more than half of the total amount of heat producing elements (HPE) of the bulk of Mars lead to large variations of the seismic velocities in the lithosphere. A seismic velocity pattern similar to the crustal thickness structure is observed at depths larger than 400 km for cases with cold and thick lithospheres. Models, with less than 20% of the total HPE in the crust have thinner lithospheres with shallower but more prominent low velocity zones. The latter, lead to shadow zones that are incompatible with the observed P- and S-wave arrivals of seismic events occurring in Cerberus Fossae, in 20° - 40° epicentral distance. We therefore expect that future high-quality seismic events have the potential to further constrain the amount of HPE in the Martian crust. Future work will combine the seismic velocities distribution calculated in this study with modeling of seismic wave propagation [8, 9]. This will help to assess the effects of a 3D thermal structure on the waveforms and provide a powerful framework for the interpretation of InSight’s seismic data. [1] Banerdt et al., Nat. Geo. 2020; [2] Golombek et al., Nat. Comm. 2020, [3] Lognnoné et al., Nat. Geo. 2020, [4] InSight MQS, Mars Seismic Catalogue, InSight Mission V3, 2020, https://doi.org/10.12686/A8, [5] Plesa et al., GRL 2018, [6] Giardini et al., Nat. Geo. 2020, [7] Taylor et al., JGR 2013, [8] Bozdag et al., SSR 2017, [9] Komatitsch & Tromp, GJI 2002.