InSight’s Contributions to Planetary Seismology and Geophysics

After an auspicious beginning, with the Ranger, Apollo and Viking missions carrying multiple seismometers into space, planetary seismology lay dormant for 40 years, save for a cruelly-extinguished hope on the Mars’96 mission. InSight put an end to this seismological drought with its landing on Mars in November, 2018, and subsequent deployment of the SEIS instrument two months later (Banerdt et al., 2020; Lognonné et al., 2019, 2020).

After a slow start (uncannily, no seismic events were detected for the first two months after deployment), the subsequent three-plus years  have been an unqualified triumph for planetary seismology. Roughly 2700 seismic events have been detected and cataloged (Clinton et al., 2021; Ceylan et al., 2022), ranging from more than a thousand tiny SF events, thought to be locally-sourced thermal events, to a massive magnitude 5 marsquake more than 2000 km away, but still with a signal-to-noise ratio over 160,000. This catalog includes more than 30 Low Frequency and Broad-Band marsquake signals of quality A or B, meaning they have clear body-wave phase arrivals and, in the case of quality A, identifiable polarization. These have been clearly identified as teleseismic events, which taken together describe a set of ray paths that have probed the interior of the planet from the surface down to its core.

The analysis of this seismic data set has already transformed our knowledge of the interior structure of Mars. We have for the first time been able to directly measure the thickness of the crust beneath InSight (Knapmeyer-Endrun, et al., 2021; Kim et al., 2021; Durán et al., 2022; Drilleau et al., 2022) and the size of the martian core (Stähler et al., 2021). Analysis of the data has further allowed us to place tight constraints on the density of the core and crust, and the thermal profile of the mantle (Stähler et al., 2021; Khan et al., 2021, 2022; Wieczorek et al., 2022). In addition, SEIS’s observations have proved invaluable for studying the near-surface structure beneath InSight on scales from tens of centimeters to hundreds of meters (e.g., Lognonné et al., 2020; Banerdt et al., 2020; Kenda et al., 2020; Hobiger et al., 2021; Murdoch et al., 2021; Compaire et al., 2021, 2022).

InSight’s seismometer has also been able to study the current tectonics of Mars, providing a measure of the size distribution of seismic events (and thus a window into the rate of moment release) and a map of their geographic distribution (in particular, the strong concentration of Eastern hemisphere activity around Cerberus Fossae; Giardini et al., 2020; Stähler et al., 2022) and even revealing the source mechanisms responsible for some marsquakes, from which the orientation of stresses in the lithosphere can be inferred (Brinkman et al., 2021).

InSight and SEIS have proven conclusively the value of planetary seismology in general, and a single high-quality seismometer in particular, in understanding the solid planets of our solar system. The results described in this talk are only a subset of the work that has been done, and was derived from just the first round of analysis of SEIS data. As the seismic community becomes more familiar with the data set and it becomes more widely used, we can expect new insights into the geophysics of Mars for decades to come.

 

References:

Banerdt, W. B., and Smrekar, S. E., et al., 2020. Initial results from the InSight mission on Mars. Nat. Geosci. 13, 183–189. https://doi.org/10.1038/s41561-020-0544-y

Brinkman, N., et al., 2021. First focal mechanisms of marsquakes, J. Geophys. Res. Planets, e2020JE006546. https://doi.org/10.1029/2020JE006546

Ceylan, S., et al., 2022. The marsquake catalogue from InSight, sols 0-1011, Phys. Earth Planet. Int., in press.

Clinton, J., et al., 2021. The Marsquake Catalogue from InSight, Sols 0-478, Phys. Earth Planet. Int. 310, 106597. https://doi.org/10.1016/j.pepi.2020.106597

Compaire, N., et al., 2021. Autocorrelation of the ground vibrations recorded by the SEIS-InSight seismometer on Mars, J. Geophys. Res. Planets 126, e2020JE006498. https://doi.org/10.1029/2020JE006498

Compaire, N., et al., 2022. Seasonal variations of subsurface seismic velocities monitored by the SEIS-InSight seismometer on Mars, Geophys. J. Int. 229:2, 776–799. https://doi.org/10.1093/gji/ggab499

Drilleau, M., et al., 2022. Marsquake location and 1-D seismic models for Mars from InSight data, J. Geophys. Res. Planets, in press.

Durán, C., et al., 2022. Seismology on Mars: An analysis of direct, reflected, and converted seismic body waves with implications for interior structure, Phys. Earth Planet. Int., in press.

Hobiger, M., et al., 2021. The shallow structure of Mars from inversion of high-frequency ambient seismic vibrations Rayleigh wave ellipticity at the InSight landing site, Nat. Comm. 12, 6756,. https://doi.org/10.1038/s41467-021-26957-7

Kenda, B., et al., 2020. Subsurface structure at the InSight landing site from compliance measurements by seismic and meteorological experiments, J. Geophys. Res. Planets 125, 6, e2020JE006387. https://doi.org/10.1029/2020JE006387

Khan, A., et al., 2021. Upper mantle structure of Mars from InSight seismic data, Science, 373, 434-438. https://doi.org/10.1126/science.abf2966

Khan, A., et al., 2022. Geophysical and cosmochemical constraints on the bulk composition of Mars , Earth Planet. Sci. Lett. 578. https://doi.org/10.1016/j.epsl.2021.117330

Kim, D., et al., 2021. Improving constraints on planetary interiors with PPs receiver functions, J. Geophys. Res. Planets 126, e2021JE006983. https://doi.org/10.1029/2021JE006983

Knapmeyer-Endrun, B., et al., 2021. Thickness and structure of the martian crust from InSight seismic data, Science, 373, 438-443. https://doi.org/10.1126/science.abf8966

Lognonné, P., et al., 2020. Constraints on the shallow elastic and anelastic structure of Mars from InSight seismic data. Nat. Geosci. 13, 213–220. https://doi.org/10.1038/s41561-020-0536-y

Murdoch, N., et al., 2021. Constraining Martian regolith and vortex parameters from combined seismic and meteorological measurements, J. Geophys. Res. Planets 126, e2020JE006410. https://doi.org/10.1029/2020JE006410

Stähler, S. C., et al., 2021. Seismic detection of the martian core, Science, 373, 443-448. https://doi.org/10.1126/science.abi7730

Stähler, S., et al., 2022. Marsquakes indicate dike-induced tectonics in Cerberus Fossae, Mars, Nature Geoscience, in press.

Wieczorek, M., et al., 2022. InSight constraints on the global character of the Martian crust, J. Geophys. Res. Planets, e2022JE007298. https://doi.org/10.1029/2022JE007298