Browsing by Author "Charalambous, C."

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    First observations of core-transiting seismic phases on Mars
    Irving, J. C. E.; Lekic, V.; Durán, C.; Drilleau, M.; Kim, D.; Rivoldini, A.; Khan, A.; Samuel, H.; Antonangeli, D.; Bruce Banerdt, W.; Beghein, C.; Bozdagk, E.; Ceylan, S.; Charalambous, C.; Clinton, J.; Davis, P.; Garcia, R.; Giardini, D.; Catherine Horleston, A.; Huang, Q.; Hurst, K. J.; Kawamura, T.; King, Scott D.; Knapmeyer, M.; Li, J.; Lognonné, P.; Maguire, Ross; Panning, M. P.; Plesa, A. C.; Schimmel, M.; Schmerr, N. C.; Stählerc, S. C.; Stutzmann, E.; Xu, Z. (Proceedings of the National Academy of Sciences, 2023-05-02)
    We present the first observations of seismic waves propagating through the core of Mars. These observations, made using seismic data collected by the InSight geophysical mission, have allowed us to construct the first seismically constrained models for the elastic properties of Mars core. We observe core-Transiting seismic phase SKS from two farside seismic events detected on Mars and measure the travel times of SKS relative to mantle traversing body waves. SKS travels through the core as a compressional wave, providing information about bulk modulus and density. We perform probabilistic inversions using the core-sensitive relative travel times together with gross geophysical data and travel times from other, more proximal, seismic events to seek the equation of state parameters that best describe the liquid iron-Alloy core. Our inversions provide constraints on the velocities in Mars core and are used to develop the first seismically based estimates of its composition. We show that models informed by our SKS data favor a somewhat smaller (median core radius = 1,780 to 1,810 km) and denser (core density = 6.2 to 6.3 g/cm3) core compared to previous estimates, with a P-wave velocity of 4.9 to 5.0 km/s at the core mantle boundary, with the composition and structure of the mantle as a dominant source of uncertainty. We infer from our models that Mars core contains a median of 20 to 22 wt% light alloying elements when we consider sulfur, oxygen, carbon, and hydrogen. These data can be used to inform models of planetary accretion, composition, and evolution.
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    Machine learning and marsquakes: a tool to predict atmospheric-seismic noise for the NASA InSight mission
    Stott, A. E.; Garcia, R. F.; Chedozeau, A.; Spiga, A.; Murdoch, N.; Pinot, B.; Mimoun, D.; Charalambous, C.; Horleston, A.; King, Scott D.; Kawamura, T.; Dahmen, N.; Barkaoui, S.; Lognonne, P.; Banerdt, W. B. (Oxford University Press, 2023-01-04)
    The SEIS (seismic experiment for the interior structure of Mars) experiment on the NASA InSight mission has catalogued hundreds of marsquakes so far. However, the detectability of these events is controlled by the weather which generates noise on the seismometer. This affects the catalogue on both diurnal and seasonal scales. We propose to use machine learning methods to fit the wind, pressure and temperature data to the seismic energy recorded in the 0.4–1 and 2.2–2.6 Hz bandwidths to examine low- (LF) and high-frequency (HF) seismic event categories respectively. We implement Gaussian process regression and neural network models for this task. This approach provides the relationship between the atmospheric state and seismic energy. The obtained seismic energy estimate is used to calculate signal-to-noise ratios (SNR) of marsquakes for multiple bandwidths. We can then demonstrate the presence of LF energy above the noise level during several events predominantly categorized as HF, suggesting a continuum in event spectra distribution across the marsquake types. We introduce an algorithm to detect marsquakes based on the subtraction of the predicted noise from the observed data. This algorithm finds 39 previously undetected marsquakes, with another 40 possible candidates. Furthermore, an analysis of the detection algorithm’s variable threshold provides an empirical estimate of marsquake detectivity. This suggests that events producing the largest signal on the seismometer would be seen almost all the time, the median size signal event 45–50 per cent of the time and smallest signal events 5−20 per cent of the time.
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    Surface waves and crustal structure on Mars
    Kim, D.; Banerdt, W. B.; Ceylan, S.; Giardini, D.; Lekic, V.; Lognonne, P.; Beghein, C.; Beucler, E.; Carrasco, S.; Charalambous, C.; Clinton, J.; Drilleau, M.; Duran, C.; Golombek, M.; Joshi, R.; Khan, A.; Knapmeyer-Endrun, B.; Li, J.; Maguire, Ross; Pike, W. T.; Samuel, H.; Schimmel, M.; Schmerr, N. C.; Stahler, S. C.; Stutzmann, E.; Wieczorek, M.; Xu, Z.; Batov, A.; Bozdag, E.; Dahmen, N.; Davis, P.; Gudkova, T.; Horleston, A.; Huang, Q.; Kawamura, T.; King, Scott D.; McLennan, S. M.; Nimmo, F.; Plasman, M.; Plesa, A. C.; Stepanova, I. E.; Weidner, E.; Zenhausern, G.; Daubar, I. J.; Fernando, B.; Garcia, R. F.; Posiolova, L.; Panning, M. P. (AAAS, 2022-10-28)
    We detected surface waves from two meteorite impacts on Mars. By measuring group velocity dispersion along the impact-lander path, we obtained a direct constraint on crustal structure away from the InSight lander. The crust north of the equatorial dichotomy had a shear wave velocity of approximately 3.2 kilometers per second in the 5- to 30-kilometer depth range, with little depth variation. This implies a higher crustal density than inferred beneath the lander, suggesting either compositional differences or reduced porosity in the volcanic areas traversed by the surface waves. The lower velocities and the crustal layering observed beneath the landing site down to a 10-kilometer depth are not a global feature. Structural variations revealed by surface waves hold implications for models of the formation and thickness of the martian crust.