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Near-Field Seismic Propagation and Coupling Through Mars’ Regolith: Implications for the InSight Mission

Research output: Contribution to journalReview article

Original languageEnglish
Article number85
Number of pages24
JournalSpace Science Reviews
Volume214
Issue number5
Early online date9 Jul 2018
DOIs
DateAccepted/In press - 25 May 2018
DateE-pub ahead of print - 9 Jul 2018
DatePublished (current) - 1 Aug 2018

Abstract

NASA’s InSight Mission will deploy two three-component seismometers on Mars in 2018. These short period and very broadband seismometers will be mounted on a three-legged levelling system, which will sit directly on the sandy regolith some 2–3 meters from the lander. Although the deployment will be covered by a wind and thermal shield, atmospheric noise is still expected to couple to the seismometers through the regolith. Seismic activity on Mars is expected to be significantly lower than on Earth, so a characterisation of the extent of coupling to noise and seismic signals is an important step towards maximising scientific return. In this study, we conduct field testing on a simplified model of the seismometer assembly. We constrain the transfer function between the wind and thermal shield and tripod-mounted seismometers over a range of frequencies (1–40 Hz) relevant to the deployment on Mars. At 1–20 Hz the displacement amplitude ratio is approximately constant, with a value that depends on the site (0.03–0.06). The value of the ratio in this range is 25–50% of the value expected from the deformation of a homogeneous isotropic elastic halfspace. At 20–40 Hz, the ratio increases as a result of resonance between the tripod mass and regolith. We predict that mounting the InSight instruments on a tripod will not adversely affect the recorded amplitudes of vertical seismic energy, although particle motions will be more complex than observed in recordings generated by more conventional buried deployments. Higher frequency signals will be amplified by tripod-regolith resonance, probably reaching peak-amplification at ∼ 50 Hz. The tripod deployment will lose sensitivity at frequencies > 50 Hz as a result of the tripod mass and compliant regolith. We also investigate the attenuation of seismic energy within the shallow regolith covering the range of seismometer deployment distances. The amplitude of surface displacement decays as r n, where 1.5 < n< 2. This exceeds the value expected for a homogeneous isotropic elastic halfspace (n∼ 1), and reflects an increase in Young’s modulus with depth. We present an updated model of lander noise which takes this enhanced attenuation into account.

    Research areas

  • InSight, Mars, Transfer coefficient

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    Rights statement: This is the final published version of the article (version of record). It first appeared online via Springer at https://doi.org/10.1007/s11214-018-0514-5 . Please refer to any applicable terms of use of the publisher.

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    Rights statement: This is the final published version of the article (version of record). It first appeared online via Springer at https://doi.org/10.1007/s11214-018-0514-5 . Please refer to any applicable terms of use of the publisher.

    Final published version, 593 KB, PDF document

    Licence: CC BY

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