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Published January 2018 | Supplemental Material + Published
Journal Article Open

Expected seismicity and the seismic noise environment of Europa


Seismic data will be a vital geophysical constraint on internal structure of Europa if we land instruments on the surface. Quantifying expected seismic activity on Europa both in terms of large, recognizable signals and ambient background noise is important for understanding dynamics of the moon, as well as interpretation of potential future data. Seismic energy sources will likely include cracking in the ice shell and turbulent motion in the oceans. We define a range of models of seismic activity in Europa's ice shell by assuming each model follows a Gutenberg-Richter relationship with varying parameters. A range of cumulative seismic moment release between 10^(16) and 10^(18) Nm/yr is defined by scaling tidal dissipation energy to tectonic events on the Earth's moon. Random catalogs are generated and used to create synthetic continuous noise records through numerical wave propagation in thermodynamically self-consistent models of the interior structure of Europa. Spectral characteristics of the noise are calculated by determining probabilistic power spectral densities of the synthetic records. While the range of seismicity models predicts noise levels that vary by 80 dB, we show that most noise estimates are below the self-noise floor of high-frequency geophones but may be recorded by more sensitive instruments. The largest expected signals exceed background noise by ∼50 dB. Noise records may allow for constraints on interior structure through autocorrelation. Models of seismic noise generated by pressure variations at the base of the ice shell due to turbulent motions in the subsurface ocean may also generate observable seismic noise.

Additional Information

© 2017 American Geophysical Union. Received 4 MAY 2017; Accepted 14 AUG 2017; Accepted article online 30 NOV 2017; Published online 25 JAN 2018. The authors acknowledge computational support in the project pr63qo "3-D wave propagation and rupture: forward and inverse problem" at Leibniz-Rechenzentrum Garching. S. C. S. was supported by grant SI1538/4-1 of Deutsche Forschungsgemeinschaft DFG. This work was partially supported by strategic research and technology funds from the Jet Propulsion Laboratory, Caltech and by the Icy Worlds node of NASA's Astrobiology Institute (13-13NAI7_2-0024). Noise waveform records and seismic catalogs are available via GitHub at http://github.com/mpanning/EuropaNoise. Axisem waveform databases are maintained by S. C. S. and can be accessed for use in Instaseis scripts via http://instaseis.ethz.ch/icy_ocean_worlds/. Sound files in the supporting information were created with Matlab scripts from Zhigang Peng (http://geophysics.eas.gatech.edu/people/zpeng/EQ_Music/). Work by M. P. was started at the University of Florida and was completed at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not constitute or imply its endorsement by the United States Government or the Jet Propulsion Laboratory, California Institute of Technology.

Attached Files

Published - Panning_et_al-2018-Journal_of_Geophysical_Research__Planets.pdf

Supplemental Material - 2017JE005332-sup-0001-Text_SI-S01_AA.pdf

Supplemental Material - 2017JE005332-sup-0002-Movie_SI-S01_AA.wav

Supplemental Material - 2017JE005332-sup-0003-Movie_SI-S02_AA.wav

Supplemental Material - 2017JE005332-sup-0004-Movie_SI-S03_AA.wav


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