TY - JOUR
T1 - Constraining Europa's ice shell thickness with fundamental mode surface wave dispersion
AU - Maguire, Ross R.
AU - Schmerr, Nicholas C.
AU - Lekić, Vedran
AU - Hurford, Terry A.
AU - Dai, Lenore
AU - Rhoden, Alyssa R.
N1 - Funding Information:
We thank Mark Panning and an anonymous reviewer, as well as Editor-In-Cheif Rosaly Lopes, for helpful comments that have allowed us to improve this manuscript. RM and NS were supported by a NASA-COLDTECH grant # NNX17AF70G and NS also by NASA-PSTAR grant # 80NSSC17K0229 and NASA SSERVI GEODES grant #80NSSC19M0216 . Additionally, RM was supported in part by NSF postdoctoral fellowship Award # 1806412 .
Publisher Copyright:
© 2021 Elsevier Inc.
PY - 2021/11/15
Y1 - 2021/11/15
N2 - Determining the thickness of Europa's outer ice shell is a key factor for understanding Europa's internal dynamics, evolution, and potential habitability. As such, one of the primary goals of any future lander mission to Europa would be to constrain the thickness of the ice shell and confirm the presence of a global subsurface ocean. Tidally induced ice fracturing events provide a natural source of seismic energy to illuminate the subsurface, thus a seismic instrument onboard a future lander mission could provide a promising means to probe ice shell thickness. A variety of seismic techniques could be used to constrain Europa's interior structure and dynamics, including body wave, surface wave, and normal mode seismology. Here, we use numerical simulations of seismic wave propagation on Europa in order to investigate the potential of using long period dispersion measurements of Rayleigh and flexural waves to constrain the ice shell thickness. Since the sensitivity kernels of group velocity dispersion measurements depend strongly on the structure of the ice shell, inverting for ice shell thickness is a non-linear problem. To address this, we use either a grid search or Markov chain Monte Carlo inversion approach, and test the method on a variety of plausible models of Europa's interior. Additionally, we demonstrate our approach in a “blind” inversion using the 1 week long synthetic catalogs of Europa's seismicity from Panning et al. (2018). We find that under most scenarios, group velocity dispersion measurements between periods of 25–250 s can constrain Europa's ice shell thickness to within several km uncertainty, although the method becomes increasingly inaccurate for thicker ice shells and at large epicentral distances. Our results, which suggest that surface waves from naturally occurring ice fracturing events on Europa can be used to help determine ice shell thickness, may help set instrument requirements for spaceflight capable seismometers aimed at exploring icy ocean worlds.
AB - Determining the thickness of Europa's outer ice shell is a key factor for understanding Europa's internal dynamics, evolution, and potential habitability. As such, one of the primary goals of any future lander mission to Europa would be to constrain the thickness of the ice shell and confirm the presence of a global subsurface ocean. Tidally induced ice fracturing events provide a natural source of seismic energy to illuminate the subsurface, thus a seismic instrument onboard a future lander mission could provide a promising means to probe ice shell thickness. A variety of seismic techniques could be used to constrain Europa's interior structure and dynamics, including body wave, surface wave, and normal mode seismology. Here, we use numerical simulations of seismic wave propagation on Europa in order to investigate the potential of using long period dispersion measurements of Rayleigh and flexural waves to constrain the ice shell thickness. Since the sensitivity kernels of group velocity dispersion measurements depend strongly on the structure of the ice shell, inverting for ice shell thickness is a non-linear problem. To address this, we use either a grid search or Markov chain Monte Carlo inversion approach, and test the method on a variety of plausible models of Europa's interior. Additionally, we demonstrate our approach in a “blind” inversion using the 1 week long synthetic catalogs of Europa's seismicity from Panning et al. (2018). We find that under most scenarios, group velocity dispersion measurements between periods of 25–250 s can constrain Europa's ice shell thickness to within several km uncertainty, although the method becomes increasingly inaccurate for thicker ice shells and at large epicentral distances. Our results, which suggest that surface waves from naturally occurring ice fracturing events on Europa can be used to help determine ice shell thickness, may help set instrument requirements for spaceflight capable seismometers aimed at exploring icy ocean worlds.
KW - Europa
KW - Ice shell thickness
KW - Icy ocean worlds
KW - Seismology
KW - Subsurface ocean
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U2 - 10.1016/j.icarus.2021.114617
DO - 10.1016/j.icarus.2021.114617
M3 - Article
AN - SCOPUS:85110702979
SN - 0019-1035
VL - 369
JO - Icarus
JF - Icarus
M1 - 114617
ER -