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Tidally Driven Frictional Heating and the Seismogenic Zone on Enceladus' Tiger Stripes
  • Maheenuz Zaman,
  • Christine Mccarthy,
  • Heather Savage
Maheenuz Zaman
Cornell University

Corresponding Author:[email protected]

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Christine Mccarthy
Lamont-Doherty Earth Observatory, Columbia University
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Heather Savage
Lamont-Doherty Earth Observatory, Columbia University
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Frictional strength of polycrystalline ice and ice-ammonia mixtures have been measured in the laboratory in order to constrain fault behavior on the south polar region of Enceladus. These faults, known as the tiger stripes, are associated with anomalous temperature gradients and active jets, which have been linked to tidally induced stresses on the faults. The temperature dependence of fault stability is used to map a seismogenic zone within the brittle layer of Enceladus’ icy shell which is estimated as the upper 4 km. The results from our experimental study and models of frictional heating are used to infer fault strength and heat generation within the brittle layer. The friction experiments were conducted using polycrystalline ice and ice-ammonia mixtures in a custom servo-hydraulic biaxial deformation apparatus with a liquid nitrogen-cooled cryostat at icy satellite conditions. The frictional response was measured in steady-state as well as at dynamic conditions, as a function of frequency, amplitude, normal stress, and temperature. For the modelling, a simple 1-D numerical frictional heating model was constructed showing the change in temperature on a fault during sliding. The estimations were based on the solution for heat diffusion through a fault of finite thickness, where temperatures were calculated for different time/space combinations as functions of time during/after slip and inside/outside the slipping zone. Using estimated fault depth and slip distance from previous studies, as well as our experimentally determined friction coefficient, frictional heating with depth was determined with varying values for fault width and slip velocity. Frictional heating models of pure polycrystalline ice will also be compared to that of ice-ammonia partial melt in order to constrain the depth of partial melt within the icy shell, characterizing a possible oxidant transport mechanism into the subsurface ocean. Although we consider sliding on Enceladus, results in this study are additionally applicable to Europa, where instead sulfuric acid may provide the deep eutectic second phase. The identification of the source of seismicity in a tidally loaded fault system could benefit interpretation of seismic observations in future missions to icy satellites.