Slip sliding away: calculating cyclic slip magnitudes on tidally driven faults on europa,

Faults on Europa likely slide back and forth 0.01 – 2 m per orbit in response to diurnal tidal stresses. Slip magnitudes depend strongly on the resolved stress shear magnitude, the coefficient of friction on the fault and the elastic properties of the fault zone. Cyclic slip causes substantial frictional heating, potentially enough to generate a zone of partial melting within 1 km of the surface. The rate of permanent fault slip dramatically increases once a warm, melt-rich layer is established at the base of the fault. Introduction: Several studies have examined shear heating along strike-slip faults on Europa, which could potentially produce melting [1 – 3]. Near-surface melting from shear heating could strongly impact both the habitability and geologic resurfacing of Europa. Melts produced by shear heating could impact the formation of ridges [4,5], supply a water source for recently detected vapor plumes [6] and possibly enable the transport of oxidants from the surface to the subsurface ocean as near-surface melts migrate downward [2,3,7]. Do Europa’s faults slide fast enough to generate melting? Previous investigations have modeled permanent sliding along strike-slip faults (as opposed to cyclic sliding where faults return to the same position each orbit), and found that permanent sliding rates of ~30 m/yr may be necessary to cause melting [1,2]. Previous work has also assumed sliding rates as a boundary condition, without showing how the sliding rate should be controlled by the resolved shear stress acting on the fault. Model: Here we calculate the magnitude of cyclicslip along strike-slip faults on Europa. A MohrCoulomb model is used to predict the depth of frictional failure from diurnal tidal stress of ~100 kPa in magnitude [8]. Sliding is possible at a particular depth z, when the shear stress magnitude exceeds the failure stress τ!, τ > τ! = μ σ! + ρgz . Here τ and σ! are the resolved shear and normal stress on the fault from tidal deformation, ρ is the density of the ice shell, g =1.34 m/s is Europa’s surface gravity and μ is the coefficient of friction of ice on the fault. We test a range of coefficients of friction from μ = 0.1 – 0.7, consistent with experimental findings [9]. Faults experience alternating phases of tension and compression and left and right-lateral shear [10], causing the failure depth to vary over time. Figure 1: a) Schematic for cyclic-slip along faults on Europa. b) Calculations for cyclic-displacement with depth over the tidal cycle, assuming a tidal stress amplitude of 100 kPa, G=0.3 GPa and μ = 0.1. An elastic half space model is used to calculate cyclic displacements between the fault walls, assuming the fault is locked below the maximum frictional failure depth, d!. Shear stresses in excess of the failure stress cause elastic displacements between the fault walls [11].