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The process of tide-driven walking, proposed as a major mechanism for strike–slip displacement on Europa, is modeled using a finite-element numerical simulation of the behavior of viscoelastic material. For material parameters that are plausible for the water ice composing Europa's crust, the simulation confirms earlier analytic results for strike–slip displacement along a crack that penetrates down to the liquid water substrate. The finite element code permits testing other cases as well. Of considerable interest is whether tidal walking can operate if a crack penetrates not to liquid but only as far as warm, relatively viscous ice. In such a case, significant displacement can be driven, but only if the threshold value of the compressive force needed to lock the fault is near the value of the overburden stress at the bottom of the crack. Such special conditions are not needed for displacement if the crack penetrates to the underlying ocean.

[1] Zunil, a 10.1 km rayed crater in Elysium Planitia, Mars, produced more than 7 × 107 secondary craters ≥15 m in diameter. We mapped Zunil's rays from thermal IR THEMIS nighttime images up to 1700 km from the primary crater and mapped bright and dark ejecta craters (candidate secondaries) up to 3600 km range. Ray segments were mapped up to 450 km east of Zunil and up to 1700 km to the west. Both rays and bright ejecta craters are best detected over terrains with moderate thermal inertia, which are abundant west of but not east of Zunil. Nevertheless, our interpretation is that Zunil was created by a moderately oblique impact from the east. Zunil secondaries are abundant over all terrain types except the Medusae Fossae Formation (MFF). Given the likely age of Zunil (