DISPLACEMENT MAGNITUDE AND DISTRIBUTION ALONG AGENOR LINEA, EUROPA: EFFECT OF ORBITAL ECCENTRICITY

Agenor Linea (AL) is a ~1500 km long, E–W trending, 20–30 km wide zone of geologically young deformation in the southern hemisphere of Europa. Based on predictions of stress orientations and photogeological evidence, AL is primarily a right-lateral strike slip fault. Our previous work has shown that a combination of both diurnal and non-synchronous rotation (NSR) stresses could promote failure along AL. We also have shown that under present day conditions (eccentricity e = 0.0094, nominal eccentricity model), slip does not occur along the entire length of AL, even with additional stresses imparted by the slipped segments. In order to investigate under what conditions AL accumulates displacement, stresses and displacements were calculated for minimum (e = 0.0) and maximum (e = 0.02) eccentricity models.

Tidal stresses are calculated using SatStress, a numerical code that calculates tidal stresses at any point on the surface of a satellite for both diurnal and NSR stresses. We adopt model parameters appropriate for a 20 km thick ice shell underlain by a global subsurface ocean. We assume a coefficient of friction of 0.6, NSR period 1.4x10⁵ yr, and a range of vertical fault depths to 4 km.

Shear failure at AL is assessed based on the Coulomb failure criterion, which balances stresses that promote and resist fault motion. Shear failure occurs where the shear stress exceeds the frictional resistance of the fault. Coseismic displacements are calculated for fault segments that meet the conditions for shear failure, assuming full stress drop.

Failure occurs at 1–3 km depth for all three eccentricity models; no displacement is calculated below 3 km. Displacement magnitudes are similar for all models, with maximum right-lateral displacements ≈45 m. For all models, failure is concentrated on the west end of AL at 1 km depth and shifts eastward with increasing depth. In all models, ~75% of fault segments fail at 2 km depth. However, portions of AL show no slip from the modeled tidal stresses alone.

Failure of a portion of a fault may trigger failure on adjacent portions; this is known as stress triggering. Our results show that under particular circumstances, stress triggering can occur, with more failure occurring at higher eccentricity. Large portions of AL remain un-slipped. Future work will investigate the role of NSR period on fault failure.