Astypalaea Linea: A large-scale strike-slip fault on Europa

Astypalaea Linea is an 810-km strike-slip fault, located near the south pol e of Europa. In length, it rivals the San Andreas Fault in California, and it is the largest strike-slip fault yet known on Europa. The fault was disc overed using Voyager 2 images, based upon the presence of familiar strike-s lip features including linearity, pull-aparts, and possible braids, and upo n the offset of multiple piercing points. Fault displacement is 42 km, righ t-lateral, in the southern and central parts and probably throughout. Pull- aparts present along the fault trace probably are gaps in the lithosphere b ounded by vertical cracks, and which opened due to fault motion and filled with material from below. Crosscutting relationships suggest the fault to b e of intermediate relative age. The fault may have initiated as a crack due to tension from combined diurna l tides and nonsynchronous rotation, according to the tectonic model of R. Greenberg et al. (1998a, Icarus 135, 64-78). Under the influence of varying diurnal tides, strike-slip offset may have occurred through a process call ed "walking," which depends upon an inelastic lithospheric response to disp lacement. Alternatively, fault displacement may have been driven by current s in the theorized Europan ocean, which may have created simple shear struc tures such as braids. The discovery of Astypalaea Linea extends the geographical range of lateral motion on Europa. Such motion requires the presence of a decoupling zone o f ductile ice or liquid water, a sufficiently rigid lithosphere, and a mech anism to consume surface area. (C) 1999 Academic Press.