Migration of activity within normal fault systems: examples from the Quaternary of mainland Greece

We examine five areas of mainland Greece where active extension occurs on sub-parallel systems of normal faults, and where geomorphological and stratigraphic evidence indicates that the faulting has migrated basinwards into the original hanging walls, in several cases within the late Quaternary. By comparing fault slip rates estimated from geomorphological data with current extension rates known from geodetic measurements, it appears that the newest faults can account for effectively all the present-day motions. Fault migration of this sort is easy to recognize in young systems close to sea level, because vertical movements of footwalls and hanging walls are obvious and reveal which faults are currently most active, but is less easy to confirm away from reliable reference levels or in older terrains with poorer time resolution. It is probably more common than is appreciated, and has a profound effect on syn-rift sedimentation and erosion patterns. Fault migration is probably an inevitable consequence of the interplay between stresses generated by the fault-related topography and the ultimate strength of major faults. It is likely to be further encouraged in places where lower crustal flow or rotations about a vertical axis are important. However, it is not clear why migration should preferentially occur into the hanging walls, as observed in central Greece.