Relations between normal-fault geometry, tilting and vertical motions in extensional terrains: an example from the southern Gulf of Suez

Abstract

Earthquakes and data from subsurface oil exploration suggest that large active normal faults in the southern Gulf of Suez are approximately planar, with dips of 30–40°, from the surface to around 10 km depth. These faults, and the blocks they bound, appear to rotate about a horizontal axis as they move, causing tilting. This tilting is seen both in young vertical movements of the coastline, such as raised beaches and marshlands, and in the distribution of Middle Miocene marine rocks, which are uplifted to elevations of 400–500 m in footwalls of faults and found at depths of around 3500 m in the adjacent grabens. The absolute amplitude of the observed vertical motions can be approximately modelled by planar rotating normal faults that impose a saw-tooth topography on a regional subsidence caused by crustal and lithospheric thinning. The observations required for this simple model are: the present day fault dip, the amount of tilting and the width of the rotating blocks. The virtues of the model are its simplicity and its compatibility with our knowledge of how large active normal faults move elsewhere on the continents.