Las fallas del recinto de la Alhambra

Abstract

The Alhambra is built on a conglomeratic formation, known as the Alhambra Formation, whose age is Pliocene to Lower Pleistocene and has a visible thickness of 200 metres. The western part of the San Pedro escarpment corresponds to a fault-scarp with some retreat; the fault-plane outcrops in the innermost part of the escarpment, showing normal displacement and NW-SE strike with NE steep dip. This fault is the most important one of a set that outcrops along the northern hillslope of the Alhambra. Several topographic steps with NW-SE orientation are interpreted as retreated fault-scarps. In some cases, the activity of these faults seems to be very recent and maybe related to earthquakes. The seismic risk associated with these faults (and maybe some not-outcropping ones) can be taken to be moderate, as some historical damages have been reported concerning the Alhambra walls and the fence. In this respect, the Alhambra fence has numerous cracks geometrically related to fault planes outcropping in the Alhambra Formation, i.e. faults and cracks are continuous and have similar strike and dip. We hypothesize that these cracks are due to small displacements along the faults, occurred during recent earthquakes in the region. These faults constitute mechanical discontinuities, which represent a supplementary risk, because they contribute to reduce the stability of the entire rock massif