In this work, the researchers have determined that the small displacement produced by these faults may be due to earthquakes of moderate magnitude caused by them, or to movements caused by first-rate earthquakes generated by other fults of the same system. “Both assumptions –the risponsibles for the research work maintain—are possible as the orientation and nature of the faults of the Alhambra coincides with the regional guideline of major seismic activity in the depression of Granada.
Nevertheless, the seismic risk connected to such faults is moderated, as there is historic damage, written up in different documents, in the recinto of the place of the Alhambra. In this sense, it must be taken into account that the Alhambra, placed on a rocky formation scarcely cemented, “would lessen the local impact of the amplification of the seismic waves with regard to that of soils placed in the centre of the depression of Granada. And, finally, we must not ignore the effect of such faults as mechanic discontinuities that may reduce the stability of the rocky massif causing damage in the constructions placed on it”.
According to Jose Miguel Azañón, of the Andalusian Institute of Earth Sciences and the Department of Geodynamics of the University of Granada, “in the northern hillside of the hill of the Alhambra from the Tajo (cleft) de San Pedro until the Avellano Fountain a good number of normal faults can be surveyed, and in all cases the striations are faced according to the line of maximum slope of the fault plane, for which no side fault can be attributed to these faults. Such faults are comprised between some centimetres and about ten metres”.
According to researchers, “in the Tajo de San Pedro there is a fault of this family of 3.5 metres and parallel to the western side of the Tajo.”
The activity of these faults is, always according to the authors of the study, later than the deposit of the Alhambra Formation, this is, later than lower Pleistocene, if we take the younger rank of ages proposed. In any case, it is reasonable to attribute to these faults Quaternary or even current activity, as they do not appear fossilized by any deposit. Its functioning may have been coseismic, so that faults would accumulate important displacements as a consequence of earthquakes repeated throughout time. “In our opinion –they say—the most important faults of this system, apart from that of the Tajo de San Pedro, would be placed on the topographic steps observed all over the edge of the Depression of Granada”.
Further information: Prof. José M. Azañón
Dpt. Geodynamics- Andalusian Inst. of Earth Sciences
Phone number: 958 249505- 625641014
Fax: 958 248527-958 243384
E-mail: jazanon@ugr.es
