A site amplification factor map of the Iberian Peninsula and the Balearic Islands

Abstract

Considering the lack of site effect cartography in the Iberian Peninsula region to be related to the strong motion data, we present a site amplification factor map covering the Iberian Peninsula and the Balearic Islands. Steps leading to produce the map have included the classification of geological units from the 1:1,000,000 scale Geological Map of Spain into six site classes characterized on a seismic response basis, and the calculation, for every site class, of both short-period and mid-period amplification factors. In order to test the validity and applicability of the map, we have calculated the synthetic seismic intensity in the particular localities where several past earthquakes were felt, supposing a point source approximation. The synthetic intensities have been obtained with and without site amplification factors, resulting in two types of synthetic isoseismals maps that have been compared with the corresponding observed isoseismals. As the amplification factors obtained are only applicable to the linear domain, the synthetic intensities greater than VII are only illustrative. A main conclusion has been drawn about the fact that synthetic isoseismals with site amplification factor approach to the related observed isoseismals in a higher degree than synthetic isoseismals without site amplification factor. In addition, the resemblances between the synthetic isoseismals produced with site amplification factors and the corresponding observed isoseismals have been found to be more evident at shorter epicentral distances, provided that intensities are lower than VIII, and therefore, we remain in the linear domain.