GNGTS 2015 - Atti del 34° Convegno Nazionale

The AFs based on the NERHP (BSSC, 2001) soil classification (Fig. 2), show a high amplification (AF from 1.6 to 2.5) where Quaternary sediments and argillites of the Mb. Santiago outcrop. More precisely, the highest amplifications (2.5) are estimated around Santiago de Cuba Bay and along the river valleys, where the most recent Quaternary sediments outcrop. Amplifications between 1.2 and 1.6 are estimated in the Neogene sediments, whereas no amplification is expected around the southern border of the coast, where the limestone of the Fm. Jaimanitas outcrop, and to the north and NW of the bay, where volcanogenic sedimentary rocks of Gp. Cobre outcrop. The AFs based on 1D and 2D modelling (Fig. 3) show larger variability than those in the NEHRP map especially in the poorly compacted Neogene - Quaternary sediments, classified in Fig. 2 as stiff or soft soils. The highest amplifications (AF larger than 1.7) correspond to the thickest sediments. When comparing the map (Fig. 2) with AFs based on the NERHP provisions (BSSC, 2001) with that based on 1D and 2D modelling (Fig. 3), we see that the modelling leads to lower AFs along the western coast of the Santiago de Cuba Bay as well as along the San Juan Basin. Almost no amplification is expected in a few sectors of limited dimensions by modelling, conversely, a low amplification is suggested by the NEHRP soil classification. Moreover, there is a good agreement by modelling and NEHRP AFs where the soil is classified as stiff soil (NEHRP class D), although some spots with high AF (larger than 1.7) appear in the map based on the modelling results. Conclusions. From the geotechnical model (Rivera et al ., 2013), we have obtained 225 stratigraphic models for the whole study area of Santiago de Cuba, taken into account the local geology (tectonic setting and geological description: age, lithological description, stratigraphic characteristics, sediment thickness) and geotechnical information (physical-mechanical properties: density, Poisson coefficient, damping). The static soil properties (shear wave velocity) have been defined from data of geophysical prospections and using the relationship of Moreno et al . (2002). The expected AFs for Santiago de Cuba have been estimated from the NERHP (BSSC, 2001) soil classification (Fig. 2), based on the stratigraphic units present in the study area, and from the 1D and 2D modelling (Fig. 3), taking into account the local soil properties and 6 suitable UHRSs for bedrock. The AFs from modelling have been estimated as the ratio of the output over the input spectrum in the range of periods from 0.1 to 0.5 s. The results show that no amplification is expected along the coast of the Caribbean Sea with the exception of a small portion to the SW, where Quaternary sediments appear. A similar behavior can be seen to the north and west of the bay, where volcanogenic sedimentary rocks outcrop. A small sector located to the east of Fig. 3 – AFs for the Santiago de Cuba broader region computed from 1D and 2D modelling as the ratio of the output over the input UHRS in the range of periods from 0.1 to 0.5 s. GNGTS 2015 S essione 2.2 175