GNGTS 2013 - Atti del 32° Convegno Nazionale

The aim of this work is the definition of a geotechnical model for the Santiago de Cuba basin for the future 2D modelling of the expected ground motion determined by considering a scenario earthquake and the amplification caused by the local soil response. Basic data used. The correct characterization of a site for seismic hazard purposes requests a good knowledge of several topics: geology, tectonics, geotechnics, geophysics, topography, and bathymetry. a. Geology. Geological data are the basic information for the site characterization. We have used the geological-tectonic map of Santiago de Cuba city at the scale 1:25,000 (Medina et al. , 1999), integrated with additional information from the stratigraphic lexicon (Carrillo et al. , 2009) and further available literature related to this topic. The cited geological map of Santiago de Cuba city (modified from Medina et al. , 1999) is reported in Fig. 1: the red lines are the superficial projection of the Quaternary faults and the solid dots are the geotechnical boreholes and geological wells available and used in this study. The Santiago de Cuba basin is characterized by low complexity in lithological variability, some geological formations are widely disseminated in the city broader area. Tab. 1 shows the geological formations and a brief description of these. Tab. 1 - Lithostratigraphic information of the geology formations in the study area. Age Geological formation Geological description Depth (m) Q 4 var = Varadero Marine beach deposits. 5 Q 4 río = Río Macío Deposits of alluvial valleys. 10-20 Q 1 sup js = Jaimanitas Biodetrital limestones, very fossiliferous with shell and corals. 10 N 2 su crt = Camaroncito Calcarenite with gravel. 4 N 2 sup -Q 1 inf rm = Río Maya Coralline limestone, dolomite, clays and intercalation of polimictic conglomerates. 30-80 N 2 inf stg = Santiago Calcareous argillite, silty sands with intercalation of aleurolite and calcilutites. 10 N 2 inf -N 1 sup tj = Tejar Biodetritical limestones, calcareous sands, marls, calcarenite, conglomerates and polymictic grits. 100 N 1 sup - N 1 med qt = Quintero Polimictic conglomerates. 15 P 1 -P 2 med-a ec = El Cobre Volcanic and volcanic-sedimentary rocks. Tuff, tuffites, limestones, lapilli, lavas. 5000-6000 Legenda: Q4- Quaternary; Q 1 inf Lower Pleistocene; Q 1 sup Upper Pleistocene; N 2 inf Lower Pliocene; N 2 sup Upper Pliocene; N 1 sup Upper Miocene; N 1 med Middle Miocene; P 1 Paleocene; P 2 med-a Lower middle Eocene. b. Tectonics. The identification of the active geological faults in the study region was based on those located onshore and proposed as active in the last 20 M.a. (of Miocene to Holocene) by Medina et al. (1999). These faults are not capable to generate a medium/ large earthquake, but play an important role in the local amplification characteristics. Moreover, it is very important to have information on the deep geometry of the faults (e.g., dip, locking depth). c. Geotechnics. In order to obtain a valid description of the variation of the soil properties with depth, we have used the geological and geotechnical information coming from several geotechnical surveys: 550 soil profiles from geotechnical boreholes performed by a local engineering and geological research institution (ENIA-Santiago) belonging 331 GNGTS 2013 S essione 2.2