GNGTS 2015 - Atti del 34° Convegno Nazionale

constituted by Paleogene rocks, volcanic-sedimentary rocks of the Cobre Group and some bodies of andesite and basalt (Medina et al ., 1999). The study area is crossed by numerous geologically active normal and strike-slip faults (Medina et al ., 1999), these faults cut the basin with different directions but without any documented seismicity. However, they play an important role in characterizing the deep geometry of the basin and, consequently, they condition the local amplification characteristics of the soils. The main seismotectonic structure of southern Cuba is the Oriente Fault, it constitutes a displacement fault that causes the horizontal translation of tectonic blocks. Its geometry and tectonic regime were better defined by Calais and Mercier de L������ ������ ����� ������� ��� é����� ������ ����� ������� ��� pinay (1990, 1991) through the interpretation of marine geophysical data. Moreno et al . (2002) characterized the activity of the local faults and their stress regime. We have developed a 3D geotechnical model of the Santiago de Cuba (Rivera et al ., 2013) on the basis of 61 geological profiles (Fig. 1) calibrated on all the available geological [geological- tectonic map of Santiago de Cuba at the scale 1:25,000 of Medina et al . (1999) and stratigraphic Cuban lexicon of Carrillo et al . (2009)], geophysical (electrical and seismic soundings), and geotechnical (geological and geotechnical boreholes) data. These profiles cross the entire city in a regular grid of 500 m × 500 m and take into account the superficial and deep soil topography, the shear wave velocity (V S ) in each layer, and the physical-mechanical properties of the layers themselves. The geological model has, then, identified the areas where a 1D or 2D modelling is more suitable. The deep geological and geotechnical information come from several geotechnical surveys: 550 soil profiles from geotechnical boreholes, performed by a local engineering and geological research institution (ENIA-Santiago) belonging to the Cuban Ministry of Construction, and 11,120 logs of geological borings from the Geominera East Company (EGMO), collected in a data set by Mendez et al . (2001). The two methods of local geophysical prospecting of refraction seismics and electrical resistivity were performed along 33 seismic profiles. Twelve 10-Hz vertical geophones, disposed equidistantly, were used in the first method, aiming at determining the velocity variations of the longitudinal waves in depth according to the different layers; the ground was energized by a 10-kg hammer on an aluminium plate. Sixteen steel electrodes, disposed equidistantly with respect to the site, were used in the second method, aiming at determining the ������������ �� ������������ �� distribution of the lithological heterogeneities in the ground. These methods have the limitation that only the surficial layers can be characterized. All information about the stratigraphic wells, together with all tectonic and geophysical data, were stored in several databases, with their coordinates, maximum depth, phreatic level, thickness, lithological description, stratigraphic characteristics, and physical-mechanical properties of each layer. The electrical resistivity values derived from the interpretation of the cited profiles were adjusted in accordance with those obtained by �������� ������� ��� ������� ��� ���� ������� Orellana (1982), Das (2001), and Loke (2004). The velocity of the longitudinal waves, obtained by V S =V P ·1.74 (Moreno et al ., 2002), was compared with that obtained by Redpath (1973) and Das (2001), and confronted with the interpretation of the electrical resistivity ������������ ��� �� ��� ���������� ����� ������ �� (tomography) ��� �� ��� ���������� ����� ������ �� and of the geological wells nearby to geophysical profiles. The velocity at the different depths for eachmaterial has been calculated from the geophysical characteristics of the outcropping layers of that material� ���������� ��� ����������� ������ ���� , neglecting the superficial layers with a depth less than 1 m and taking into account its maximum depth. ��� ��� ������ ������� ����� ��� ��� ������ ������� ����� For the deeper layers, where it was not possible to calculate the velocity experimentally, we have taken into account the average values of densities and seismic wave velocities (Sadovskii et al ., 1973). In this way, we have obtained a trendline that allows us to calculate the velocity values in any point of the deep layers (Tab. 1). The density values (Tab. 1) were obtained from the data of the geotechnical boreholes and compared with the available literature (NAVFAC, 1982). 172 GNGTS 2015 S essione 2.2