GNGTS 2015 - Atti del 34° Convegno Nazionale

Soil classification. The geology of the site has been often used to justify the local shaking increase observed during earthquakes. Many researchers have proposed empirical correlations between surface geology and local seismic severity. The use of surface geology in seismic microzoning is very practical and applicable to many areas. In this work, we have used the geological map of the region (Medina et al ., 1999) to define a soil classification and get an approximate estimation of the local effects. The various stratigraphic units have been classified according to the NERHP (BSSC, 2001) provisions (Tab. 2 and Fig. 2). Tab. 1 - Average velocities (V S ) and depth (h) for main materials in the study region. Soil Density Av. Vs Av. Depth Trendline (kg/m 3 ) (m/s) (m) Silty clay 1.85 179 2.19 V S = 3.2591 · h + 171.86 400 70.00 Clay 1.87 290 3.18 V S = 1.566 · h + 285.02 700 265.00 Sand 1.89 348 4.20 V S = 2.5251 · h + 337.39 600 104.00 Gravel and sand 1.91 443 4.27 V S = 1.5107 · h + 436.55 500 42.00 Conglomerate 1.95 300 3.00 V S = 5.9524 · h + 282.14 800 87.00 Marl clay 1.93 438 5.60 V S = 3.7945 · h + 416.75 800 101.00 Sandstone 1.94 504 8.92 V S = 1.3795 · h + 491.69 700 151.00 Limestone marl 2.04 622 8.06 V S = 1.936 · h + 606.4 800 100.00 Tab. 2 - Soil classification according to the NERHP provisions (BSSC, 2001) for the stratigraphic units in the study area. Stratigraphic units Geological description NERHP Fm Varadero Marine beach deposits. E Fm Río Macío Deposits of alluvial valleys. E Fm Jaimanitas Biodetrital limestones, carz, very fossiliferous B with shell and corals. Fm Camaroncito Calcarenite with gravel C Fm Río Maya Biohermal limestone, dolomite, clays and intercalation B of polimictict conglomerates. Mb Santiago Calcareous argillite, silty sands wih intercalation D of aleurolite and calcilutites. Mb Tejar Biodetritical limestones, calcareous sands, marls, C calcarenite, conglomerates and polymictict grits. Mb Quintero Polimictict conglomerates. C Gp El Cobre Volcanic and volcanic-sedimentary rocks. B Tuff, tuffites, limestones, lapilli, lavas. GNGTS 2015 S essione 2.2 173