GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 2.1 - POSTER GNGTS 2023 13, 2001, earthquake is an example of this). The city of San Salvador is the capital of the country, also known as MASS (Metropolitan Area of San Salvador), and it is located within the Central Graben straddling two active volcanoes: San Salvador to the northwest and Ilopango to the southeast. Figure 1. Geographic and tectonic setting of El Salvador region. The geological setting of the country is the product of intense geodynamic and tectonic activity: the entire urban territory, from a geological point of view, includes the products of basalt/andesite stratovolcanoes and the interstratific silica tephra/ignimbrites of Coatepeque and Ilopango Calderas (Chàvez et al., 2012). Dominating the entire area are the volcanic deposits of the Tierra Blanca, a dalacitic pumice ash composed of acidic pyroclastic and epiclastic deposits. These deposits can be classified as a sandy silt or silty sand (Bommer et al., 2001) and subdivided into four main units which, from the oldest to the most recent, are named respectively TB4, TB3, TB2 (Tobas superiores) and TBJ (Tierra Blanca Joven) (Rolo et al., 2004). The latter unit represents the most widely found soil resulting from the last explosive eruption that covered the entire current urban territory with different thicknesses (Hernàndez, 2008). The depositional variability in the TBJ deposits, in terms of thickness, creates slope instability conditions and seismic amplification phenomena. Subsoil model and 2D analyses results of local seismic response The sites examined for the reconstruction of the two-dimensional subsurface model located within the MASS are: 1. IGN - "Instituto Geografico Nacional" (13.7127, -89.1698), 2. CIG - "Centro de Investigaciones Geotecnicas" (13.6987, -89.1733), 3. HDN - "Hogar del Niño" (13.6877, -89.1881), and 4. OBS - "Observatorium" (13.6810, -89.1980).