GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 2.1 - POSTER GNGTS 2023 Method 2D numerical analyses have been performed through an Equivalent Linear approach (EQL) in the time domain solution of seismic shear wave propagation SH. We used LSR2D code (Stacec, 2019). It implements the finite element method FEM that allows calculating stresses and deformations, under total stress conditions, induced by the 2D propagation of horizontal shear waves SH and compressional waves P through soils and rock formations from a horizontal non-rigid rocky bedrock up to the surface. Equivalent Linear analyses are linear analyses that simulate the non-linear and non-elastic behaviour of soils under seismic solicitations. By this method the soil stiffness (G) and damping (D) characteristics are adjusted until they are compatible with the level of the shear strain ( γ ) induced in the soil (Kramer, 1996). Its decreasing curve is measured from lab tests known as cyclic degradation curve. Accordingly, to take into account the damping effects of the cyclic degradation, the damping curve D( γ ) is used to update the damping values to the shear strain level. The whole domain has been divided into triangular elements whose maximum side dimension depends on the cut-off frequency, that is the maximum propagated frequency f max . Commonly, for far-field sites, f max = 15 Hz is assigned. Then, the following rule has been adopted for the maximum element side dimension, to avoid the aliasing phenomenon in the numerical simulation: ℎ = 6÷8∙ (1) The input motion is applied at the bottom of the model domain, and results have been reported in terms of acceleration spectral responses. Finally, lateral boundary conditions have been adopted to simulate the absorption of the wave associated energy by the half-space. The input motion used in 2D numerical analyses is referred to four recorded horizontal components (EW, NS) of the two main shocks recorded at the seismic station named Panchimalco (PA) belonging to the accelerometric network of the University of Central America (UCA). These acceleration time histories have been retrieved from the database COSMOS (https://www.strongmotioncenter.org/vdc ). Seismo-tectonic and geological features of El Salvador El Salvador country is located in the Central American Volcanic Arc (CAVA) that extends from Guatemala to Costa Rica along the active Pacific margin (Fig. 1), where the Cocos plate subducts beneath the Caribbean plate in the Middle American Trench (Crosta et al., 2005; Martínez et al., 2021). The high number of earthquakes in El Salvador region are due to a very high seismic activity associated with two active tectonic systems: (1) the Middle America Trench subduction zone, generating large magnitude earthquakes (Mw > 7); (2) the upper crustal volcanic arc deformation zone, generating moderate to large magnitude earthquakes (Mw ≤ 7). The 13 January 2001 earthquake had a subduction zone generation. The second source of seismicity is characterized by upper crustal earthquakes that are prevalently of tectonic origin and connected to a right-lateral shear zone that is related to the oblique component of the Cocos-Caribbean collision (the February