GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 2.2 GNGTS 2023 Local 2D seismic response The central zone of the valley is flat and lies between slopes with gradients of 12°÷15°. As described above, the subsoil is characterised by lateral and vertical variability, both as regards thickness and texture; the substratum, outcropping on the slopes of the valley, deepens up to about 20 m below ground level. In view of these conditions, the seismic hazard estimate was determined using a 2D calculation code. The code used (LSR-2D, Stacec Srl) involves two-dimensional modelling of the seismic lithological sequence by means of finite elements, in the time domain, in terms of total stresses, using the equivalent linear method and with reference to the deformability of the substratum. The lithostratigraphy of the significant subsoil volume was determined on the basis of the geological cross-section whose trace is shown in Figure 1. The geotechnical-seismic model is summarised in Table 1. Table 1: Geotechnical and seismic model adopted for the calculation of surface shaking Depth (m) Lithotype n. Vs (m/sec) Gmax (MPa) Volume weight (KN/mc) Initial attenuation factor (%) Location and type of input earthquake from surface to -1÷-3 m 2 100÷200 18÷75 18÷18.5 - - from -1÷-3 to -7÷-8 m p.c. west zone 4 450 408 19.8 - - from -1÷-3 to -10÷-18 m p.c. central zone 5 250÷320 120÷200 18.8÷19.1 - - from -10÷-18 to -20÷-30 m p.c. central zone 4 360÷450 255÷408 19.3÷19.8 - - from -15÷-18 to -25÷-30 m p.c. central eastern zone 4 530÷570 580÷690 20.3÷20.7 - - from -7÷-9 to -15÷-30 m p.c. - 670÷700 990÷1100 21.5÷21,7 1÷1,2 - below -15÷-30 m - 800 1500 22 0.3 Outcrop Seismic inputs The input signals for the surface shaking simulations are those available on the webgis platform http://egeos-test.eucentre.it/rer/home.html , which consist of a group of 7 real accelerograms, recorded on rock, spectrum-compatible with NTC18 spectra, for TR=475 years.