GNGTS 2013 - Atti del 32° Convegno Nazionale

pulse. In this respect, the solution was approximated with a frequency range of about 0.4-6.2 Hz for “DET1” and 0.4-17 Hz for the richer pulse. Thus, the richer pulse has a larger interval (in linear approximation) where it is possible to validate the geological-geotechnical model by means of comparison with experimental data. Moreover, the 2D mesh size was adapted to the velocity model (mesh adaptivity procedure) in order to reduce the computational cost. The minimum element size was assumed equal to 1/6 of the ratio between the lowest value of V S in the model and the frequency of 10 Hz, chosen as “compromise” frequency between the computational cost and the engineering interest. Consequently the frequency interval, analysed by the richer pulse for 2D modeling, was reduced to 0.4-10 Hz. The resulting bi-dimensional model considered a geotechnical cross section of 3.7 km of width (Fig. 1), with 98139 triangular elements and 49960 nodes. Fig. 2 showed the transfer function computed by considering 1D (red curve) and 2D (black curve) linear models with the richer pulse, as seismic input. Both the numerical analyses detected about 0.7 Hz, as the first fundamental frequency, that is in good agreement with the fundamental frequency of the Standard Spectral Ratio (SSR) at AQ11 station (green curve), a temporary station installed after the April 6, 2009 within the microzonation activities, that recorded earthquakes from 28 May 2009 to 2 July 2009 (MS–AQ Working Group, 2010; Milana et al. , 2011). SSR is evaluated using station AQ12 (Poggio di Roio) as reference site. QUAD4M code showed a slight lower-amplification value at about 0.7 Hz compared to SSR transfer function, while 1D modeling underestimates strongly the amplitude value. The 2D transfer function presented a secondary natural frequency at about 5 Hz and a third one at about 9 Hz, while SSR provides a unique secondary peak centred around 4 Hz. Fig. 3 illustrated the 2D linear and linear-equivalent results, in terms of spectral acceleration, by using “DET1” as input motion. In addition, Fig. 3 showed the 1D elastic response spectrum, obtained by multiplying the spectral acceleration, computed by EERA, with the topographic amplification factor S T , assumed equal to 1.2 (NTC, 2008; CEN, 2003). Conclusions. The huge amount of geological, geotechnical and geophysical data provided by numerous studies in L’Aquila downtown, allowed to rebuild a preliminary subsoil model for the 1D and 2D seismic response analyses of Santa Maria di Collemaggio Basilica. Thanks to the availability of strong motion data close to the Basilica, the site was suitable for an accurate seismic modeling. In fact: the consistent data set available for the sequence of 2009 earthquake supplied the rare opportunity to compare numerical and experimental data. Even thought amplification values are not exactly reproduced, QUAD4M results approximated satisfactorily the experimental ones. 2D analysis was able to reproduce, better than 1D code, the SSR at AQ11 station by considering the whole frequency range (0.4-10 Hz). In this respect, the proposed geotechnical model appeared to be reliable, confirming the presence of 2D effects in L’Aquila downtown. Moreover, these results, although preliminary, suggested the same conclusions stated by Bordoni et al. (2011): the major amplification effects are in the frequency range of 0.5-1.5 Hz. Further numerical simulations will be supplied once all the investigations, supported by Eni, will be available in order to provide a more accurate subsoil model and consequently a more refined elastic response spectrum for all the range of period of engineering interest at Santa Maria di Collemaggio Basilica. References AA.VV .; 2013: Caratterizzazione geologica, geofisica e geotecnica del sito della basilica di Collemaggio . Report Consorzio Sperimentazione Edilizia. University of L’Aquila. <ing.univaq.it/webdisat/cse/cse.html> (In Italian). Amoroso S., Totani F., Totani G., Monaco P.; 2014: Local seismic response in the Southern part of the historic centre of L’Aquila . IAEG XII CONGRESS - TORINO, SEPTEMBER 15-19, 2014 (abstract submitted). Amoroso S., Del Monaco F., Di Eusebio F., Monaco P., Taddei B., Tallini M., Totani F., Totani G.; 2010: Campagna di indagini geologiche, geotecniche e geofisiche per lo studio della risposta sismica locale della città dell’Aquila: 177 GNGTS 2013 S essione 2.2