GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 2.2 329 Fig. 2 shows the results obtained at BA06 station, where the effect caused by the superficial waves trapped in recent deposits is greater than in the surrounding areas due to its position inside the basin. Results were compared with a 2D geologic structure model of the Quaternary sedimentary infill of the basin of Chiarini et al. (2014), showing a good consistency with the ground motion site response both in time and frequency domain; in fact, all the analysis allowed to estimate the deposits thicknesses inside the basin using the resonance frequency: as an example, assuming a range of velocity values of 100 and 300 m/s for the deposits, it was estimated a value of thickness between 36 and 107 m at the BA06 station, where the measured resonance frequency is 0.7 Hz. Moreover, the values of resonance frequencies decrease from MN03 (the edge of the basin) to BA06 (in the central part of the basin) stations, while amplitude values increase. An opposite trend is observed from BA06 to BA01 stations, where thickness of the quaternary deposits gradually decreases (see Fig. 1 for stations position). The result is consistent with the study of Chiarini et al. (2014) that describes how geological data (deriving from stratigraphic analysis in 3 boreholes inside the basin and from the superficial stratigraphic limits trends) and geophysical data (gravimetric anomalies) was integrated to model the topography of the quaternary infilling. Statistical analysis. Afirst approach to statistical analysis was conducted in order to identify correlated variables and hidden pattern in our dataset using Principal Component Analysis (PCA). This multivariate statistical technique is used to analyze interrelationships among a large number of variables and consists in finding the directions (or principal components) along which the variation in the data is maximal. The preliminary set of data is obtained from the signal recorded by the 24 seismic stations installed by EMERSITO, and consist of: - resonance frequency and related amplitude for H/V spectral ratio; - resonance frequency and related amplitude for SSR spectral ratio; - resonance frequency and related amplitude of seismic noise; - bedrock depth inferred from QGis database. Preliminary results show that the first 3 components explain 82% of the total variance and that the variable ensemble can be well represented by 3 of 7 considered parameters, i.e. the couple f o , A o (computed either from noise or earthquakes) and bedrock’s depth. Conclusions. This study is a first attempt to evaluate the most important site effect indicators and their correlation and to extrapolate information in new sites with similar geological features. Future development will consist of applying other statistical techniques such as Factor Analysis and Canonical Correlation to find correlations between different parameters and develop predictive models of site response, for both research purposes and future geognostic applications, also in other geological contexts, such as Argostoli area (Greece), the Po Plain (Emilia Romagna region, Italy), Amatrice (Lazio region, Italy), Ischia island (Italy). References Centamore E., Bigi S., Berti D., Morelli C., Micarelli A.; 1992: Carta geologica dei bacini della Laga e del Cellino e dei rilievi carbonatici circostanti (Gran Sasso, Foglio 349) . Scala 1:100.000. S.E.L.C.A., Firenze. Chiarini E., La Posta E., Cifelli F., D’Ambrogi C., Eulilli V., Ferri F., Marino M., Mattei M., Puzzilli L.M.; 2014: A multidisciplinary approach to the study of the Montereale Basin (Central Apennines, Italy) . Rend. Fis. Acc. Lincei, 25 (Suppl 2), S177-S188. http://doi.org/10.1007/s12210-014-0311-3. Cultrera, G., De Rubeis, V., Theodoulidis, N., Cadet H., Bard P.; 2014: Statistical correlation of earthquake and ambient noise spectral ratios . Bulletin of Earthquake Engineering. Volume 12, Issue 4, pp 1493–1514. http://doi. org/10.1007/s10518-013-9576-7 Cultrera G., D’Alema E., Amoroso S., Angioni B., Bordoni P., Cantore L., Cara F., Caserta A., Cogliano R., D’Amico M., Di Giulio G., Di Naccio D., Famiani D., Felicetta C., Fodarella A., Lovati S., Luzi L., Massa M., Mercuri A., Milana G., Pacor F., Pischiutta M., Pucillo S., Puglia R., Riccio G., Tarabusi G., Vassallo M., Mascandola