GNGTS 2013 - Atti del 32° Convegno Nazionale

by considering the contribution of the infill walls that modern codes do not consider adequately. • Significant differences were observed between the fundamental periods obtained for RC and MA buildings, the former being usually higher than the latter. This behaviour appear related, as suggested by the results of damping estimates, to the different stiffness of the structures and to the presence of connected adjacent buildings, especially in the historical centre of the town. • The ground motion parameters, estimated using the 1990 earthquake source, highlighted that the areas where amplification effects take place, match up to sites where sedimentary terrains outcrop. • Contour maps of PGA values seem to be affected by the site-to-source distance whereas, the PGV appears a reliable indicator of the role played by the lithology confirming e good correlation with the macroseismic intensity data. • H/V spectral ratios performed on the main outcropping lithotypes, show a good agreement with results coming from the analysis of the scenario earthquake. These outcomes validate indeed the presence of local amplification effects on thick sedimentary terrains, pointing also out some critical behavior in connection with some spots of the limestone formation, especially in Ortigia, and in sites where detritus outcrops. In conclusion, we have observed that major damage occurred during the 1990 earthquake are located in the Ortigia downtown area. This can be considered as the consequence of both the poor quality of some buildings and the local amplifications taking place especially on the sedimentary terrains. It was indeed observed that considering buildings having height of about 20 m, a MA building will oscillate with a period of about 0.2 s whereas, a RC building will oscillate with a period of about 0.4 s. In terms of spectral accelerations, the MA building will be subject to an effect that is about 1.5 times greater than the RC one (PSA ranging between 250-600 cm/s 2 and 150-450 cm/s 2 , for 0.2 s and 0.4 s, respectively). Finally, the used methodologies in our opinion represent the preliminary steps for a fast, practical and inexpensive procedure aiming to determine the regional vulnerability and the mitigation priorities, for large cities like Siracusa that in the past have been affected by destructive earthquakes. References Amato A., Azzara R., Basili A., Chiarabba C., Cocco M., Di Bona M., and Selvaggi G.; 1995: Main shock and aftershocks of the December 13, 1990 Eastern Sicily earthquake . Ann. Geofis. 38(2), 255-266. Argnani A., and Bonazzi C.; 2005: Malta Escarpment fault zone offshore eastern Sicily: Pliocene-Quaternary tectonic evolution based on new multichannel seismic data. Tectonics 24, TC4009, 1-12. Barbano M.S., Rigano R., Cosentino M., and Lombardo G.; 2001: Seismic history and hazard in some localities of south- eastern Sicily . Boll. Geofis. Teor. Appl. 42(1-2), 107-120. Basili R., Valensise G., Vannoli P., Burrato P., Fracassi U., Mariano S., Tiberti M.M., and Boschi E.; 2008: The Database of Individual Seismogenic Sources (DISS), version 3: summarizing 20 years of research on Italy’s earthquake geology . Tectonophysics 453(1), 20-43. Beresnev I.A., and Atkinson G.M.; 2002: Source parameters of earthquakes in eastern and western North America based on finite-fault modeling . Bull. Seismol. Soc. Am. 92, 695-710. Bianca M., Monaco C., Tortorici L., and Cernobori L.; 1999: Quaternary normal faulting in southeastern Sicily (Italy): a seismic source for the 1693 large earthquake. Geophys. J. Int. 139, 370-304. Boore D.M.; 2009: Comparing stochastic point-source and finite-source ground-motion simulations: SMSIM and EXSIM. Bull. Seism. Soc. Am. 99, 3202-3216. Crowley H., and Pinho R.; 2006: Simplified equations for estimating the period of vibration of existing buildings . Proceedings of 1st European Conference on Earthquake Engineering and Seismology, Geneva, paper no. 1122. Eurocode8; 2003: Design of structures for earthquake resistance. Part1: general rules, seismic actions and rules for buildings , CEN European Committee for standardization, Brussels. Faccioli E. and Pessina V.; 2000: The Catania project: earthquake damage scenarios for a high-risk area in the Mediterranean . CNR-GNDT, Roma, pp. 1-225. Finetti I.; 1982: Structure, stratigraphy and evolution of the Mediterranean Sea . Boll. Geo. Teor. Appl. 15, 263-341. Goel R.K., and Chopra A.K.; 1997: Period formulas for moment resisting frame buildings . J. Struct. Eng. ASCE 123(11), 1454–1461. 108 GNGTS 2013 S essione 2.1