GNGTS 2013 - Atti del 32° Convegno Nazionale

formation more suitable for hosting the rock reference site and to choose the remaining stations on the base of the different geological characteristics of the sites. The distances between the reference site and the other recording sites were ranging from few tenths of meters up to about three kilometres. This allowed investigating the variation of seismic ground motion at a very local scale, in particular in the historical city centre. The obtained results confirm the presence of important amplification factors in an area where surface geology clearly suggested this possibility. On the other hand our results also showed a strong variability in the seismic response in an area where MS1 was not able to describe some important lateral and vertical variation in the characteristics of the outcropping unit. The recent MS1 practice only very rarely takes into account for earthquake seismic data due to the objective difficulties often found in recovering such a kind of data. Nevertheless we think that MS1 and earthquake data can be used together to improve our knowledge of seismic response. This is particularly true if a seismic sequence of small to moderate magnitude events hits a particular region where MS1 is already available. In fact in these cases it is possible to collect a big number of data in a very short time. In addition to that, MS1 results can help seismologist to select in a more conscious way, the recording sites using the MOPS map as a base for this choice. On the other hands seismic data collected during a seismic sequence can help to better define either the fundamental resonance, also found in the MOPS, the amplification function, that is not provided in MS1, and the presence of differential seismic behaviour and response that can occur in the same MOPS unit. This is particularly true for those geological formations that can present a strong lateral variability that cannot be detected by MS1 due to the lack of in situ geotechnical and geophysical information. References Angelucci A.; 1970: Formazione di Santopadre, Studi illustrativi della Carta Geologica d’Italia: Formazioni geologiche, 4, 149-155, Roma. Bordoni P., Di Giulio G., Haines A.J., Cara F., Milana G., Rovelli A.; 2010: Issues in choosing the references to use for spectral ratios from observations and modeling at Cavola landslide in Northern Italy. Bull. Seism. Soc. Am., 100, 1578–1613 Bocherdt R.D.; 1970: Effects of local geology on ground motion near San Francisco Bay. Bull. Seism. Soc. Am., 60, 29–61 Carrara C., Giraudi C.; 1995: La formazione Plio-Pleistocenica di Santopadre (Lazio, Itala Centrale). Il Quaternario Italian Journal of Quaternary Sciences, 8(2), 1995, 535-552 Esu F., D’Elia B.; 1967: L’influenza della natura dei terreni sugli effetti del terremoto del 13 gennaio 1915 nei centri abitati del Lazio meridionale, R.I.G., 4bis, 1967, 299-311 Gruppo di lavoro MS; 2008: Indirizzi e criteri per la microzonazione sismica. Conferenza delle Regioni e Provincie autonome - Dipartimento della Protezione Civile, Roma, 3 vol. e Cd-rom Konno K., Ohmachi T.; 1998: Ground-motion characteristics estimated from spectral ratio between horizontal and vertical components of microtremor. Bull. Seism. Soc. Am., 88, 228–241 Locati M., Camassi R., Stucchi M. (eds.); 2011: DBMI11, the 2011 version of the Italian Macroseismic Database. Milano, Bologna, (http://emidius.mi.ingv.it/DBMI11 ) Nakamura Y.; 1989: A method for dynamic characteristics estimation of subsurface using microtremor on the ground surface. QR RTRI 30, 25–33 NTC2008, Nuove norme tecniche per le costruzioni, D.M. 14 Gennaio 2008 SESAME; 2004: Guidelines for the implementation of theH/Vspectral ratio technique on ambient vibrationsmeasurements, processing and interpretations. SESAME European research project EVG1-CT-2000-00026, deliverable D23.12 (http://sesame-fp5.obs.ujfgrenoble.fr) Steidl J.H., Tumarkin A.G., Archuleta R.J.; 1996: What is a reference site?. Bull. Seism. Soc. Am., 86, 1733–1748 395 GNGTS 2013 S essione 2.3