GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 2.2 385 Finally the seismic bedrock interface has been mapped throughout the basin, showing values in general ranging between 100 m and 300 m of depth, deepening toward the Adriatic Sea, where the velocity gradients are lower and the H/V peak corresponding to the seismic bedrock interface moves at lower frequencies. The seismic bedrock interface appears related to different stratigraphic discontinuities based on the zone. In particular, in the western part of the plain near Pavia and Milano, it seems corresponding to the base of the 2 nd aquifer (Regione Emilia- Romagna, ENI – AGIP, 1998; Regione Lombardia, Eni Divisione Agip, 2002), except for a few stations in the northern sector where it may be related to a deeper surface. In the central and most extended part of the Plain, it could be related to the base of the 1 st aquifer (Regione Emilia-Romagna, ENI – AGIP, 1998; Regione Lombardia, Eni Divisione Agip, 2002), but for those sites in the northernmost sector (near the Garda Lake) and for some in the southernmost sector (near the Apennines) it seems still related to the base of the 2 nd aquifer. For the stations in correspondence of the top of the buried structural highs of S. Colombano, Mirandola and Casaglia (Pieri and Groppi 1981; Martelli and Romani 2013), the seismic bedrock interface could be related to the base of the Quaternary sediments, in correspondence of the contact with Low-Pliocene or Miocene Marls, raised to shallow depth by buried structural highs. East of Ferrara Arc (Pieri and Groppi 1981), the seismic bedrock interface deepens toward the Adriatic Sea and it could be related to a deeper discontinuity inside the 2 nd aquifer. The preliminary map of the Po Plain seismic bedrock, allows for a site effects estimation useful for both scientific and applied purpose. In particular, considering that in the target area the seismic bedrock interface lies well below the depth range (0-30 m) considered in the engineering practice (MASW, refraction, etc.), this study can be a benchmark for local seismic response analyses and new hazard studies at regional scale, when just Near-Surface Geophysics is available. References CEN; 2003: prEN 1998-1- Eurocode 8: design of structures for earthquake resistance. P1: General rules, seismic actions and rules for buildings. Draft 6, Doc CEN/TC250/SC8/N335. Fantoni R., Franciosi R.; 2010: Tectono-sedimentary setting of the Po Plain and Adriatic foreland. Rendiconti Lincei, 21(1), 197-209. FontanaA., Mozzi P., Marchetti M.; 2014: Alluvial fans and megafans along the southern side of the Alps . Sedimentary Geology, 301, 150-171. GeoMol Team; 2015: GeoMol – Assessing subsurface potentials of the Alpine Foreland Basins for sustainable planning and use of natural resources. Project Report, 188 pp. Ibs-von Seht M., Wohlenberg J.; 1999: Microtremor measurements used to map thickness of soft sediments . Bulletin of the Seismological Society of America, 89(1), 250-259. Laurenzano G., Priolo E., Barnaba C., Gallipoli M.R., Klin P., Mucciarelli M., Romanelli M.; 2013: Studio sismologico per la caratterizzazione della risposta sismica di sito ai fini della microzonazione sismica di alcuni comuni della Regione Emilia Romagna. Atti del, 32, 247-252. Laurenzano G., Priolo E., Mucciarelli M., Martelli L., Romanelli M.; 2017: Site response estimation at Mirandola by virtual reference station. Bulletin of Earthquake Engineering, 15(6), 2393-2409. Martelli L., Romani M.; 2013: Microzonazione Sismica e analisi della condizione limite per l’emergenza delle aree epicentrali dei terremoti della pianura emiliana di maggio-giugno 2012, relazione illustrativa. Servizio geologico, sismico e dei suoli Regione Emilia Romagna. Martelli L. (coord.), Bonini M., Calabrese L., Corti G., Ercolessi G., Molinari F. C., Piccardi L., Pondrelli S., Sani F., Severi P.; 2017: Carta sismotettonica della Regione Emilia-Romagna e aree limitrofe, scala 1:250.000 (edizione 2016). Con note illustrative. Regione Emilia-Romagna, SGSS; CNR, IGG sez. FI; Università degli Studi di Firenze, DST; INGV sez. BO. D.R.E.AM . Italia. Mascandola C., Massa M., Barani S., Lovati S., Santulin M.; 2017: Long-Period Amplification in Deep Alluvial Basins and Consequences for Site-Specific Probabilistic Seismic-Hazard Analysis: An Example from the Po Plain (Northern Italy). Bulletin of the Seismological Society of America, 107(2), 770-786. Minarelli L., Amoroso S., Tarabusi G., Stefani M., Pulelli G.; 2016: Down-hole geophysical characterization of middle-upper Quaternary sequences in the Apennine Foredeep, Mirabello, Italy. Annals of Geophysics, 59(5), 0543. Nakamura Y. ; 1989: A method for dynamic characteristics estimation of subsurface using microtremor or the ground surface . Quart. Rep. Rail. Tech. Res. Inst. (RTRI), 30 (1).