GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 2.2 475 instrument parallel to the axis of geological structure, which is not necessarily the geographical north. An oblique orientation may otherwise obscure the directional effect completely. This experimental work suggests also a few strengths and weaknesses of the H/V technique: - the possibility to detect 2D effects experimentally with the popular H/V method has important consequences on the evaluation of the seismic site response because 1) it allows the direct measurement of the 2D resonance frequency and 2) it allows to understand when the 1D assumption does not hold and a 2D modelling is needed; - even though a correlation between the 2D resonance and the maximum depth of the valley still exists, the use of the simple resonance equation does not provide correct results in terms of thickness of the resonating layer. Additional studies are required to understand how to link the 2D effects observed in the H/V curves to the laterally changing stratigraphy. Acknowledgements. This study was partly funded by the Geological Survey of the Autonomous Province of Bolzano. References Bard P.Y.; 1998: Microtremor measurements: a tool for site effect estimation? . Proceeding of the Second International Symposium on the Effects of Surface Geology on Seismic Motion , Yokohama, Japan, Vol. 3, pp. 1251–1279. Bard P.Y. and Bouchon M.; 1985: The two-dimensional resonance of sediment-filled valleys . Bull. seism. Soc. Am. , 75, 519–541. Bargossi G.M., Bove G., Cucato M., Gregnanin A., Morelli C., Moretti A., Poli S., Zanchetta S. and Zanchi A.; 2010: Geological Map of Italy at the scale 1:50.000, Sheet 013 “Merano ”. ISPRA – Servizio Geologico d’Italia – Provincia autonoma di Bolzano Castellaro S.; 2016: The complementarity of H/V and dispersion curves . Geophysics,  81, T323-T338. Chávez-García F.J., Raptakis D., Makra K. and Pitilakis K.; 2000: Site effects at Euroseistest-II. Results from 2D numerical modelling and com- parison with observations . Soil Dyn. Earthq. Eng. , 19 (1), 23–39. Fah D., Kind F. and Giardini D.; 2001: A theoretical investigation of average H/V ratios . Geophys. J. Int., 145 , 535–549, doi: 10 .1046/j.0956-540x.2001.01406.x. Haghshenas E., Bard P.Y. and Theodulilis N.; 2008: Empirical evaluation of microtremor H/V spectral ratio. Bull. Earthq. Eng., 6 , 75–108, doi: 10.1007/s10518-007-9058-x. Ibs-von Seht M. and Wohlenberg J.; 1999: Microtremor measurements used to map thickness of soft sediments . Bull. Seism. Soc. Am ., 89, 250–259. Molnar S., Cassidy J.F., Castellaro S., Cornou C., Crow H., Hunter J.A., Matsushima S., Sánchez-Sesma F.J., Yong A.; 2018: Application of Microtremor Horizontal-to-Vertical Spectral Ratio (MHVSR) Analysis for Site Characterization: State of the Art . Surveys in geophysics, 39 , pp. 613 – 631. Pöyry; 2017: Deep seismic profile commissioned by the Autonomous Province of Bozen/Bolzano (in German). Technical report. Sgattoni G., Lattanzi G. and Castellaro S.; 2019: 2D resonance detected with H/V measurements. Bull. Seism. Soc. Am , submitted. A SCENARIO-BASED APPROACH TO GENERATE EMPIRICAL SHAKING MAPS IN CENTRAL ITALY FROM NON-ERGODIC GROUND MOTION MODELS S. Sgobba, G. Lanzano, F. Pacor, C. Felicetta Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Milano, Italy Generation of seismic shaking maps as a tool to support decision making at a given site is a key-topic for civil protection planning and engineering purposes. Currently, shaking fields are based on Ground-Motion Models (GMMs), which estimate the intensity measures as a function of several parameters dependent on the reference earthquake scenario (magnitude, distance, soil category, etc.). However, GMMs are usually provided under the assumption of