GNGTS 2017 - 36° Convegno Nazionale

346 GNGTS 2017 S essione 2.2 conditions of each rock block were analyzed by a conventional pseudostatic approach for both planar sliding and wedge sliding mechanisms. The yielding acceleration coefficients (a y ) were computed for each instability (First-Second generation, earth-rock slope) and they were considered as thresholds for calculating the cumulative co-seismic displacements following the rigid sliding block approach by Newmark (1965). Safety factor values were also computed, in case that the pseudostatic coefficient (ah) was lower than the computed a y . By the Newmark’s method it was possible to calculate the cumulative co-seismic permanent displacement of a rigid mass forced by natural time-histories selected from strong-motion databases. The selection criteria were defined according to seismic source characteristics (focal mechanism, magnitude, hypocentral depth), recording-site conditions (free-field installation, Eurocode 8 ground type) and ground-motion parameters (PGA, energy content and target response spectra shape similarity) for a given level of seismic hazard in selected return periods. The earthquake-induced landslide occurrence was expressed in terms of the exceedance probability of the critical displacement (P[DD c ǀ a ( t ),a y ]) responsible of the slope collapse, herein assumed to be 10 cm for earth slides and 5 cm for rockslides (Romeo, 2000). The final comprehensive result of this study consists in a synthetic mapping of possible earthquake-induced scenarios for the Accumoli Municipality. These outputs represent a crucial base-map for zoning unstable areas due to landslide phenomena, i.e. distinguishing attention zone (ZA) from susceptible ones (ZS), according to the guidelines by the Department of National Civil Protection annexed to ICMS 2008 for seismic microzonation studies. Acknowledgements The authors thanks G. De Martino, B. Di Stefano, F. D’Alessandro and C. Missori for their contribution to field activities. These activities were carried on in the framework of the Agreement from Earth Science Department, ENEA and CNR-IGAG (Centro di Microzonazione Sismica) for MS3 studies in the Latium Region (scientific responsible: Salvatore Martino). References Bishop, A.W. 1955. The use of the slip circle in the stability analysis of slope. Geotechnique 5(1): 7-17. Harp, E.L. and Jibson R.W. 1996. Landslides triggered by the 1994 Northridge, California, earthquake. Bulletin of the Seismological Society of America 86: S319-S332. ISRM 1978 “Suggested methods for the quantitative description of discontinuities in rock masses” . International journal of Rock Mechanics and mining sciences & geomechanic. Abstracts 15, 319-368. Janbu, N. 1973. Slope stability computations ., R. C. Hirschfeld and S. J. Poulos (eds), Embankment dam engineering. Casagrande volume, Jhon Wiley and Sons, NY, 47-86 Newmark, N.M. 1965. Effects of earthquakes on dams and embankments, Geotecnique 15: 139-159. Romeo R.W. 2000. Seismically induced landslide displacements: A predictive model. Eng. Geol. 58 (3–4): 337–351.