GNGTS 2016 - Atti del 35° Convegno Nazionale

356 GNGTS 2016 S essione 2.2 A Multiple Hazard Approach to Seismic Amplification Effects and Seismically-Induced Boulder Falls at Casentino City Site (AQ) C.A. Garzonio 1 , M.L. Rainone 2 , G. Vessia 2 , L. Dimichele 2 , G. D’Elia 2 1 Department of Earth Sciences, University of Florence, Italy 2 Department of Engineering and Geology, University ‘‘G. d’Annunzio’’, Chieti-Pescara, Italy Introduction. The 2009 L’Aquila earthquake (5.9 ML) boosted seismic microzonation studies within the SE part of the Aterno Valley where seismic Intensities higher than 6 MCS have been recognized. During this seismic event several towns and villages were threatened by multiple co-seismic phenomena (local amplification, liquefaction, landslide). The Italian guidelines for seismic microzonation do not clearly suggest any procedure to combine multiple co-seismic effects although a few scientists are currently developing procedures to manage multiple hazards and risks (Liu et al. , 2015 and references herein). The main aim of this study is to deal with two interfering co-seismic effects, namely the local seismic response LSR and the seismically induced landslides SL. To this end, LSR analyses carried out by a finite element method commercial code RSL 2D (Stacec, 2015) are planned to be combined to the seismically- induced rock sliding and falling at the study site of Casentino (located within Sant’Eusanio Forconese district, L’Aquila province). The scenario seismic event considered hereafter is the April 6, 2009 L’Aquila earthquake. The seismic microzoning of Casentino town. Casentino is a little town in Sant’Eusanio Forconese municipal area. It is located in central Italy, in L’Aquila province, in the heart of the Apennine territory. It is set into the Aterno Valley along the Eastern slopes of D’Ocre mountain range, between the steep limestone walls of the “MuroMurato” and the valley of “Fosso di Fossa “ (this latter is a tributary of the principal Aterno river). The authors performed Local Seismic Response LSR analyses through numerical simulations by finite element method FEM calculations. 1D (one-dimensional) and 2D (two-dimensional) numerical analyses have been performed to investigate the filtering effects of soil deposits overlaying the seismic bedrock on the seismic body waves (namely SH waves propagating within vertical one or two dimensional sections) in terms of amplitude, amplified periods and increased duration (detected were shear wave velocity V s >800 m/s). These effects are estimated on the ground surface where urban structures are mostly affected by the seismic induced horizontal vibrations. Fig. 1 – Two representative sections have been analyzed in order to obtain the amplification factors at Casentino urban area. Several geological, geotechnical and geophysical investigation campaigns have been used to reconstruct the stratigraphic successions and then the 2D sections. For each soil unit dynamic parameters have been measured and the equivalent linear behavior has been assumed.