Far-Source Long Period Displacement Response Spectra in the Venetian and Po plains (Italy) from 3D Wavefield Simulations

Speaker: Alessandro Vuan
The formulation of design elastic displacement spectra for seismic codes, and zoning studies of seismic hazard for long-period structures are becoming of crucial importance in modern earthquake engineering. The growing diffusion of displacement-based design approaches together with the availability of good quality digital strong motion data has allowed to obtain reliable spectral shapes for seismic design up to 10 s. However additional studies have still to be accomplished especially in deep sedimentary basins and plains to investigate site amplification effects during large levels of shaking and to infer the resulting displacement response spectra shape (DRS). Large amplitude long-period waves from distant large earthquakes can provide enough energy to excite the deep sedimentary basin structure. Existing accelerometric seismic networks are normally deployed on rock soil type and data recorded within deep basins (having a good seismic site characterization) from large earthquakes are difficult to find in the international databases. Here we focus on the numerical modeling of 3-D wave-field in 1D flat layered and 3D structures in the Po and Venetian plains (Italy). Modeling is needed because of the lack of recordings of mediumstrong earthquakes within deep soft sediments. We investigate earthquakes with magnitudes larger than M = 6.5 and hypocentral distances greater than 50 km. The main results are represented by: 1) the estimation of expected DRS in the period range from 1 to 10 s in the Po and Venetian plains, 2) the comparison between the DRS resulting from different numerical simulations (flat layered and 3D structures) and the uniform hazard DRS available for Italy and, 3) the evaluation of the influence of deep sediments in DRS shape to eventually implement this effect in seismic codes. Moreover 1D and 3D simulated DRS are compared with DRS obtained from recordings in the Kanto basin where similar long period displacement is observed.