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In this paper, we present 3D physics-based numerical simulations, in the near-source region at the regional scale, of the 2009, April 6, L'Aquila earthquake (central Italy), based on improved models of the Aterno river basin geology and source kinematics. The simulations were carried out by an open-source code, SPEED, based on a discontinuous Galerkin spectral element method. The numerical mesh of the Aterno basin was built on a detailed subsurface geological model and on the evaluation of the dynamic properties of the soils. The source model was selected among the kinematic solutions available in the literature as the one that fits best the near-source observations. Broadband ground motions were then generated through a hybrid method, combining 3D low frequency waveforms with high-frequency stochastic synthetics. To provide an example of application as seismic input to earthquake engineering analyses in the time domain, results of this approach were used for 2D site response analyses at Castelnuovo, a village severely damaged by the earthquake, and in the neighborhood of which no seismic record was available. SPEED simulation satisfactorily reproduces the recorded accelerograms in the frequency range 0.1-0.7 Hz. The site response analysis at the local scale shows that the amplification of the hill is more significant at its natural frequency, due to topographic and stratigraphic factors, than at the peak of the seismic input simulated by SPEED, that is at about 3 s along the fault-normal component. The presented application supports the conclusion that 3D physics-based numerical simulations do have the potential to become an alternative for determination of input ground motion for earthquake engineering analyses, especially for those scenarios for which real records are not available. [ABSTRACT FROM AUTHOR]

During the Abruzzo earthquake (6.IV.2009, M = 6.3), the village of Castelnuovo, lying on an elliptical hill about 60 m high, underwent an intensive damage (I = 9-10), that could be partly ascribed to the topographic amplification and to the presence of an underground cavity network. To verify these hypotheses, the seismic response of the hill was carefully investigated adopting both 2D and 3D finite difference numerical models. Analyses were carried out using a detailed geotechnical model, defined on the basis of a comprehensive field investigation (boreholes, DH, HVSR, ERT) and accurate laboratory tests (RC-TS). The reference input motion was reproduced considering the time history of the mainshock recorded at an accelerometric station close to the epicenter, conveniently deconvoluted to the bedrock and scaled in amplitude to the site of Castelnuovo. The results of the numerical analyses, expressed in terms of distribution of the amplification factor of peak acceleration and Housner intensity, proved that the topographic effects significantly influenced the ground motion at surface, whereas the role of cavities seemed to be negligible. [ABSTRACT FROM AUTHOR]

The surface wave method is a characterization technique that allows obtaining the shear wave velocity profiles trough the measurement of the dispersion of surface waves coupled with an inversion procedure. Spectral and multichannel analysis of surface wave techniques are becoming, recently, a common investigation tool for site characterization. For the inversion of the surface wave dispersion curve, homogeneous or horizontally layered soil models are assumed and this hypothesis could represent a limitation on the practical use of the technique. In this paper, the numerical dispersion curves of a subsoil, constituted by two layers of elastic material separated by a horizontal or an inclined interface, are simulated by a finite element commercial code. This allows detecting some limits in the conventional interpretation of the surface wave tests. MASW experiments executed in two different sites in Molise Region (Italy), characterized by simple or complex stratigraphic conditions, are shown as examples to validate the assumption and the analyses made in the paper. [ABSTRACT FROM AUTHOR]