Strong Ground Motion in the Epicentral Region of the M\u3csub\u3ew\u3c/sub\u3e 6.3, Apr 6 2009, L’Aquila Earthquake, Italy

In the night of Apr 6 2009, a Mw 6.3 earthquake struck the Abruzzi region and the whole Central Italy, causing about 300 deaths and vast destructions in the town of L\u27Aquila, one of the largest urban centres in Central Italy, and its surroundings. As most destructive earthquakes in the Italian Central and Southern Apennines mountain chain, this was caused by a normal fault rupture, the epicenter of which was estimated at less than 5 km from the center of L\u27Aquila. Several 3-components digital strong motion instruments were installed around L\u27Aquila at few km distance from the epicenter: 3 of them recorded the earthquake along a transept crossing the Aterno river valley, while two of them are located in the town centre. The near-fault conditions, the complex geological setting – L\u27Aquila lies on a fluvial terrace, consisting of calcareous breccias and conglomerates, lying on the top of lacustrine silty sediments – and the availability of several very good quality near-fault records, make this earthquake an important benchmark that provided an impressive and instructive picture of strong ground motion in the epicentral region of a normal fault earthquake. This paper illustrates some of the most interesting features of the L\u27Aquila earthquake near-fault dataset, including (i) peak values and spectral ordinates, together with their relationship with respect to some of the most up-to-date ground motion prediction equations, (ii) long period components, (iii) vertical vs horizontal ground motion. Finally, since the L\u27Aquila shallow subsoil is characterized by frequent natural buried cavities of karst origin, we briefly investigate their potential role on the seismic response

Selection and spectral matching of recorded ground motions for seismic fragility analyses

Ground motion selection is one of the most important phases in the derivation of fragility curves through non-linear dynamic analyses. In this context, an easy-to-use software, namely S&M—Select & Match, has been adopted for the selection and spectral matching of recorded ground motions approaching a target response spectrum in a broad period range. In this paper, after a brief description of the key features of the S&M tool, two sets of 125 accelerograms, separately for stiff (i.e. site classes A and B according to the Italian code) and soft soil (i.e. site classes C and D) conditions, have been selected on the basis of the elastic design spectra of the Italian seismic code defined for different return periods. The selected ground motions have been analysed and used for non-linear dynamic analysis of a case study representative of a common Italian RC building type designed only to gravity loads. Results have been analysed in order to check the capability of the considered signals to adequately cover all the damage levels generally adopted in seismic risk analyses, as well as the effects on seismic response due to the selection criteria permitted by the proposed tool

Topographic amplification from recorded earthquake data and numerical simulations

With the aim of contributing to the refinement of the next generation of tools for seismic hazard analyses, we present here an attempt at including topographic amplification factors in GMPEs, thus broadening the traditional options for site effects. With a view to critically discuss and complement with new data the approach of Cauzzi et al. (2010) and Paolucci (2002), information from additional numerical models including crustal layering are taken into account. The indications obtained from the numerical simulations are cross-checked against and consolidated by analyses of the residuals of a selection of strong- and weak-motion observations on topographic reliefs in Italy and Switzerland (carefully selected via GIS) with respect to a set of largely used GMPEs

Anatomy of strong ground motion: near-source records and three-dimensional physics-based numerical simulations of the Mw 6.0 2012 May 29 Po Plain earthquake

Stimulated by the recent advances in computational tools for the simulation of seismic wave propagation problems in realistic geologic environments, this paper presents a 3D physicsbased numerical study on the prediction of earthquake ground motion in the Po Plain, with reference to the MW 6.0 May 29 2012 earthquake. To respond to the validation objectives aimed at reproducing with a reasonable accuracy some of the most peculiar features of the nearsource strong motion records and of the damage distribution, this study required a sequence of investigations, starting from the analysis of a nearly unprecedented set of near-source records, to the calibration of an improved kinematic seismic source model, up to the development of a 3D numerical model of the portion of the Po Plain interested by the earthquake, including the irregular buried morphology, with sediment thickness varying from few tens of m to some km. The spatial resolution of the numerical model is suitable to propagate up to about 1:5 Hz. Numerical simulations were performed using the open-source high-performance code SPEED, based on the Discontinuous Galerkin Spectral Elements (DGSE) method. The 3D numerical model coupled with the updated slip distribution along the rupturing fault proved successful to reproduce with reasonable accuracy, measured through quantitative goodness-of-fit criteria, the most relevant features of the observed ground motion both at the near- and far-field scales. These include: (i) the large fault normal velocity peaks at the near-source stations driven by updip directivity effects; (ii) the small-scale variability at short distance from the source, resulting in the out-of-phase motion at stations separated by only 3 km distance; (iii) the propagation of prominent trains of surface waves, especially in the Northern direction, induced by the irregular buried morphology in the near-source area; (iv) the map of earthquake-induced ground uplift with maximum values of about 10 cm, in substantial agreement with satellite measurements; and (v) the two-lobed pattern of the peak ground velocity map, well correlated with the distribution of macroseismic intensity