Recent accelerometric recordings of earthquakes with moderate and intermediate magnitude (4.0 Ͻ M L Ͻ 5.9), at both local and regional distances, show a significant ground-motion amplification effect at low frequencies (0.6 Hz) in the city of L'Aquila (central Italy). The effect involves very long durations characterized by low frequencies in the coda. Starting from these observations, a series of supplementary investigations was performed in the urban area of L'Aquila by collecting and analyzing both weakmotion data from earthquakes with magnitudes ranging from 2.2 to 4.9 at distances from 20 to 105 km and ambient noise data. All the collected weak-motion data share the same characteristics as the strongmotion records and give a better image of the amplification effect in the city. In order to interpret observations in terms of the local geology, we performed 2D numerical modeling of the sedimentary basin underlying the city of L'Aquila using both finite elements and boundary elements based on a geological section derived from gravity measurements. This analysis indicates that the ground-motion amplification in the city of L'Aquila is related to the presence of a sedimentary basin, filled by lacustrine sediments, with a maximum depth of about 250 m. The combined approach to data collection and analysis used here gives useful information for risk assessment in the city of L'Aquila and can be recommended for many other urban areas that share similar characteristics.

The Italian Strong Motion Database, ITACA, was developed within projects S6 and S4, funded in the framework of the agreements between the Italian Department of Civil Protection (Dipartimento della Protezione Civile, DPC) and the Istituto Nazionale di Geofisica e Vulcanologia (INGV), starting from 2005. The alpha version of the database was released in 2007 and subsequently upgraded to version 1. 0 after: (i) including the most recent strong motion data (from 2005 to 2007) recorded in Italy, in addition to the 2008 Parma earthquake, M 5. 4, and the M ≥ 4. 0, 2009 Abruzzo seismic events; (ii) processing the raw strong motion data using an updated procedure; (iii) increasing the number of stations with a measured shear wave velocity profile; (iv) improving the utilities to retrieve time series and ground motion parameters; (v) implementing a tool for selecting time series in agreement with design-response spectra; (vi) compiling detailed station reports containing miscellaneous information such as photo, maps and site parameters; (vii) developing procedures for the automatic generation of station reports and for the updating of the header files. After such improvements, ITACA 1. 0 was published at the web site http://itaca.mi.ingv.it, in 2010. It presently contains 3,955 three-component waveforms, comprising the most complete catalogue of the Italian accelerometric records in the period 1972-2007 (3,562 records) and the strongest events in the period 2008-2009. Records were mainly acquired by DPC through its Accelerometric National Network (RAN) and, in few cases, by local networks and temporary stations or networks. This paper introduces the published version of the Italian Strong Motion database (ITACA version 1. 0) together with main improvements and new functionalities

A small size foreshock and the two mainshocks of the Umbria Marche earthquake sequence which occurred on September 26, 1997 have been recorded by two digital 3C accelerometers located at near source distances. The close epicentral distance and azimuthal location relative to the fault orientation and geometry make these records relevant to look at the detail of the rupture kinematics. S‐wave polarizations, apparent source time duration and waveforms from strong motion records are used to constrain the location of the fracture origin point, the fault geometry, the final slip distribution, size and mechanism of the events. The final model shows that the seismic ruptures occurred along two adjacent, sub‐parallel, low angle dipping normal faults. The relative timing, location and geometry of the mainshock faults suggest the presence of a transfer zone (barrier) which has probably controlled the amplitude increase of local stress released by the first rupture at its NW edge which triggered about 9 hours later the second rupture.

The Italian Strong Motion Network is a permanent monitoring system run by the Italian national emergency management department (Dipartimento della Protezione Civile, DPC). The network is known as RAN (Rete Accelerometrica Nazionale). An extensive project for updating and improving the technology of RAN instruments as well as the number of recording points was performed in the last 10 years. A wide site selection survey was carried out from eastern Sicily along the Italian peninsula, covering high seismic risk areas. The recording station density and the choice of high-quality digital strong motion instruments ensure reliability of the RAN network in the long-term. At the end of 2008, the free field sites selection and instruments installation, planned in the project, were quite completed. In planning and drawing the new RAN, special attention has been devoted to the robustness of the transmission systems, and to the distribution of new stations in order to ensure plenty of data during a seismic emergency. We spent special care both in the estimation of the RAN site responses and in the diffusion of the strong motion data. In order to better identify damaged earthquake areas, improved ground motion parameters need to be set. Such parameters will also assist future progress for engineering seismic design techniques as well as disaster mitigation.

The normal-faulting earthquake of 6 April 2009 in the Abruzzo Region of central Italy caused heavy losses of life and substantial damage to centuries-old buildings of significant cultural importance and to modern reinforced-concrete-framed buildings with hollow masonry infill walls. Although structural deficiencies were significant and widespread, the study of the characteristics of strong motion data from the heavily affected area indicated that the short duration of strong shaking may have spared many more damaged buildings from collapsing. It is recognized that, with this caveat of short-duration shaking, the infill walls may have played a very important role in preventing further deterioration or collapse of many buildings. It is concluded that better new or retrofit construction practices that include reinforced-concrete shear walls may prove helpful in reducing risks in such seismic areas of Italy, other Mediterranean countries, and even in United States, where there are large inventories of deficient structures.