Abstract

Strong motion data during the L’Aquila seismic sequence, were mainly recorded by the Italian accelerometric network (Rete Accelerometrica Nazionale, RAN), operated by the Department of Civil Protection (DPC). Several records were obtained also by a temporary network installed the day after the mainshock by the Istituto Nazionale di Geofisica e Vulcanologia (INGV). The L’Aquila earthquake is the third strongest seismic event producing strong-motion records in Italy, after the Irpinia (1980, M_w 6.9) and Friuli (1976, M_w 6.4) earthquakes. This event, together with its largest aftershocks (Mw > 4.0) provided a unique strong-motion data set in Italy, especially due to the amount and intensity of near-fault records. The data set included in the Italian strong motion database, ITACA, consists of about 300 digital accelerograms (270 of which belonging to RAN), with a very good signal-to-noise ratio, recorded by about 70 stations, installed on different site conditions at distances ranging from 0 to 300 km. The national and international relevance of this data set is enhanced by its contribution to filling gaps in the magnitude-distance distribution of worldwide strong motion records, especially for normal-fault earthquakes. Near-fault records were obtained by (i) an array of 6 stations installed by DPC in 2001 in the Aterno Valley to study seismic site effects; (ii) station AQK close to downtown L’Aquila; (iii) station AQU, belonging to the broad-band Mednet network, located in the L’Aquila historic castle; (iv) the stations of the INGV temporary network, installed in the epicentral region one day after the mainshock. These stations are located less than 5 km from the mainshock epicenter and are inside the surface projection of the fault rupture. This work presents an overview of the main features of seismic ground shaking during the L&csquo;Aquila sequence, referring to records of the mainshock and of the two strongest aftershocks. The dependence of the strong-motion parameters on distance, azimuth and site conditions as well as the characteristics of near-fault strong-motion records are discussed.

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