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Bellucci, Francesca
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Bellucci, Francesca
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- PublicationRestrictedLarge amplification of ground motion at rock sites within a fault zone in Nocera Umbra (central Italy)(2000)
; ; ; ; ; ; ; ; ; ;Marra, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Azzara, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Bellucci, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Caserta, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Cultrera, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Mele, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Palombo, B.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Rovelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Boschi, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione AC, Roma, Italia; ; ; ; ; ; ; ; During the two mainshocks of September 26, 1997 in the Umbria-Marche border a strong-motion accelerograph recorded peak ground accelerations as large as 0.6 g, approximately, in the town of Nocera Umbra, at distances of 10 to 15 km from the epicentres. This value is significantly larger than expected on the basis of the usual regressions with magnitude and distance. A broad-band amplification up to a factor of 10 was consistently estimated in previous papers, using both weak and strong motion data recorded at the accelerograph site during local moderate earthquakes. To study the cause of this amplification we deployed six seismologic stations across the tectonic contact between the Ceno-Mesozoic limestone and the Mesozoic marly sandstone where the accelerograph is installed. Seismograms of 21 shallow aftershocks in the magnitude range from 2.2 to 4.0 and a subcrustal Mw = 5.3 event are analysed. Regardless of epicentre location, waveforms show a large complexity in an approximately 200 m wide band adjacent to the tectonic contact. This is interpreted as the effect of trapped waves in the highly fractured, lower velocity materials within the fault zone.313 31 - PublicationOpen AccessMETODI PER LA STIMA DEGLI EFFETTI DI SITO(2001-03)
; ; ; ;Bellucci, Francesca; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Cara, Fabrizio; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Di Giulio, Giuseppe; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; ; 171 289 - PublicationRestrictedStudy of site effects in the area of Nocera Umbra (central Italy) during the 1997 Umbria-Marche seismic sequence(2000)
; ; ; ; ; ; ; ; ;Caserta, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Bellucci, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Cultrera, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Donati, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Marra, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Mele, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Palombo, B.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Rovelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; ; ; ; ; ; ; During the ML = 5.6 and 5.8 earthquakes occurred in central Italy on 26 September 1997 the historic centre of Nocera Umbra, lying on top of a 120 m high hill, was diffusely damaged (VII-VIII degrees of MCS intensity). Some recently built houses in the modern part of the town suffered an even higher level of damage. A temporary seismic array was deployed to investigate a possible correlation between local amplifications of ground motion in this area and the observed pattern of damage. After a geologic and macroseismic survey, eight sites were selected as representative of different local conditions, such as topographic irregularities, sharp hard-to-soft lithology transitions, alluvium-filled valleys, and both undisturbed and deformed rocks. Horizontal-to-vertical spectral ratios for both microtremor and earthquake recordings, as well as spectral ratios referred to undisturbed rock sites, were used to quantify local variations of ground motion. In spite of the diffuse damage in the historic centre of Nocera Umbra, a small amplification is observed at the stations on the hill’s top. This suggests that the higher vulnerability of the ancient buildings mainly accounts for the diffuse damage in that part of the town. In the frequency band of engineering interest (1 to 10 Hz) the largest amplifications of ground motion are found at soft sites: in the Topino river valley, where many episodes of severe structural damage occurred, spectral amplification is significant over a broad frequency band ranging from 2 Hz to more than 20 Hz. In particular, in the central part of the valley high amplification (> 4) is found from 3 to 10 Hz, reaching a maximum of 20 around 4 Hz. At the edge of the valley, close to the soil-to-rock transition, amplification is as large as 10 in a frequency band ranging from 4 to more than 20 Hz. A significant amplification (by a factor of 10 around 10 Hz) is observed also at one of the rock sites, possibly due to the presence of a cataclastic zone related to the activity of a regional fault that altered the mechanical properties of the rock.289 27