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  • Articles  (7)
  • 04. Solid Earth::04.06. Seismology::04.06.06. Surveys, measurements, and monitoring  (3)
  • Nocera Umbra  (3)
  • ground motion
  • 1
    ISSN: 1573-157X
    Keywords: Nocera Umbra ; site effects ; weak motions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract During the ML = 5.6 and 5.8 earthquakes occurredin central Italy on 26 September 1997 the historiccentre of Nocera Umbra, lying on top of a 120 m highhill, was diffusely damaged (VII-VIII degrees of MCSintensity). Some recently built houses in the modernpart of the town suffered an even higher level ofdamage. A temporary seismic array was deployed toinvestigate a possible correlation between localamplifications of ground motion in this area and theobserved pattern of damage. After a geologic andmacroseismic survey, eight sites were selected asrepresentative of different local conditions, such astopographic irregularities, sharp hard-to-softlithology transitions, alluvium-filled valleys, andboth undisturbed and deformed rocks.Horizontal-to-vertical spectral ratios for bothmicrotremor and earthquake recordings, as well asspectral ratios referred to undisturbed rock sites,were used to quantify local variations of groundmotion. In spite of the diffuse damage in the historiccentre of Nocera Umbra, a small amplification isobserved at the stations on the hill's top. Thissuggests that the higher vulnerability of the ancientbuildings mainly accounts for the diffuse damage inthat part of the town. In the frequency band ofengineering interest (1 to 10 Hz) the largestamplifications of ground motion are found at softsites: in the Topino river valley, where many episodesof severe structural damage occurred, spectralamplification is significant over a broad frequencyband ranging from 2 Hz to more than 20 Hz. Inparticular, in the central part of the valley highamplification (〉 4) is found from 3 to 10 Hz,reaching a maximum of 20 around 4 Hz. At the edge ofthe valley, close to the soil-to-rock transition,amplification is as large as 10 in a frequency bandranging from 4 to more than 20 Hz. A significantamplification (by a factor of 10 around 10 Hz) isobserved also at one of the rock sites, possibly dueto the presence of a cataclastic zone related to theactivity of a regional fault that altered themechanical properties of the rock.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-157X
    Keywords: fault zone ; ground motion ; Nocera Umbra ; site effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract During the two mainshocks of September 26, 1997 inthe Umbria-Marche border a strong-motion accelerographrecorded peak ground accelerations as large as 0.6 g,approximately, in the town of Nocera Umbra, atdistances of 10 to 15 km from the epicentres. Thisvalue is significantly larger than expected on thebasis of the usual regressions with magnitude anddistance. A broad-band amplification up to a factor of10 was consistently estimated in previous papers,using both weak and strong motion data recorded at theaccelerograph site during local moderate earthquakes.To study the cause of this amplification we deployedsix seismologic stations across the tectonic contactbetween the Ceno-Mesozoic limestone and the Mesozoicmarly sandstone where the accelerograph is installed.Seismograms of 21 shallow aftershocks in the magnituderange from 2.2 to 4.0 and a subcrustal Mw = 5.3event are analysed. Regardless of epicentre location,waveforms show a large complexity in an approximately200 m wide band adjacent to the tectonic contact. Thisis interpreted as the effect of trapped waves in thehighly fractured, lower velocity materials within thefault zone.
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 2017-04-04
    Description: 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.
    Description: Published
    Description: 555-565
    Description: JCR Journal
    Description: reserved
    Keywords: site effects ; Nocera Umbra ; 04. Solid Earth::04.06. Seismology::04.06.04. Ground motion
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 4
    Publication Date: 2017-04-04
    Description: Moderate-magnitude shallow earthquakes in the Atlantic Ocean, hundreds of kilometres southwest of Lisbon, can generate efficient suboceanic Rayleigh waves (SRW) that are well recorded in Portugal. Here we compare moderate-size earthquakes recorded by seismic stations in Portugal with the Tyrrhenian Sea earthquakes recorded in peninsular Italy where SRW were recently observed. In spite of a different behaviour of high frequencies due to the different tectonic setting of the two areas, similar results are found in the intermediate-period range, suggesting that this effect, if extrapolated to a magnitude larger than 8, could be devastating at regional distance in terms of ground motion amplitude and duration. Through 1D models, we explore the hypothesis that the high level of destruction and the long duration of shaking felt during the Great 1755 Lisbon earthquake were caused by SRW. In this preliminary study, we check the role of critical model parameters. We find that duration and amplitude are largest when the average thickness of the water layer is 2 km and shear-wave velocity of the ocean floor is close to the speed of sound in the water. Both conditions are realistic for a source in the Atlantic Ocean, few hundreds of kilometres southwest of Lisbon. Moreover, the propagation of SRW at regional distances accounts for durations of more than ten minutes as the effect of a single large earthquake.
    Description: Published
    Description: 283-295
    Description: 4.1. Metodologie sismologiche per l'ingegneria sismica
    Description: open
    Keywords: ground motion ; surface waves ; 04. Solid Earth::04.06. Seismology::04.06.04. Ground motion
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: book chapter
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  • 5
    Publication Date: 2017-04-03
    Description: Seismic signals recorded in volcanic areas and associated with volcanic activity can be originated from many different sources. Among various types of transient signals, i.e., explosion quakes, tectonic quakes, long period events, those related to rockfall episodes are very important because rockfalls might contribute significantly to volcanic hazard even in areas characterized by volcanic quiescence. In this study we have analyzed the intracrateric rockfall events occurred since 2001 along the Vesuvius asymmetrical crater rim. Field investigations of the main morphostructural features carried out in the summit area, along with digital images collected during the study period, allowed us to infer the time evolution and the areal distribution of the rockfalls. Two main source areas located on opposite sides of the volcanic crater, to the NW and SSE, have been identi ed. Both of them are characterized by intense fracturing and fumarolic emissions. Seismic signals of the intracrateric rockfall events, recorded by the broadband and short-period permanent stations operated by the Osservatorio Vesuviano-INGV of Naples and located within a few kilometers from the crater, have been analyzed in terms of duration and frequency content in order to characterize the peculiar features of the source areas.
    Description: Published
    Description: Geneva, Switzerland
    Description: 5.5. TTC - Sistema Informativo Territoriale
    Description: open
    Keywords: ROCKFALLS, VESUVIUS VOLCANO, SEISMIC SIGNALS,MORPHOSTRUCTURAL STUDY ; 04. Solid Earth::04.06. Seismology::04.06.06. Surveys, measurements, and monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Abstract
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  • 6
    Publication Date: 2020-02-24
    Description: In this study, we investigate the mechanical properties of the substrate underlying the historical Franciscan Friars Minor convent of Ispica (southern Sicily). The convent, where new fractures recently occurred, is located on top of a calcarenite cliff formed along one of the planes of the regional Pozzallo-Ispica-Rosolini normal fault system. Taking advantage of three existing mechanical drillings 30 m deep, we have carried out down-hole tests (DHT) and a seismic tomography survey in up-hole configuration. The down-hole tests provided vertical profiles of P- and S-wave velocity measured at 1-m depth intervals, from which we have derived the basic elasto-dynamic and seismic parameters, while the tomography survey imaged vertical sections of P-wave velocity across the cliff. The results highlight variable mechanical properties of the subsoil and a step-like pattern of velocity variations parallel to the cliff face that could suggest the occurrence of secondary ruptures related to the main Ispica fault.
    Description: Published
    Description: 971–980
    Description: 6A. Monitoraggio ambientale, sicurezza e territorio
    Description: JCR Journal
    Description: reserved
    Keywords: down-hole tests, up-hole seismic tomography, Ispica, Sicily ; 04. Solid Earth::04.06. Seismology::04.06.06. Surveys, measurements, and monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 7
    Publication Date: 2019-11-04
    Description: JCR Journal
    Description: open
    Keywords: Tremiti deformation belt ; tectonic inversion ; 04. Solid Earth::04.06. Seismology::04.06.06. Surveys, measurements, and monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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