Site Amplifications Observed in the Gubbio Basin, Central Italy: Hints for Lateral Propagation Effects

Self Cite

Experimental data and numerical modelling were used to study the effect of local geology on the seismic response of the Catania area. The town extends on a marly clays bedrock and terraced deposits made up by coastal sands and alluvial conglomerates. This sedimentary substratum is deeply entrenched by paleo-valleys filled by lava flows and pyroclastics. Available borehole data and elastic parameters were used to reconstruct a geotechnical model in order to perfome 1D numerical modeling. Seismic urban scenarios were simulated considering destructive (M w = 7.0), strong (M w = 6.2) and moderate (M w = 5.7) earthquakes to assess the shaking level of the different outcropping formations. For each scenario seven real accelerograms were selected from the European Strong Motion Database to assess the expected seismic input at the bedrock. PGA and spectral acceleration at different periods were obtained in the urban area through the equivalent linear numerical code EERA, and contour maps of different levels of shaking were drawn. Standard and horizontal-to-vertical spectral ratios were achieved making use of a dataset of 172 seismic events recorded at ten sites located on the main outcropping lithotypes. Spectral ratios inferred from earthquake data were compared with theoretical transfer functions. Both experimental and numerical results confirm the role of the geological and morphologic setting of Catania. Amplification of seismic motion mainly occurs in three different stratigraphic conditions: (a) sedimentary deposits mainly diffused in the south of the study area; (b) spots of soft sediments surrounded by lava flows; (c) intensely fractured and scoriaceous basaltic lavas.

Section: Resultsmentioning

confidence: 99%

The role of alternating outcrops of sediments and basaltic lavas on seismic urban scenario: the study case of Catania, Italy

Panzera

Rigano

Lombardo

et al. 2010

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“…This wide amplification can be traced back to a number of causes, i.e. a low impedance contrast, some irregular underground interfaces or in general 2-D or 3-D effects as well as the effects of locally induced surface waves as observed by Bindi et al (2009bBindi et al ( , 2011b at sites located on alluvial basins. Since the village of Pretare is built on the deposits of an ancient landslide, with a varying laterally thickness, and we do not observe any evidence of significant surface wave contribution in the recordings, we can just hypothesize that this amplification is due to the local heterogeneity of the underground structure.…”

Section: Spectral Amplificationmentioning

confidence: 99%

The Central Italy 2016–2017 seismic sequence: site response analysis based on seismological data in the Arquata del Tronto–Montegallo municipalities

Laurenzano

Barnaba

Romano

et al. 2018

In this paper we evaluate the local seismic response for thirteen sites located in the municipalities of Arquata del Tronto and Montegallo, two areas which suffered heavy damage during the Mw 6.0 and Mw 5.4 earthquakes which struck Central Italy on August 24, 2016. The input dataset is made by ground motion recordings of 348 events occurred during the sequence. The spectral site response is estimated by the Generalized Inversion Technique and makes use of reference sites. The interpretation is further improved through the information provided by a reference-site independent method (i.e., the so called Receiver-Function Technique) and by the Horizontal-to-Vertical Spectral Ratios of ambient noise recordings. We also provide an independent estimate of the local amplification by comparing the Peak Ground Velocity and the Spectral Amplitudes observed at each site to the value estimated by well-established Ground Motion Prediction Equations for a rock-class site. The results obtained by the adopted methodologies are all highly consistent, and they emphasize the different seismic behavior of several sites at local scale. Thus, sites located on Quaternary deposits overlying the bedrock, such as Castro, Pretare, Spelonga, Pescara del Tronto, and Capodacqua feature some relevant amplifications in a medium (2-10 Hz) frequency range; two sites at Spelonga show amplifications also at low frequencies; three sites located on stiff formations, i.e. Uscerno, Balzo and Colle d'Arquata, respectively, feature either nearly neutral response or low amplification level. A probable topographic effect was identified at the rock site of Rocca di Arquata (MZ80).

“…The HVSR method has been used for site effects assessment in various geomorphological cases and microzonation studies (e.g Chavez-Garcia et al 1995;Teves-Costa et al 1996;Bard 1998;Mucciarelli et al 2003a;Cara et al 2003;Bindi et al 2009;Beroya et al 2009;Gallipoli et al 2011;Strollo et al 2011;Puglia et al 2011;Mucciarelli 2011). HVSR has been also applied in several Basins indicating the contribution of the local geomorphology on seismic ground motion (e.g Teves-Costa et al 1996;Gueguen et al 2000;Lebrun et al 2001;Gosar 2007;Bonnefoy-Claudet et al 2008;Özalaybey et al 2011 ;).…”

Section: Brief Literature Reviewmentioning

confidence: 99%

“…Strollo et al (2011) for the case study of microzonation in Potenza (Italy) compared HVSR, SSR and GIT and found good correlation of the results while at one site the differences in the amplification was ascribed to the amplification in the vertical component. Bindi et al 2009 applied time-frequency analysis in earthquake data recorded in Gubbio Basin (Italy) and showed the dispersive behavior of the large amplitudes arrivals after the S-waves which suggested the contribution of the locally generated Rayleigh waves in determining large ground motion amplitude of the vertical component. 2D/3D effects of the Gubbio Basin inserted locally generated Basin-induced waves which amplify the vertical component and affect the HVSR amplitude.…”

Section: Fig11mentioning

confidence: 99%

Seismic site characterization of the Kastelli (Kissamos) Basin in northwest Crete (Greece): assessments using ambient noise recordings

Moisidi

Vallianatos

Kershaw

et al. 2014

Crete is actively seismic and site response studies are needed for estimating local site conditions subjected to seismic activity. In order to collect basic data, we performed ambient noise recordings to estimate the site response of the surface and near subsurface structure of the small-scale Kastelli Basin in northwest Crete. The spatial HVSR resonance pattern of the investigated sites in the centre of the Basin consists of either one or two peaks divided into low to high frequency range in different sites as follows: a) in some sites only one amplified peak at low frequencies (0.59 -1.23 Hz), b) in other sites only one amplified peak at medium frequencies (2.9 -8.54 Hz) and c) in yet other sites two amplified peaks in the low to high frequency range (0.59 -15.54 Hz). The investigated sites are amplified in the frequency range 0.59 -15.54 Hz while the amplitude reaches to a factor of 4 in the spectral ratios. The one HVSR amplified peak at low frequencies is related to locally soft or thick Quaternary deposits.Microtremors were measured in the coastal northwest part of the Basin in a well -lithified Cretaceous limestone site characterized by fractures and faults striking predominantly in a sector NNE to NNW. Sites of one amplified peak at medium frequencies are extended from coastal northwest to southwest delineating a structure striking to NNW. The two amplified peaks are attributed to shallow subsurface heterogeneities/irregularities, locally induced by fault zones and to the overlying Quaternary deposits.Spatial HVSR variations in the frequency and HVSR shape delineate four structures striking NNE, NNW and in a sector NW to WNW, crosscutting the dense populated Basin, suggesting that microtremors could be a valuable tool for providing a first approximation of fault zone delineation at least for the KastelliKissamos Basin. The Basin is classified into the X soil category of the Greek Seismic Code 2000.