Evidence of Topographic Effects through the Analysis of Ambient Noise Measurements

Panzera, Francesco; Lombardo, Giuseppe; Rigano, R.

doi:10.1785/gssrl.82.3.413

Cited by 41 publications

(21 citation statements)

References 33 publications

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“…Thus, they judged that "ambient noise is found to be a poor source for the study of topographic effects". With our study, we can confirm this observation, even though there are others (see, e.g., [20]) showing that topographic polarization effects can be analyzed though ambient vibration HVSR, at least if the site presents a clear ridge morphology and simple geological characteristics.…”

Section: The Use Of Hvsr For Site Effect Analysissupporting

confidence: 84%

“…Interestingly, the NS HVSR computed for S-wave windows of recorded earthquakes present clear low frequency peaks which, in addition, present a NS azimuth subparallel to the short axis of the hill (compare the NS with the EW S-waves HVSR in the graphs a2 and a1 of Figure 2). While ambient vibrations do apparently not help measure topographic effects, at least not those related to a more complex hill or mountain morphology (compared to the site presented by [20] that is marked by a clear ridge and unique lithology with uniform Vs 30 , Gros-Morne hill has a rough E-W elongation, but cannot be called a clear ridge, and Vs 15 values are highly variable over the hill), HVSR applied to S-wave windows of earthquake recordings, do. This might be due to the fact that ambient noise HVSR measures the ellipticity of surface waves, which are not necessarily affected by the global hill morphology (at least not if it is more complex), while the shaking of a mountain induced by an earthquake obviously affects, more intensely, the horizontal component along the short axis than the other horizontal component, and even more than the vertical component.…”

Section: The Use Of Hvsr For Site Effect Analysismentioning

confidence: 95%

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Site Effect Assessment of the Gros-Morne Hill Area in Port-au-Prince, Haiti, Part B: Mapping and Modelling Results

Ulysse

Boisson

Prépetit³

et al. 2018

Geosciences

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This paper presents the general results in terms of maps, as well as geological and numerical models of a site effect study, that aimed at a better understanding of the ground motion amplification on the Gros-Morne hill, in the southeastern part of Port-au-Prince, Haiti, which might have influenced the 2010 event damage pattern in that area. These maps and models are based on multiple geophysical-seismological survey outputs that are presented, in detail, in Part A of this publication. Those outputs include electrical resistivity tomography sections, P-wave velocity profiles, S-wave logs, estimates of the fundamental resonance frequency for many locations, as well as earthquake recordings at three sites and associated site amplification assessment for the top of the hill. Related results are discussed in Part A with respect to outputs and interpretations that had been published earlier by other research teams for the same site. Our results only partly confirm the strong seismic amplification effects highlighted by some of the previous studies for this hill site, which had been attributed to the influence of local topographic and soil characteristics on seismic ground motion. Here, we focus on the imaging of different site effect components over the entire survey area; we present maps of shear wave velocity variations, of changing fundamental resonance frequencies, and of related estimates of soft soil/rock thickness, of peak spectral amplitudes, and of ambient ground motion polarization. Results have also been compiled within a 3D surface-subsurface model of the hill, which helps visualize the geological characteristics of the area, which are relevant for site effect analyses. From the 3D geomodel, we extracted one 2D geological section along the short-axis of the hill, crossing it near the location of Hotel Montana on top of the hill, which had been destroyed during the earthquake, and has now been rebuilt. This cross-section was used for dynamic numerical modelling of seismic ground motion, and for related site amplification calculation. The numerical results are compared with the site amplification characteristics that had been estimated from the ambient vibration measurements and the earthquake recordings.

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Section: The Use Of Hvsr For Site Effect Analysissupporting

confidence: 84%

Section: The Use Of Hvsr For Site Effect Analysismentioning

confidence: 95%

Site Effect Assessment of the Gros-Morne Hill Area in Port-au-Prince, Haiti, Part B: Mapping and Modelling Results

Ulysse

Boisson

Prépetit³

et al. 2018

Geosciences

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show abstract

“…This approach, first applied to earthquake recordings in studying the directional effects due to topographic irregularities at Tarzana, California (Spudich et al, 1996), has been used for ambient noise signals by several authors (e.g. Lermo and Chávez-Garcia, 1993;Panzera et al, 2011a) and to identify site response directivity in the presence of an unstable slope as well (Del Gaudio et al, 2008;Burjánek et al, 2010;Del Gaudio and Wasowisky, 2011).…”

Section: Experimental Setup and Data Processingmentioning

confidence: 99%

Seismic site response of unstable steep slope using noise measurements: the case study of Xemxija Bay area, Malta

Panzera

D’Amico

Lotteri

et al. 2012

Nat. Hazards Earth Syst. Sci.

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Abstract. Landslide phenomena involve the northern coast of Malta, affecting in particular the urban area of Xemxija. Limestones overlying a clayey formation represent the shallower lithotypes that characterize the surficial geology of this area, where lateral spreading phenomena and rockfalls take place.Ambient noise records, processed through spectral ratio techniques, were analysed in order to characterize the dynamic behavior of the rock masses affected by the presence of fractures linked to the landslide body existing in the area. Experimental spectral ratios were also calculated after rotating the horizontal components of the seismic signal, and a direct estimate of the polarization angle was also performed in order to investigate the existence of directional effects in the ground motion.The results of the morphologic survey confirmed the existence of large cliff-parallel fractures that cause cliff-edge and unstable boulder collapses. Such phenomena appear connected to the presence, inside the clay formation, of a sliding surface that was identified through the interpretation of the noise measurement data. The boundaries of the landslide area appear quite well defined by the pronounced polarization effects, trending in the northeastern direction, observed in the fractured zone and in the landslide body in particular.

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“…Nevertheless, peaks of the HVSR in Piteglio (b and c in Fig. 4) occurred at frequencies which are higher than those expected, considering the Vs of the subsoil and the 400-800 m width of the hill [46,47]. Moreover, the EW/V and NS/V components of the HVSR are very similar, and do not exhibit any significant directionality (see panel b in Fig.…”

Section: Model Of the Subsoilmentioning

confidence: 75%

Preliminary seismic microzonation in a mountainmunicipality of Tuscany (Italy)

Matassoni¹,

Fiaschi²,

Silengo

et al. 2015

Open Geosciences

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Abstract:In this paper we describe a microzonation survey carried out at a mountain Municipality (Piteglio, Northern Apennines). We complemented the available data by conducting 106 microtremor measurements for Horizontal-toVertical Spectral Ratio (HVSR) analysis. Most of the data concern the three major rural villages (Piteglio-Prataccio, Popiglio and Prunetta). Furthermore, we installed a field mobile seismic station at two of the major villages, in order to obtain earthquakes recordings. The HVSR analysis shows amplification effects due to eluvial or colluvial deposits overlying the seismic bedrock, even for areas previously mapped as bedrock outcrops. Most zones characterized by sandstone outcrops show peaked HVSR traces. This observation could be also interpreted in terms of a topographic effect. In contrast, areas characterised by chaotic materials (olistostrome) generally exhibit a flat HVSR. Other areas of seismic amplification were identified on alluvial and landslide deposits. Results by HVSR analysis are well correlated with available data from geo-technical and geophysical surveys, thus allowing to invert HVSRs for the physical properties of the subsoil. Subsoil properties can thus be extrapolated also in areas for which only measurements of seismic noise are available. Moreover, noise HVSRs agree well with those from earthquakes recorded at the different selected sites.

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Evidence of Topographic Effects through the Analysis of Ambient Noise Measurements

Cited by 41 publications

References 33 publications

Site Effect Assessment of the Gros-Morne Hill Area in Port-au-Prince, Haiti, Part B: Mapping and Modelling Results

Site Effect Assessment of the Gros-Morne Hill Area in Port-au-Prince, Haiti, Part B: Mapping and Modelling Results

Seismic site response of unstable steep slope using noise measurements: the case study of Xemxija Bay area, Malta

Preliminary seismic microzonation in a mountainmunicipality of Tuscany (Italy)

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