Fieldwork on local-site seismic response in the Po Plain: examples from ambient vibration array and single station analyses

2016 ◽  
Vol 15 (6) ◽  
pp. 2349-2366 ◽  
Author(s):  
M. Massa ◽  
C. Mascandola ◽  
C. Ladina ◽  
S. Lovati ◽  
S. Barani
Keyword(s):  
Seismic Response ◽  
Ambient Vibration ◽  
Po Plain ◽  
Local Site ◽  
Single Station

Reconstruction of a Reference Subsoil Model for the Seismic Microzonation of Gori (Georgia): A Procedure Based on Principal Component Analysis (PCA)

2021 ◽  
Author(s):  
Silvia Giallini ◽  
Enrico Paolucci ◽  
Pietro Sirianni ◽  
Dario Albarello ◽  
Iolanda Gaudiosi ◽  
...  
Keyword(s):  
Principal Component Analysis ◽  
Seismic Response ◽  
Principal Component ◽  
Component Analysis ◽  
Vibration Monitoring ◽  
Ambient Vibration ◽  
Geological Evidence ◽  
Local Seismic Response ◽  
Geophysical Surveys ◽  
Single Station

ABSTRACT This article focuses on the full exploitation of geological and economically viable geophysical surveys for the seismic characterization of the shallow subsoil in the frame of microzonation studies in urban areas where economic resources for detailed seismic response analyses are scarce. In these conditions, the outcomes of inexpensive geophysical surveys (e.g., based on ambient vibration monitoring or surface-wave prospecting) must be fully exploited. To reduce the uncertainties related to these kinds of procedures, their joint interpretation in the light of geological evidence is mandatory. To this purpose, we propose the application of principal component analysis to combine the results of distributed single-station ambient vibration measurements (horizontal-to-vertical spectral ratio [HVSR] technique) to provide a preliminary zonation of the study area. The zones identified in this way are then characterized by considering the available geognostic boreholes, VS profiles deduced by the joint inversion of HVSR curves, and available Rayleigh-wave dispersion curves deduced from active seismic prospecting (multichannel analysis of surface-waves technique). The final outcome allows the definition of a preliminary seismic model of the study area, which is also constrained by the available geological data deduced from on-purpose surveys. The proposed approach has been applied to the city of Gori (Georgia). The proposed approach allowed a reliable assessment of buried geometries, geological domains, and the distribution of lithofacies, which can control the local seismic response. In detail, the major role of paleovalley infills and interfluve domains has been enlightened by adding in evidence concerning the peculiar stratigraphic relationships and buried morphologies, which may determine 1D and 2D resonance effects.

scholarly journals Regional Seismic Characterization of Shallow Subsoil of Northern Apulia (Southern Italy)

Geosciences ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 416
Author(s):  
Enrico Paolucci ◽  
Giuseppe Cavuoto ◽  
Giuseppe Cosentino ◽  
Monia Coltella ◽  
Maurizio Simionato ◽  
...  
Keyword(s):  
Southern Italy ◽  
Carbonate Platform ◽  
Low Cost ◽  
Principal Component ◽  
Ambient Vibration ◽  
Resonance Effects ◽  
Resonance Phenomena ◽  
Single Station ◽  
Seismic Characterization

A first-order seismic characterization of Northern Apulia (Southern Italy) has been provided by considering geological information and outcomes of a low-cost geophysical survey. In particular, 403 single-station ambient vibration measurements (HVSR techniques) distributed within the main settlements of the area have been considered to extract representative patterns deduced by Principal Component Analysis. The joint interpretation of these pieces of information allows the identification of three main domains (Gargano Promontory, Bradanic Through and Southern Apennines Fold and Thrust Belt), each characterized by specific seismic resonance phenomena. In particular, the Bradanic Through is homogeneously characterized by low frequency (<1 Hz) resonance effects associated with relatively deep (>100 m) seismic impedance, which is contrasting corresponding to the buried Apulian carbonate platform and/or sandy horizons located within the Plio-Pleistocene deposits. In the remaining ones, relatively high frequency (>1 Hz) resonance phenomena are ubiquitous due to the presence of shallower impedance contrasts (<100 m), which do not always correspond to the top of the geological bedrock. These general indications may be useful for a preliminary regional characterization of seismic response in the study area, which can be helpful for an effective planning of more detailed studies targeted to engineering purposes.

scholarly journals Geotechnical characterization and seismic response of shallow geological formations in downtown Lisbon

2014 ◽  
Vol 57 (4) ◽  
Author(s):  
Paula Teves-Costa ◽  
Isabel M. Almeida ◽  
Isabel Rodrigues ◽  
Rita Matildes ◽  
Claudia Pinto
Keyword(s):  
Seismic Response ◽  
Fundamental Frequency ◽  
Linear Method ◽  
Ambient Vibration ◽  
Building Stock ◽  
Alluvial Deposits ◽  
Amplification Factors ◽  
Geotechnical Characterization ◽  
Geotechnical Database

<p> </p><p>The geological and geotechnical characterization of shallow formations is one of the main steps in performing a microzonation study. This paper presents an example of the usefulness of the information compiled in a geological and geotechnical database for the estimation of the seismic response of the shallower formations of the Lisbon downtown area of Baixa. The geotechnical characterization of this area was performed based on the analysis of Standard Penetration Test (SPT) data compiled in the geological and geotechnical database. This database, connected to a geoscientific information system (CGIS), allows, also, the definition of 2D geological profiles used for estimating the thickness of the shallower layers. The shear-wave velocities (V<span><sub>S </sub></span>) for each layer were estimated from empirical correlations using mean SPT values computed from the statistical evaluation of the compiled data. These V<span><sub>S</sub></span> values were further calibrated with ambient vibration recording analysis. The seismic response of Baixa’s superficial deposits was estimated by applying a 1D equivalent linear method to a set of soil profiles, regularly distributed across the area, and using synthetic accelerograms to simulate input motions associated with probable earthquake occurrences in Lisbon. The results are presented in terms of maps of predominant frequencies, with the corresponding amplification level, as well as spectral amplification factors for 1 Hz and 2.5 Hz. The results show that the fundamental frequency of the Baixa area is between 1.2 Hz and 2 Hz, for the whole central valley, reaching 3 Hz near the edges where anthroprogenic and alluvial deposits have less expression. Amplification factors up to 5 were obtained. These results were achieved regardless of the considered input motion. The similarity of the obtained fundamental frequency with the natural frequency of Baixa’s old building stock increases the probability of resonance effects in future earthquakes.</p><p><span style="font-size: medium;"><br /></span></p>

scholarly journals Physical stratigraphy and geotechnical properties controlling the local seismic response in explosive volcanic settings: the Stracciacappa maar (central Italy)

2020 ◽  
Vol 80 (1) ◽  
pp. 179-199
Author(s):  
M. Moscatelli ◽  
G. Vignaroli ◽  
A. Pagliaroli ◽  
R. Razzano ◽  
A. Avalle ◽  
...  
Keyword(s):  
Seismic Response ◽  
Ground Motion ◽  
Central Italy ◽  
Volcanic Event ◽  
Ground Motion Amplification ◽  
Local Seismic Response ◽  
Single Station ◽  
Seismic Scenarios ◽  
Physical Stratigraphy ◽  
Subsoil Model

AbstractNowadays, policies addressed to prevention and mitigation of seismic risk need a consolidated methodology finalised to the assessment of local seismic response in explosive volcanic settings. The quantitative reconstruction of the subsoil model provides a key instrument to understand how the geometry and the internal architecture of outcropping and buried geological units have influence on the propagation of seismic waves. On this regard, we present a multidisciplinary approach in the test area of the Stracciacappa maar (Sabatini Volcanic District, central Italy), with the aim to reconstruct its physical stratigraphy and to discuss how subsoil heterogeneities control the 1D and 2D local seismic response in such a volcanic setting. We first introduce a new multidisciplinary dataset, including geological (fieldwork and log from a 45-m-thick continuous coring borehole), geophysical (electrical resistivity tomographies, single station noise measurements, and 2D passive seismic arrays), and geotechnical (simple shear tests performed on undisturbed samples) approaches. Then, we reconstruct the subsoil model for the Stracciacappa maar in terms of vertical setting and distribution of its mechanical lithotypes, which we investigate for 1D and 2D finite element site response analyses through the application of two different seismic scenarios: a volcanic event and a tectonic event. The numerical modelling documents a significant ground motion amplification (in the 1–1.5 Hz range) revealed for both seismic scenarios, with a maximum within the centre of the maar. The ground motion amplification is related to both 1D and 2D phenomena including lithological heterogeneity within the upper part of the maar section and interaction of direct S-waves with Rayleigh waves generated at edges of the most superficial lithotypes. Finally, we use these insights to associate the expected distribution of ground motion amplification with the physical stratigraphy of an explosive volcanic setting, with insights for seismic microzonation studies and local seismic response assessment in populated environments.

Geopsy: A User-Friendly Open-Source Tool Set for Ambient Vibration Processing

2020 ◽  
Vol 91 (3) ◽  
pp. 1878-1889 ◽  
Author(s):  
Marc Wathelet ◽  
Jean-Luc Chatelain ◽  
Cécile Cornou ◽  
Giuseppe Di Giulio ◽  
Bertrand Guillier ◽  
...  
Keyword(s):  
Open Source ◽  
User Interfaces ◽  
Site Characterization ◽  
Ambient Vibration ◽  
The European Union ◽  
Vibration Data ◽  
Single Station ◽  
Characterization Studies ◽  
Single Trace ◽  
User Friendly

Abstract Ambient vibrations are nowadays considerably used worldwide for numerous types of engineering applications and scientific research. Geopsy and its companion tools are part of that landscape. Since the first release of the program package in 2005, as outcome of the European Union project Site Effects aSsessment from AMbient noisE, Geopsy has become a mature multiplatform open-source package (released under GNU Public License version 3) that has already been recognized as a reference tool for analyzing ambient vibration data in the context of site characterization studies. The community of users has grown from a core group of researchers up to thousands of seismologists and engineers on every career level and on all continents. The versatility of geopsy allows for the processing of all kinds of data needed in site characterization studies, that is, from single station single trace to three-component array recordings. In all of the aforementioned cases, the steps from field acquisition to the production of publication-ready figures are covered and supported by user-friendly graphical user interfaces or corresponding command-line tools for the automation of the complete processing chain. To avoid black-box usage, a number of lower-level tools guarantee maximum flexibility in accessing and controlling processing results at any stage of the analysis.

Characterization of unstable rock slopes using ambient vibration analysis

2020 ◽  
Author(s):  
Donat Fäh ◽  
Mauro Häusler ◽  
Franziska Glueer ◽  
Jan Burjanek ◽  
Ulrike Kleinbrod
Keyword(s):  
Seismic Response ◽  
Normal Mode ◽  
Wave Velocity ◽  
Ambient Vibration ◽  
Mode Analysis ◽  
Permafrost Degradation ◽  
Rock Slopes ◽  
Spectral Ratios ◽  
S Wave

&lt;p&gt;Earthquake-induced landslides can have serious social impacts, causing many casualties and significant damage to infrastructure. They are the most destructive secondary hazards related to earthquakes. The impact of strong seismic events is not limited just to triggering of catastrophic slope failures, it also involves weakening of intact rock masses and reactivation of dormant slides. Hazard mitigation of potentially catastrophic landslides requires a thorough understanding of the mechanisms driving slope movements and seismic response.&lt;/p&gt;&lt;p&gt;We present an overview of the investigations on more than 25 instabilities. The results show that ambient vibration measurements allow for a rapid and objective characterization of potential slope instabilities. It is possible to distinguish unstable from stable areas, to identify slope eigen-frequencies, local amplification levels due to weak excitation, local deformation directions and properties of the internal slope structure. The ambient vibration techniques include single-station H/V ratios and polarization analyses, site-to-reference spectral ratios, array methods to identify surface-wave dispersion curves, and/or normal mode analysis using enhanced frequency domain decomposition. We analyse the seismic response of the rock slopes in different frequency bands together with its spatial and azimuthal variability, which is a fingerprint of the slope&amp;#8217;s internal structure at different scales (tenth of meters to hundred meters). Normal mode behaviour is typically observed in structures with distinct sub-volumes, where the wave field at the resonance frequencies is oriented perpendicular to the deep persistent fractures. These structures show maximum amplification at their resonance frequency. Normal mode behaviour is also observed for rock towers, similar to what can be observed for buildings. In contrast, a highly fractured rock mass without dominant cracks is characterized by an S-wave velocity gradient with shear-wave velocity being significantly reduced close to the surface. Generally, normal modes do not develop, but surface waves propagate in such structures, which can be used for the determination of the S-wave profile. This is typical for large deep seated landslides with a layered structure. Without strong S-wave velocity contrast at depth, H/V spectral ratios show no clear peak and are not conclusive to characterize structures with highly fractured material. However, frequency-dependent ground-motion amplification from standard spectral ratios is directly related to the S-wave velocity profile and damping. Therefore, wave amplification can be a measure for the disintegration of the rock.&lt;/p&gt;&lt;p&gt;Repeated measurements on slopes allow for the detection of possible changes in their properties. Semi-permanent installations on instabilities of interest allow for a continuous assessment of the dynamic response in order to understand variations due to weather conditions and potential long-term changes. This includes the measurement of site-amplification during earthquakes derived from empirical spectral modelling. When measuring in the same season and weather condition, the seismic response of rock instabilities in general remains unchanged over years, as long a no external trigger affects the instability, including a strong earthquake, partial failure of the slope or permafrost degradation.&lt;/p&gt;

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