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


Title (Dublin Core)

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

Description (Dublin Core)

<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>

Creator (Dublin Core)

Paula Teves-Costa
Isabel M. Almeida
Isabel Rodrigues
Rita Matildes
Claudia Pinto

Subject (Dublin Core)

Site effects
Geotechnical database
Theoretical transfer functions
Ground motion amplification
Meteorology. Climatology
Geophysics. Cosmic physics

Publisher (Dublin Core)

Istituto Nazionale di Geofisica e Vulcanologia (INGV)

Date (Dublin Core)


Type (Dublin Core)


Identifier (Dublin Core)


Source (Dublin Core)

Annals of Geophysics, Vol 57, Iss 4 (2014)

Language (Dublin Core)


Relation (Dublin Core)

Provenance (Dublin Core)

Journal Licence: CC BY