Publication Date:
2018-03-23
Description:
Amplitudes and frequency content of the seismic ground motion
generated by an earthquake and recorded at a specific location depends
on the characteristics of the source, the path from the source
to the site and the local geologic conditions. The local site seismic
response is produced by multiple physical phenomena (i.e., reflection,
diffraction, focusing, resonance effects, non-linear soil
behavior) that can amplify or decrease amplitudes of seismic waves
near to the surface causing high variability in the observed ground
motions. In particular, vertical discontinuities and abrupt changes
in the velocity profile, or lateral heterogeneities such as faults
and/or stratigraphic contacts can have a strong impact. A correct
and quantitative assessment of site effects is required for both the
interpretation of observed waveforms and the reliable prediction
of resultant ground motions (e.g., computation of specific earthquake
scenarios). In addition, the extent and distribution of building
damage due to moderate and large earthquakes in densely
populated areas are a result of the combined effect of local site
response and the dynamic properties of man-made structures.
The quantification of ground motion amplification are therefore
of primary interest for seismologists and engineers in order to
reduce associated risks.
Recent advances in engineering seismology research resulted in
improvements in the study of seismic site response both from the
theoretical and experimental points of view. For example, new numerical
modelling techniques have become available, which account
for non-linear soil behavior. Growing seismic networks
allow for the more advanced site response estimates compared to
the past as well (e.g. the development of more reliable ground motion
prediction equations).
This thematic issue focuses on local seismic site effects and represents
a collection of research papers and case studies on the effect
of subsurface structure on ground motion from new observations,
numerical modelling, as well as geophysical imaging. This volume
also includes contributions related to the Earth system response
to earthquake processes.
In the first paper of this volume, Germoso et al. (2017) analyse
the effects of fractional derivatives in visco-elastic dynamics for
site response analysis. They prove that the use of fractional derivatives
for representing the viscous terms offers a larger flexibility in
the resulting models (compared to standard methods), and allow
them to better quantify the degree of dissipation as well as the
magnitude of deformation and phase angle. Poggi et al. (2017) present
three different soil amplification models for 5% damped
pseudo-spectral acceleration response spectra using recordings of
88 selected stations of the Japanese KiKNet strong-motion network.
While they do not provide a ranking of the applied methods, they
evaluate the strengths and weaknesses of the each tested technique.
Michel et al. (2017) present a site amplification study for
the city of Basel (Switzerland), by combining data achieved using
geophysical site characterization and site response modelling.
They obtain amplification maps of the response spectrum at
different periods for earthquake engineering and maps for implementation
in ShakeMap. Pischiutta et al. (2017) perform geophysical
investigations in the northwestern sector of the island of
Malta to reconstruct velocity-depth models by using active and
passive methods. They observe ground motion amplification at
rock sites, highlighting the importance of performing velocity measurements
even for such sites. In fact, using only a lithological criterion
and following the EuroCode EC8, rock sites would be
associated to class “A” where no amplification is expected.
Hayashi and Craig (2017) measure S-wave velocity profiles at
eleven sites in the Eastern San Francisco Bay area using surface
wave methods. A S-wave velocity cross section which runs perpendicular
to the Hayward fault is derived and the theoretical site
amplification is calculated using a viscoelastic finite-difference
method. Their results show that ground motion is amplified on
the west side of the Hayward fault as an effect of the lateral variations
of the S-wave velocity. Panzera et al. (2017) investigate the
characteristics of the local seismic response in Lampedusa (Italy),
a carbonate shelf belonging to the foreland domain at the northern
edge of the African plate. Ninety-two ambient noise recordings
were collected and processed through spectral ratio techniques.
Their results point out the importance of seismic site effects by
the presence of both morphologic and tectonic structures. Moisidi
(2017) examine the potential soil-building resonance at selected
buildings in a complex geological setting of the small scale Paleohora
Basin (southwest Crete). This study highlights the necessity
of incorporating the determination of potential coupling effects between
site and buildings into urban planning for risk mitigation
studies. Di Naccio et al. (2017) present an interdisciplinary
approach to investigate the seismic response of the San Gregorio
(L'Aquila, Italy), a rock site severely damaged by L'Aquila 2009
earthquake. Based on geological-structural, geophysical and
seismic analyses, their results highlight the role of rock mass fracturing
on seismic amplification, that generates lateral variations
in seismic velocity. Bonilla et al. (2017) apply seismic interferometry
to compute the in-situ shear wave velocity to evaluate the
seismic response of sediments. They conclude that their approach
is a robust method to extract shear wave velocity profiles and evaluate
non-linear soil response. A seismic characterization of the flat
Contents lists available at ScienceDirect
Physics and Chemistry of the Earth
journal homepage: www.elsevier.com/locate/pce
Physics and Chemistry of the Earth 98 (2017) 1e2
http://dx.doi.org/10.1016/j.pce.2017.04.005
1474-7065/© 2017 Published by Elsevier Ltd.
top area of Monteluco (Italy) carbonate mountain using a multidisciplinary
approach was performed by Durante et al. (2017). They
hypothesize that local seismic amplification is related to topography
and to an intensely fractured shallow-seated formation
with relatively low shear wave velocity. Pazzi et al. (2017) investigated
the Castagnola (La Spezia, Italy) and Roccalbegna (Grosseto,
Italy) landslides through ambient vibrations. They estimated horizontal
to vertical spectral ratio on a dense grid of points and obtained
useful information on the main impedance contrast depths
for large areas. The interpolation of the obtained fundamental frequencies
enables the detection and reconstruction of the landslides'
slip surfaces. The thematic issue is closed by the papers of
Bogdanov et al. (2017) and Pierotti et al. (2017) that present the
physical and chemical anomalies in the local environment before
and after an earthquake.
Description:
Published
Description:
1-2
Description:
4T. Sismologia, geofisica e geologia per l'ingegneria sismica
Description:
JCR Journal
Keywords:
Site amplification, Malta
;
04.06. Seismology
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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