Characteristics of strong ground motion data recorded in the Gubbio sedimentary basin (Central Italy) |
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| Authors: | F Pacor D Bindi L Luzi S Parolai S Marzorati G Monachesi |
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| Institution: | (1) Istituto Nazionale di Geofisica e Vulcanologia, Via Bassini 15, 20133 Milano, Italy;(2) GeoForschungsZentrum Potsdam, Telegrafenberg, 14473 Potsdam, Germany;(3) Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, 00143 Roma, Italy |
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| Abstract: | Various authors, analysing the set of accelerograms recorded at Gubbio Piana (GBP) (central Italy), have demonstrated that
strong amplification occurs at this accelerometric station, which is installed within an alluvial basin. In particular, Ambraseys
et al. (2005a), Bull Earthq Eng 3:1–53; (2005b), Bull Earth Eng 3:55–73] observed that the strong motion peaks at GBP greatly
exceed the median values predicted by the attenuation relationships they derived for Europe. In this work, we analyse and
discuss some characteristics of the ground motion recorded at the GBP station. We show that the ground motion parameters,
such as peak-ground acceleration and peak-ground velocity, are strongly influenced by the presence of locally induced surface
waves that produce both a lengthening of the significant shaking duration and an increase in the peak values with respect
to a nearby bedrock site. The basin-induced surface waves are observed in the three components of motion and their effects
on the peak values are particularly evident in the vertical component. In the frequency domain, the energy of the surface
waves is mostly restricted to the frequency band 0.4–0.8 Hz for both the horizontal and vertical components. The horizontal
and vertical Fourier amplitudes are also very similar, and this indicates that the H/V spectral ratio technique is not applicable
to describing the site response due to the propagation of seismic wave in a complex 2D/3D geological structure. Finally, a
preliminary polarization analysis shows that the directions of polarization, as well as the degree of elliptical polarization,
exhibit a strong variability with time, that may be related to a complex propagation of Love and Rayleigh waves within the
basin. |
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| Keywords: | Strong motion Alluvial basin effects Site effects Gubbio plain |
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