Publication Date:
2017-04-04
Description:
The city of Palermo is an appropriate test site where the efficiency of microtremors in predicting ground
motion properties during earthquakes can be checked. Palermo is a densely populated city with important
historical heritage and was object of previous studies. Areas of local amplification of damage were identified
in downtown Palermo using historical macroseismic data. Moreover, aftershocks of the September 6, 2002,
earthquake (Mw 5.9, 40 km offshore) provided a dataset of seismograms that quantify spatial variations of
ground motion. The availability of more than 2000 boreholes in the city allowed a reconstruction of the 3D
structure of surface geology, indicating that all the higher damage zones correspond to sediment-filled
valleys. The high variability of the surface geology is mostly due to the presence of two filled river-beds of
about 150 m width. In the framework of the SESAME project (Seismic EffectS assessment using Ambient
Exctations, funded by the European Union), 90 microtremor measurements were performed across several
profiles crossing the soft sediment bodies. The measurement points were intensified close to the valley edges
(every 20 m), according to our geological reconstruction. H/V spectral ratio on ambient noise (HVSR) show
significant variations along each profile: as soon as the transition stiff to soft is crossed, a typical spectral
peak exceeding a factor of 3 in amplitude appears in the HVSR. The peak falls between 1 and 2 Hz and,
along each profile, the peak disappears as soon as the other edge of the valley is crossed. These results
indicate that microtremors are sensitive to the presence of large impedance contrasts of deep soft soil, at least
in the Palermo area, with an important implication: the HVSR method seems to be able to recognize
conditions potentially favourable to the occurrence of higher damage even when local geological characters
are masked by the urban growth. However, we were not able to establish a quantitative correlation between
microtremor properties and ground motion (or damage) amplification.
Description:
Published
Description:
Vancouver, B.C., Canada
Description:
4.1. Metodologie sismologiche per l'ingegneria sismica
Description:
open
Keywords:
Palermo, noise measurements, macroseismic intensity, ground motion
;
04. Solid Earth::04.06. Seismology::04.06.04. Ground motion
;
04. Solid Earth::04.06. Seismology::04.06.06. Surveys, measurements, and monitoring
;
04. Solid Earth::04.06. Seismology::04.06.09. Waves and wave analysis
;
04. Solid Earth::04.06. Seismology::04.06.11. Seismic risk
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
Conference paper
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