Publication Date:
2017-04-04
Description:
During the MW 5.7 and 6.0 Umbria–Marche earthquakes of 1997 September 26, the historical
centre of Nocera Umbra suffered MCS intensity VII–VIII. The zone is located on the top
of a hill, a condition potentially favourable to ground motion amplification. However, also
vulnerability is higher on the hill because of the ancient age of buildings. A temporary array
of eight seismological stations was installed across the hill to quantify the amplification effect
due to topography.Waveforms of 14 aftershocks (2.6〈ML 〈4.1) are selected for the analysis.
During each earthquake the largest amplitudes are observed on the hilltop, spectral ratios are
computed using rotated horizontal components to search for directional effects. Amplifications
are found in two separate frequency bands: one in the range 2–4 Hz, where the increase of
amplitude is moderate (never exceeding a factor of 4) and the polarization is transversal to the
hill major axis; the second above 10 Hz, where amplifications are larger and reach values as
high as 25 Hz. High-frequency polarization varies for different sites and frequencies suggesting
that smaller-scale complexities control the high frequency response. Synthetic seismograms
of 2-D models confirm the occurrence of amplification, although not all details are fit by
numerical simulations and the agreement between observations and models is significant only
in terms of the fundamental resonance frequency, around 3 Hz. In the models, amplifications
are much smaller than the observed ones. We conclude that topography could have been
responsible for a small increase of damage in the hill zone but the most significant role on
damage was played by the locally higher vulnerability.
Description:
Published
Description:
977-987
Description:
4.1. Metodologie sismologiche per l'ingegneria sismica
Description:
JCR Journal
Description:
reserved
Keywords:
Earthquake ground motion
;
Site effects
;
04. Solid Earth::04.06. Seismology::04.06.04. Ground motion
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
