Publication Date:
2023-02-22
Description:
In this paper, we present the work carried out to characterize the spatial variability of
seismic site response related to local soil conditions in the city of Milan and its
surroundings, an area with ~3 million inhabitants and a high density of industrial
facilities. The area is located at the northwestern end of the Po Plain, a large and deep
sedimentary basin in northern Italy. An urban-scale seismo-stratigraphic model is
developed based on new passive and active seismic data, supported by the available
geological data and stratigraphic information from shallow and deep vertical wells. In
particular, 33 single-station and 4 ambient-vibration array measurements are acquired,
together with 4 active multichannel analyses of surface waves (MAWS). To estimate the
resonant frequencies of the sediments, the horizontal to vertical spectral ratio technique
(HVSR) is applied to the ambient-vibration recordings, whereas to determine the Rayleighwave
dispersion curves from the passive array, the data are analysed using the
conventional frequency-wavenumber, the modified spatial autocorrelation and the
extended spatial autocorrelation (ESAC) techniques. The array data are used to
determine the local shear wave velocity profiles, VS, via joint inversion of the Rayleighwave
dispersion and ellipticity curves deduced from the HVSR. The results from HVSR
show three main bands of amplified frequencies, the first in the range 0.17–0.23 Hz, the
second from 0.45 to 0.65 Hz and the third from 3 to 8 Hz. A decreasing trend of the main
peaks is observed from the northern to the southern part of the city, allowing us to
hypothesize a progressive deepening of the relative regional chrono-stratigraphic
unconformities. The passive ambient noise array and MASW highlight the dispersion of
the fundamental mode of the Rayleigh-wave in the range 0.4–30 Hz, enabling to obtain
detailed Vs. profiles with depth down to about 1.8 km. The seismo-stratigraphic model is
used as input for 1D numerical modelling assuming linear soil conditions. The theoretical
1D transfer functions are compared to the HVSR curves evaluated from both ambient
noise signals and earthquake waveforms recorded by the IV. MILN station in the last
10 years.
Description:
Published
Description:
915083
Description:
5T. Sismologia, geofisica e geologia per l'ingegneria sismica
Description:
JCR Journal
Keywords:
milan (Italy), seismic site characterisation, seismostratigrahic model, vs. velocity profile, seismic array, MASW, HVSR (horizontal to vertical spectral ratio), 1D numerical modeling
;
Solid Earth
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
