Publication Date:
2017-04-04
Description:
A large data set of ground-velocity time histories from earthquakes that
occurred in Friuli-Venezia Giulia (northeastern Italy) was used to define regional
predictive relationships for ground motion, in the 0.25- to 14.0-Hz frequency band.
The bulk of the data set was provided by the seismic network run by Centro Ricerche
Sismologiche (CRS), a department of the Istituto Nazionale di Oceanografia e Geofisica
(OGS). A collection of 17,238 selected recordings from 1753 earthquakes was
compiled for the years 1995–1998, with magnitudes ranging from Mw !1 to 5.6.
Ninety-six three-component strong-motion waveforms belonging to the largest
events of the 1976–1977 Friuli seismic sequence were also taken from the ENEAENEL
accelerogram database and included in our data set. For the strongest event,
which occurred on 6 May 1976 at 20:00 local time, an average local magnitude ML
6.6 was computed by Bonamassa and Rovelli (1986). The inclusion of a large number
of acceleration time histories from this earthquake and six others, from magnitudes
from Mw 5.2 to magnitude Ms 6.1 (three of them of Ms !6.0), extends the validity
of the predictive relationships proposed in this study up to the highest magnitude
ever recorded in the region.
A total of 10,256 vertical-component and 6982 horizontal-component seismograms
were simultaneously regressed for excitation and site characteristics, as well
as for the crustal propagation, in the hypocentral distance range 20–200 km. Results
are given in terms of excitation, attenuation, and specific site for the vertical ground
motion, together with a horizontal-to-vertical ratio for each existing horizontalcomponent
seismometer. The regional propagation was modeled in the 0.5- to 14.0-
Hz frequency band by using a frequency-dependent piece wise continuous linear (in
a log–log space) geometrical spreading function and a frequency-dependent attenuation
parameter:
Q( f ) ! 260( f /1.0)0.55
The excitation spectra of larger events were modeled by using the regional propagation,
a single-corner frequency Brune spectral model characterized by an effective
stress parameter,
Dr ! 60 MPa,
and by a regional estimate of the near-surface, distance-independent, networkaveraged
attenuation parameter
j0 ! 0.045 sec
that was estimated from the rolloff of the empirical source spectra obtained from the
regressions. Other studies (De Natale et al., 1987; Cocco and Rovelli, 1989; Singh
et al., 2001) suggested large stress drops (Dr ! 30–100 MPa,) to explain the highfrequency
amplitude levels of the seismic radiation of the largest quakes of the 1976
sequence.
Predictions for peak ground acceleration (PGA) and pseudo–spectral velocity
(PSV) (5% damping) were computed through the use of the random vibration theory
(RVT), with the parameters obtained from the regressions of this study.
Description:
This study was
supported by the Gruppo Nazionale Difesa dai Terremoti, (GNDT) through
the project Terremoti probabili in Italia tra l’anno 2000 e il 2030: elementi
per la definizione di priorita` degli interventi di riduzione del rischio sismico,
task 3.1. The contribution of R. B. Herrmann was supported in part by the
Earthquake Engineering Research Center’s Program of the National Science
Foundation under Award No. EEC-9701785.
Description:
Published
Description:
2186-2204
Description:
4.1. Metodologie sismologiche per l'ingegneria sismica
Description:
JCR Journal
Description:
reserved
Keywords:
Attenuation law
;
peak ground acceleration
;
pseudo-spectral velocity
;
04. Solid Earth::04.06. Seismology::04.06.04. Ground motion
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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