Publication Date:
2017-04-04
Description:
Abstract Several different attenuation models have recently been proposed for the
Italian region to characterize the decay of macroseismic intensity with the distance
from the source. The significant scatter between these relationships and some significant
drawbacks that seem to characterize previous approaches (described in a companion
article by Pasolini et al., 2008) suggest that the problem needs to be
reconsidered. As a first step toward more detailed analyses in the future, this study
aimed at developing an isotropic attenuation relationship for the Italian area. Because
this attenuation relationship has to be used primarily in probabilistic seismic hazard
assessment, major attention was given to evaluating the attenuation relationship in its
complete probabilistic form. Another important aspect of this study was the preliminary
evaluation of the intrinsic (i.e., independent of the specific attenuation relationship
to be used) scattering of data, which represents the lowest threshold for the
residual variance that cannot be explained by the attenuation relationship. Furthermore,
the peculiar formal features of intensity data and relevant uncertainties were
considered carefully. To reduce possible biases, the completeness of the available
database was checked and a suitable data selection procedure was applied. Since epicentral
intensity cannot be defined unambiguously from the experimental point of
view, the attenuation relationship was scaled with a new variable that is more representative
of the earthquake dimension. Several criteria were considered when evaluating
competing attenuation formulas (explained variance, Bayesian information
criteria, Akaike information criteria, etc.). Statistical uncertainty about empirical parameters
was evaluated by using standard approaches and bootstrap simulations. The
performance of the selected relationship with respect to a control sample was analyzed
by using a distribution-free approach. The resulting equation for the expected intensity
I at a site located at epicentral distance R is
I IE 0:0086 0:0005 D h 1:037 0:027 ln D ln h ;
where D
R2 p h2, h 3:91 0:27 km, and IE is the average expected intensity
at the epicenter for a given earthquake that can be computed from the intensity
data (when available) or by using empirical relationships with the moment magnitude
Mw or the epicentral intensity I0 reported by the Italian seismic catalog
IE 5:862 0:301 2:460 0:055 Mw;
IE 0:893 0:254 1:118 0:033 I0:
Comparison of the model standard deviation (S.D.) (0.69 intensity degrees) with the
intrinsic one (0.62) indicates that this attenuation equation is not far from being
optimal.
Description:
Published
Description:
692-708
Description:
JCR Journal
Description:
reserved
Keywords:
Macroseismic intensity, Ground motion prediction equation
;
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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