Diapositiva 1

1


wp 4 Real -Time Shake Maps GRSmap a tool for
rapid estimation of ground-shaking maps for
seismic emergency management in the Campania
Region of southern Italy Convertito V.1, De
Matteis R.2, Cantore L.3, Caccavale M.4, Zollo
A.4 and Iannaccone G.1 1Istituto Nazionale di
Geofisica e Vulcanologia, Osservatorio Vesuviano,
Napoli 2Dipartimento di Studi Geologici ed
Ambientali Università degli Studi del Sannio,
Benevento 3AMRA scarl, Napoli 4Dipartimento di
Scienze Fisiche, Università degli Studi di Napoli
Federico II
Final Meeting Potsdam, 3-5 June 2009
Introduction In the present study, we illustrate
a technique, named GRSmap, for rapid computation
of ground-shaking maps after moderate-to-large
earthquakes. It takes advantage of the high
density of the Irpinia Seismic Network (ISNet)
seismic stations and their wide dynamic ability
to provide non-saturated, ground-motion
measurements. The technique is based on an
optimal data gridding scheme that uses
triangulation, where the recording stations are
the vertices of the triangles, aimed at
reproducing the bi-dimensional feature of the
ground-motion field due to focal mechanism,
directivity etc.. The technique has been applied
at two earthquakes a simulated M 6.6 earthquake
and the 23 November 1980 (M 6.9) earthquake. The
results are finally validated by using a
bootstrap like test while excluding an increasing
number of stations (6, 10 and 14 stations) from
the input dataset and re-computing the maps.
Next, given the new maps, the peak ground
acceleration and peak ground velocity data at
points corresponding to the excluded stations
were extrapolated from the maps and compared with
the original input data. Geological
macrozonation of the southern Apennines To allow
for site amplification effects in the predicted
ground-shaking maps following the approach
proposed by Park and Ellrick (1998), a geological
macro-zoning of the southern Apennines region was
performed (Fig.1). The main geological units have
been grouped based on age similarity, following
the Quaternary-Volcanic-Tertiary-Mesozoic (QVTM)
classification (Cantore et al., 2008). The
corresponding corrective coefficients are those
reported by Wald et al. (1999a), except for the
volcanic lithology, for which a preliminary value
of 1.25 has been assumed, based on geological
information (Cantore et al., 2008).

• Methodology outline for computation of the
  ground-shaking maps
• The outline of the GRSMap methodology can be
  schematically summarized as follows
• Triangulation of the data domain
• The recorded peak values are reduced to
  rock-site conditions by using the QVTM
  classification. The seismic stations are
  triangulated and the barycentre are identified
  and used as the phantom seismic stations.
• The maximum acceptable area of each triangle
  cannot exceed NA?Aave, where NA is an integer
  that depends on the seismic network
  configuration, and Aave is the average area of
  all of the triangles.
• Areas exceeding a fixed threshold, are
  recursively triangulated and the new barycentres
  used as additional vertices. When the area is
  lower than the selected threshold value, at all
  of the new barycentres Pga and Pgv will be
  assigned using the equation (1) corrected by the
  average residual calculated on a fixed number of
  real seismic stations.
• The epicentre is considered as an additional
  station where the datum is estimated by equation
  (1) for R0 km and corrected by an average
  residual, computed at a number of stations
  surrounding the epicentre below a distance value
  that depends on seismic network density.
• For an earthquake located outside of the data
  domain area, triangulation of the epicentral area
  is made denser and denser until a uniform station
  distribution is obtained.

Figure 3 (a) The main parameters of the
triangulation scheme. Black triangles represent
seismic stations, black circles the barycentres,
and open circles the virtual stations (phantom
stations). (b) The triangulation for ISNet. (c)
The triangulation for the network at which the
1980 Irpinia earthquake (M 6.9) was recorded.
Extrapolation of peak motion in the external area
The external area is covered with a uniform grid
of phantom stations (Fig. 3a). Only those nodes
of the grid located at distances larger than the
threshold value from the closest recording
station are retained for the extrapolation (Fig.
3a). At each retained node, Pga and Pgv are then
predicted using equation (1), adding a mean
residual weighted for the epicentral distance,
computed at seismic stations with an azimuth with
respect to the epicentre, comparable with that of
the considered phantom station. Estimated and
recorded data are then integrated onto 0.01
degree spaced map. Applications and
resultsvalidation The technique GRSMap has been
applied to two earthquakes a simulated M 6.6
seismic event with data computed at the ISNet
stations (left panels of Fig.4), and the 23
November 1980 Irpinia earthquake (M 6.9) recorded
at a local seismic network (right panels of
Fig.4)..
Figure 1The QVTM site geological classification
map. The labels indicate the locations of the
ISNet seismic stations.
Ground-motion prediction in the southern
Apennines To limit the effects of using
attenuation relationships retrieved from dataset
recorded in a different region, for the
Campania-Lucania Region, Convertito et al. (2007)
developed an ad-hoc regional ground-motion-attenua
tion relationship for the prediction of peak
ground acceleration (Pga) and velocity (Pgv)
values for moderate-to-large earthquakes. The
coefficients were retrieved from an integrated
observed and synthetic strong-motion database
that was obtained using the stochastic approach
proposed by Boore (1983). The selected prediction
model has the following formulation
Where R corresponds to the epicentral distance in
km, h is a fictious depth in km. The retrieved
coefficients for both Pga and Pgv are listed in
Table 3.
Table 3 Regression coefficients and standard
errors of the regional attenuation relationship
used to compute the ground-shaking maps.
Asterisks indicate the coefficients of the same
attenuation relationships obtained without
introducing the Pga and Pgv values of the 23
November 1980 Irpinia earthquake into the dataset.
Figure 5 Results of the bootstrap test. The
squares correspond to the residuals when the
estimated data are retrieved from the maps using
the interpolation procedure, while the gray
circles correspond to the residuals obtained when
the attenuation relationships are used to
estimate the Pga and Pgv values.
Figure 4 Ground shaking maps.

• References
• - Boore D.M. (9183). Stochastic simulation of
  high-frequency ground motion based on
  seismological models of the radiated spectra,
  Bull Seism Soc Am 731865-1893
• - Cantore L (2008). Determination of site
  amplification in the Campania-Lucania region
  (Southern Italy) by comparison of different
  site-response
• estimation techniques, Ph. D. Thesis, Dip. di
  Fisica, Università Federico II di Napoli
• Cantore L., ConvertitoV., Zollo A. (2009).
  Development of a site conditions map for the
  Campania-Lucania region (Southern Apennines,
  Italy). Submitted to BEE
• Convertito V., De Matteis R., Cantore L., Zollo
  A., Iannaccone G., Caccavale M. (2009). Rapid
  estimation of ground-shaking maps for seismic
  emergency management in the Campania Region of
  southern Italy. Natural hazards,, doi
  10.1007/s11069-009-9359-2
• Convertito V., De Matteis R., Romeo A., Zollo
  A., Iannaccone G. (2007) Strong motion relation
  for early-warning applications in the Campania
  Region (southern Apennines), Italy. In Gasparini
  et al (eds) Earthquake early warning systems,
  Berlino, Springer-Verlag
• Wald D.J., Quitoriano V., Heaton T.H., Kanamori
  H., Scrivner C.W., Worden C.B. (1999a) TriNet
  shakemaps rapid generation of instrumental
  ground motion and intensity maps for earthquakes
  in southern California, Earthquake Spectra
  15537-555

Figure 2 Validation of synthetic Pga (a) and Pgv
(b) relative to the M 6.6 earthquake values. On
each panel, the crosses represent the Pga and
Pgv values retrieved from the synthetic
waveforms simulated at the ISNet recording
stations. Black lines on panels a and b refer to
the median values of the Convertito et al. (2007)
attenuation relationships, while dashed lines
refer to ?1?. Panel c shows the same data when
the minimum fault distance (Rjb) is taken into
account. Black lines refer to Sabetta and
Pugliese (1996) attenuation relationship, while
grey lines refer to Akkar and Bommer (2007)
attenuation relationship.