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effective duration. The spectra for rocky foundations (
Vs
>800 m/s) should be
compared to those coming from 293 Japanese recordings on 91 dam sites, from 63
earthquakes of magnitude higher than 5 [MAT 03]. Two types of events are
distinguished: superficial, deep or interface failure. They take the general form:
Lod
SA
(T) =
Cm
(T)*M +
Ch
(T)*H −
Cd
(T)*log(R + 0.334exp(0.653M)) +
Co
(T)
with
SA
being horizontal pseudo-acceleration,
T
period,
M
magnitude JMA (Japan
Meteorological Agency),
H
focal depth limited to 100 km, and
R
minimum distance
to the fault.
For
T
= 0, we obtain the acceleration of null period PGA (Peak Ground
Acceleration)
.
The coefficients are given by bi-linear relations with the logarithm of the period
connecting three particular points corresponding to the periods T1 = .01 s, T2 = .2 s,
T3 = 4 s (Table 10.2).
Coefficient
T1 = 0.01 s
T2 = 0.2 s
T3 = 4.0 s
Cm
0.54
0.54
0.85
Ch
0.0054
0.0054
0.002
Co
1.25
1.25
-2.5
Cd
1.75
1.75
1.25
Table 10.2.
Spectrum coefficients [MAT 03]
10.4.4.2.
Energetic method
Experience has shown that if we apply the same acceleration to two earthquakes,
one close by and one far away, the more destructive one will be the farther one. This
result shows that it is not enough to characterize seismic hazard by the maximum
acceleration factor. It also implies that there is an unknown law for seismic energy
propagation. Knowing what this propagation law is would allow us to replace the
couple spectrum and maximum acceleration by a sole parameter representing
seismic hazard.
Nowadays, two characteristic factors are studied: Arias and Housner intensities.
Recent studies [BRU 03] have shown that the Arias intensity is well correlated to the
maximum displacements of the embankment dams, whereas the Housner intensity is
well correlated to the maximum deformations at depth. The correlation is better if
the earthquake duration is also taken into account. Current studies have tried to
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