Geoscience Reference
In-Depth Information
Moreimportantly,takingadvantageofthegreaternumberofrecordedearthquakeground
motionsavailableatthetime,dozensofdissimilarscaledandunmodifiedrecordedearth-
quakerockinputmotionswereusedwith
PGA
srangingfrom0
8
g
.Theirmethod
was calibrated against several case histories of waste fill performance during the 1989
LomaPrietaand1994Northridgeearthquakes,andlatervalidatedagainstobservedearth
fill performance.
.
2
g
to0
.
TheBrayetal.(1998)procedureprovidesamorecomprehensiveassessmentoftheearth-
quake ground motions, seismic loading, and seismic displacement calculations, but it
requires more effort than the Makdisi and Seed (1978) procedure. In the first step, the
ground motion is characterized by estimating the
MHA
,
T
m
, and
D
5
-
95
for outcropping
rockatthesitegiventheassigneddesignmomentmagnitudeanddistancesfortheidenti-
fied key potential seismic sources. The intensity, frequency content, and duration for the
median earthquake ground motion level fordeterministic events areestimatedusingsev-
eral available ground motion parameter empirical relationships (e.g., Figure 14.8). The
rock site condition is used, which is also consistent with the site condition used in the
development of probabilistic ground motion hazard maps. Additionally, a seismic site
response analysis isnot required toestimate the
PGA
at the topof slope.
Forthedeepslidingcase,theinitialfundamentalperiodofthepotentialslidingmass
(
T
s
)
isestimatedasdiscussedpreviously(i.e.,
T
s
≈
4
H
/
V
s
).Withtheratioof
T
s
/
T
m
,thenor-
malizedmaximumseismicloading(i.e.,
,where
MHEA
is the maximum horizontal equivalent acceleration and
NRF
is the nonlinear response
factor) can be estimated with the graph shown in Figure 14.9, or the equation provided
below, when
T
s
/
(
MHEA
)/((
MHA
rock
)(
NRF
))
T
m
>
0
.
5
ln
(
MHEA
/(
MHA
rock
NRF
))
=−
0
.
624
−
0
.
7831 ln
(
T
s
/
T
m
)
±
ε
(14.1)
1
1.0
60
Strike slip
event
50
0.8
40
0.6
0.1
30
0.4
Mw 6.0
Mw 7.0
Mw 8.0
20
0.2
10
0.01
0.0
0
1
10
100
0
20 40 60 80 100
Distance (km)
0 0
40
0
80
100
(a)
(b)
(c)
Distance (km)
Distance (km)
Fig. 14.8. Simplified characterization of earthquake rock motions: (a)intensity—
MHA
for strike-slipfaults(forreverse faults,use1
3
∗
MHA
for
M
w
≥
64
∗
MHA
.
6
.
4 and 1
.
for
M
w
=
.
.
<
M
w
<
.
4) (Abrahamson and Silva,
1997), (b) frequency content—
T
m
(Rathje et al.,2004), and (c) duration—
D
5
-
95
(Abrahamson and Silva, 1996)
6
0, withlinear interpolation for6
0
6
