Geoscience Reference
In-Depth Information
where
35. The seismic displacement (
U
in cm) can then be estimated by multi-
plying the normalized seismic displacement value by the median estimates of
k
max
and
D
5
-
95
. The normalized seismic loading and displacement values are estimated at the
median and 16% exceedance levels to develop a range of estimated seismic displace-
ments.
σ
=
0
.
The Bray et al. (1998) seismic slope displacement procedure provides median and stan-
dard deviation estimates of the seismic demand and normalized seismic displacement,
but does so only in an approximate manner to develop a sense of the variability of the
estimateddisplacement.Itislimitedinthatitwasnotdevelopedinarigorousprobabilis-
tic manner. However, Stewart et al. (2003) were able to use this procedure to develop
a probabilistic screening analysis for deciding if detailed project-specific seismic slope
stability investigations are required by the 1990 California Seismic Hazards Mapping
Act. Additionally, the Bray and Rathje (1998) simplified seismic displacement proce-
durewasadoptedintheguidancedocumentbyBlakeetal.(2002)forevaluatingseismic
slope stability in conformance with the “Guidelines for Evaluating and Mitigating Seis-
mic Hazards in California” (CDMG,1997).
As noted previously, the Bray et al. (1998) method is also limited by the decoupled
approximation employed in the seismic response and Newark sliding block calculations.
Although many more ground motions were used than were used by Makdisi and Seed
(1978), with the large number of well-recorded events since 1998, significantly more
ground motions are now available. These shortcomings motivated a more recent study,
which is summarized in thenext section ofthis paper.
5. Bray and Travasarou (2007) simplified seismic displacement procedure
5.1. EARTHQUAKE GROUND MOTIONS
Currently available simplified slope displacement estimation procedures were largely
developed based on a relatively modest number of earthquake recordings or simulations.
This study took advantage of the recently augmented database of earthquake recordings,
which provides the opportunity to characterize better the important influence of ground
motionsontheseismicperformanceofanearth/wasteslope.Asdiscussedpreviously,the
uncertainty in the ground motion characterization is the greatest source of uncertainty in
calculating seismicdisplacements.
The ground motion database used by Bray and Travasarou (2007) to generate
the seismic displacement data comprises available records from shallow crustal
earthquakes that occurred in active plate margins (PEER strong motion database
http://peer.berkeley.edu/smcat/index.html
)
. These records conform to the following
criteria:(1)5
100km,(3)SimplifiedGeotechnicalSitesB,C,or
D(i.e.,rock,softrock/shallowstiffsoil,ordeepstiffsoil,respectively,Rodriguez-Marek
et al., 2001), and (4) frequencies in the range of 0.25 to 10Hz have not been filtered
out. Earthquake records totaling 688 from 41 earthquakes comprise the ground motion
.
5
≤
M
w
≤
7
.
6,(2)
R
≤
