Probabilistic seismic hazard analysis of civil infrastructure - Seismic Risk Analysis and Management of Civil Infrastructure Systems - page 2

motion levels as a function of probability) and uniform hazard spectra (i.e.
ordinates of expected ground motion levels for a given probability as a
function of vibration period). These are essential tools for developing
national seismic hazard maps and modern seismic design provisions in
national building codes. For instance, the current seismic design codes in
the United States and Canada specify expected ground motion intensities
at 2% probability of exceedance in 50 years (i.e. 2475 years return period
level). The adopted probability level is related to regional seismicity and
historical progress of seismic design requirements (including intended risk
targets) and should be determined by balancing with other social require-
ments, such as health and welfare (Rosenblueth, 1986).
The conventional PSHA is composed of three major modules: (1) earth-
quake occurrence in time and space and earthquake source characteristics,
(2) ground motion prediction (including path and site effects), and (3)
integration of hazard contributions and treatment of uncertainties. An illus-
tration of a typical PSHA procedure (and its extension to conduct more
advanced analyses, as described below) is shown in Fig. 1.1. The spatiotem-
poral earthquake occurrence is often characterised by fault/areal seismic
sources. The delineated sources refl ect past seismic activities in a region
(historical and instrumental earthquake catalogue), and their activity rates
can be determined based on a slip rate for a fault segment, and/or charac-
terised by a magnitude-recurrence relationship for an areal zone. As the
fi rst module of PSHA, a synthetic regional seismic catalogue can be gener-
ated using Monte Carlo simulation (Musson, 2000; Hong et al. , 2006). The
second module evaluates seismic intensity measures at a site of interest for
all signifi cant earthquake scenarios (generated by the fi rst module), typi-
cally by using a ground motion prediction equation (GMPE). Internally
consistent magnitude and distance measures should be considered in evalu-
ating the ground motions expected at the site (Scherbaum et al. , 2004;
Bommer et al. , 2005). Random scatter of motions about the median GMPE
must be incorporated in the assessment. Alternatively, more extensive
approaches based on stochastic simulation methods can be adopted (Wen
and Wu, 2001). Although the implementation of modules 1 and 2 captures
some uncertainties, a more comprehensive consideration of possible alter-
natives is needed. Such alternatives include: different source characterisa-
tions/zones (e.g. kernel smoothing and tessellation; Woo, 1996; Beauval et
al. , 2006; Hong et al. , 2006), time-dependent seismic hazard (e.g. renewal
model; Goda and Hong, 2006), uncertainties associated with magnitude-
recurrence relationships (e.g. parametric uncertainties and bias due to com-
pleteness and magnitude-scale inhomogeneity; Weichert, 1980; Atkinson
and McCartney, 2005), and choice of multiple regional GMPEs (e.g. selec-
tion of suitable equations and their weighting in a logic tree; Bommer
et al. , 2005). The above-mentioned issues have been already addressed and