
 DOESTD102395
= 4.6, consistent with the lower bound used for national seismic hazard maps, e.g. BSSC
(1988).
The hazard model is developed by examining characteristics of seismic sources and their
contribution to the seismic hazard of the site (Cornell 1968). For a detailed description of
acceptable methodologies, see SSHAC (1997).
The following discussion summarizes the four standard steps in the methodologies.
Step 1:
A zonation map is developed (with possibly additional information on the spatial
distribution of earthquakes in any given zone). The zonation is a partition of the
entire area of interest into independent seismic source zones. Each zone is
assumed to be a unique source of earthquakes and to have its own recurrence
distribution. A zone can be described by an area or a fault (such as for western
U. S. Sites).
Step 2:
The recurrence (frequencymagnitude distribution) is defined for each zone. This
step quantifies the total number of earthquakes greater than magnitude Mo
expected to occur during the period of interest (usually one year), and it
describes the relative frequency of all the magnitudes greater than Mo. An
upper bound (maximum) magnitude is defined for each recurrence distribution.
Step 3:
The ground motion model provides the probability that g is exceeded at the site
(at a hypothetical rock outcrop) when an earthquake of magnitude m has
occurred at a given location. Usually, the direction of the origin of the
earthquake is neglected and only the distance r to the site is considered in the
ground motion modeling:
P (G g, for given m and r).
The measure of the sourcetosite distance may vary depending upon the
procedure used to estimate earthquake attenuation effects.
For a site where the ground motion model is not specifically applicable to the
local geology, a site response evaluation should be completed. The site response
evaluation should consider field investigations, sampling, and testing as
described in DOESTD102294.
The site correction should be applied consistent with McGuire, et. al. (2001).
Step 4:
The hazard curve SH(g) is calculated by integrating the effects of all possible
earthquake locations and all possible earthquakes with magnitudes greater than
Mo occurring within all seismic source zones. The seismic hazard curve
expresses the annual frequency of exceeding particular ground motion levels.
A2

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