Civil Engineering Reference
In-Depth Information
rently based only on PAGER's empirical loss models. It was recognized that
for some regions where numerous and frequent damaging earthquakes
have occurred in the recent past, the empirical fatality and economic loss
estimation models can be used for quickly assessing the overall impact for
operational response purposes (Wald
et al.
, 2008a). The semi-empirical and
analytical loss estimation models implemented within the PAGER system
require building inventory, vulnerability, and economic exposure datasets
at the country level. These models can provide approximate damage and
loss estimates only in regions where the requisite-quality data and models
are available. The following subsections describe each of these models,
though for brevity the reader is referred to relevant literature for additional
details.
31.4.1 Empirical model
Empirical modeling has been performed in a variety of ways depending
upon the earthquake damage data available. Researchers in Japan attempted
casualty estimation as early as the 1950s. Kawasumi (1951) developed a
measure of earthquake hazard and expectation of maximum intensity in
Japan. Similarly, early casualty estimation efforts in the United States were
scenario specifi c and based on estimation of the casualty rate per 100 000
people and use of engineering judgment (Algermissen
et al.
, 1972). Ohta
et
al.
(1983) developed an empirical relationship for estimating the number
of casualties as a function of the number of completely destroyed houses.
Oike (1991) proposed a relationship between earthquake magnitude and
earthquake fatalities. A log-linear relationship of fatalities as a function of
magnitude and population density was derived by Samardjieva and Badal
(2002) by analyzing 450
global earthquakes. Nichols and Beavers (2003)
studied the fatality catalogue of the twentieth century and established a
bounding function using the fatality count and the USGS-assigned earth-
quake magnitude.
The PAGER empirical model estimates earthquake fatalities or expected
economic losses
E
(
L
) at each level of shaking intensity
s
(typically repre-
sented by MMI). The estimates are based on the exposure (either the total
population exposed, or the total economic exposure, i.e., the monetary
value of all the exposed physical assets) and the
loss ratio
(which can be
fatality rate
v
or economic loss ratio
r
) corresponding to each level of MMI
directly obtained from ShakeMap (http://earthquake.usgs.gov/shakemap/).
Total losses are computed by summing the losses from different intensities
to estimate total losses for a given earthquake
j
:
+
()
=
∑
(
)
×
(
)
EL
j
Exposure
Loss Ratio
[31.1]
sj
,
sj
,
s
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