Civil Engineering Reference
In-Depth Information
The rationale for this dual approach to earthquake alerting stems from
the recognition that relatively high fatalities, injuries, and homelessness
dominate in countries where local building practices typically lend them-
selves to high collapse and casualty rates. It is these impacts that drive
prioritization for international response. In contrast, it is often fi nancial and
overall societal impacts that trigger the level of response in regions or
countries where prevalent earthquake resistant construction practices
greatly have reduced building collapse and resulting fatalities. Since PAGER
calculations are available well in advance of ground-truth observations or
news accounts, PAGER information can play a primary alerting role for
domestic as well as international earthquake disasters. For US events, the
trigger threshold is lower than the global magnitude trigger, with Shake-
Maps produced for magnitude 3.5 to 4.5 depending on the region.
An example of the PAGER summary product, or
onePAGER
, is pre-
sented in
Plate VI
(between pages 452 and 453). This summary page shows
the earthquake impact alert produced by operational PAGER system
within minutes following the
M
w
9.0 Tohoku earthquake in Japan indicating
a red alert for economic losses (median, i.e., 50 percentile economic loss
value from shaking-only causes exceeding 8.0 billion USD). The PAGER
alert indicated that there was a likelihood of hundreds of shaking-related
fatalities and that economic losses induced from shaking-related damage
could be widespread, and thus the event would require national or interna-
tional level response based on historical precedence. Note that the losses
estimated by the PAGER system are from shaking-related causes only, and
thus it does not account losses caused due to landslide, liquefaction, tsunami,
or fi res following earthquakes. According to recent estimates, this earth-
quake caused at least 15867 (NPAJ, 2012) deaths, mainly from tsunami-
related causes, with a much smaller fraction of total deaths, in the hundreds,
due to shaking-related causes. Similarly, this event caused an enormous
economic impact of the order of 235 billion (
Los Angeles Times
, 2012), of
which at least 77 billion (Khazai
et al.
, 2011) might have been attributed
due to shaking-related causes.
When the two individual alert estimates differ, the higher alert level is
automatically chosen by the PAGER system. Each individual alert level is
based on the expected value of loss; uncertainty in the alert level can be
gauged by the histogram showing the percentage likelihood that adjacent
alert levels (or loss/fatality ranges) occur. Accompanying text clarifi es the
nature of the alert based on experience from past earthquakes and provides
context on the total economic losses in terms of the percent of the GDP of
the country affected. Not all the uncertainties are incorporated while deter-
mining the earthquake fatalities and associated economic losses, and hence
the actual impact of the earthquake may be different from the automati-
cally generated PAGER alert estimates.
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