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Introduction
An earthquake Toss estimate is a description or forecast of the
ejects of future or hypothetical earthquakes. Loss generally encom-
passes deaths and casualties; direct repair costs; damage or functional
loss to communication, transportation, and other lifeline systems;
emergency response and emergency care facilities; the number of
homeless people; and the impact on the economic well-being of the
region. Earthquake Tosses may be estimated to:
structures;
Identify especially hazardous geographical areas;
Identify especially hazardous groups of buildings or other
Aid in the development of emergency response plans;
Evaluate overall economic impact;
. Formulate general strategies for earthquake hazard reduction,
such as land-use plans or building codes, or evaluate the effectiveness
of earthquake programs;
. Support advocacy efforts aimed at establishing priorities and
budgets for earthquake programs;
. Aid in obtaining quick estimates, made during the first hours
following an actual earthquake, of the approximate impact of the
earthquake; and
. Estimate the expected consequences of a predicted earth-
quake.
6
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The estimation of property losses to assess property insurers'
risks has been one of the more common uses of earthquake loss
estimates, but is only lightly addressed in this report because the
emphasis here is on the broader range of public agency uses.
This report focuses on loss est~rnates of the type being funded
by the Federal Emergency Management Agency (FEMA). They are
intended for local and state government use, primarily for disaster
response planning and to aid in the formulation of near- and long-
term strategies for earthquake hazard reduction. This type of large-
scale lom est~rnate study encompasses a city, region, state, or even
the nation, and it looks at more than one type of loss, typically
including life loss or casualties, property loss, and functional loss or
outages of essential services. A number of such studies have been
completed or are under way. Figure 1-1 illustrates the geographic
scope of past or in-progre" large-scale loss studies, while Table 1-1
bets these major studies.
During the 1970s, the National Oceanic and Atmospheric Ad-
m~n~tration (NOAA) and the U.S. Geological Survey (USGS) am
sembled teams of experts, predominantly engineering consultants
and federal government geoscientists, who produced large-scale Toss
studies that set the basic pattern for the scope and methods of others
to follow. The first four were devoted to the metropolitan areas of
San Francisco (AIgermissen et al., 1972), Los Angeles (AIgerm~ssen
et al., 1973), Puget Sound (Hopper et al., 1975), and Salt Lake City
(Rogers et al., 1976~. These are sometimes collectively referred to
as the NOAA-USGS studies. Some of the more recent studies have
been sponsored by FEMA and carried out by consulting firTns.
In response to a National Security Council request for an eval-
uation of potential impacts on the defense industry impacts, FEMA
also initiated a recent large-scale effort aimed at modeling the re-
gional economic effects of a major earthqualre. This effort involved
a study by the Applied Technology Council (ATC) of methods for
preparing an inventory of facilities and for estimating damage and
functional loss. The result was a report, Earthquake Damage Eval-
uation Data for California, known as ATC-13 (Applied Technology
Council, 1985~. FEMA also began m-house efforts and supported
work by consultants to apply these new methods to selected eco-
nom~c sectors and regions.
Differences exist among the techniques employed in these studies,
arming from different levels of earthquake risk In various parts of
the country, different objectives and budgets, and different authoring
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TABLE 1-1 Areas of the United States Where Large-Scale Loss Studies Have
Been Completed or Are In Progress
Area
a
Study
1. San Francisco, California
2. Los Angeles, California
3. Puget Sound, Washington
4. Salt Lake City, Utah
5. Honolulu, Hawaii
6. Central United States
7. Anchorage, Alaska
S. Boston, Massachusetts
9. Charleston, South Carolina
10. Puerto Rico and
Virgin Islands
11. Clinton County, New York
12 San Diego, California
Algermissen et al., 1972; Davis et al.,
1982b; FEMA, 1980; Steinbrugge et al.,
1981; Steinbrugge et al., in progress
Algermissen et al., 1973; Blume et al.,
1978; FEMA, 1980; Steinbrugge et al.,
1981; D avis et al., 1982a; Scawthorn
and Gates, 1983; Degenkolb, 1984;
California Division of Mines and
Geology, in progress
Hopper et al., 1975
Rogers et al., 1976; U.S. Geological
Survey, in progress
Furomoto et al., 1980; Steinbrugge and
Lagorio, 1982
Mann et al., 1974; Liu, 1981; Allen and
Hoshall et al., 1985
Alaska Division of Emergency Services,
1980; URS/Blume, in progress
Whitman et al., 1980; URS/Blume, in
progress
Lindbergh et al., in progress
Geoscience Associates, 1984 and 1985;
Molinelli and Oxman, in progress
Geoscience Associates, in progress
Reichle et al., in progress
-
aNumbers correspond with studies noted in Figure 1-1.
Organizations. Hence, inconsistencies can be found among the results
of the various studies, and no clear guidance exists for conducting
such studies.
FEMA anticipates the need for future loss estimation efforts.
Seeking to encourage studies that are done in a technically sound, ef-
ficient, consistent manner that will satisfy the needs of users, FEMA
asked the National Research Council to provide "evaluations and rec-
ommendations with regard to methodologies which should be used
for earthquake loss estimation by FEMA and state and local govern-
ments in earthquake preparedness and mitigation planning." This
work statement for the counciT's Pane] on Earthquake Loss Esti-
mation Methodology, within the Committee on Earthquake Engi-
neering, required that the applicability of recommended methods be
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nationwide in scope, or that advice be provided for modifying recom-
mended methods to fit regional variations. In addition to reviewing
present methods, FEMA requested recommendations for testing and
further development of methods to produce more accurate and com-
prehensive loss estimates.
The next section of this chapter presents an overview of the
basic method used to carry out a loss estimate. This is followed by a
discussion in Chapter 2 of the purposes and nature of loss estimates as
viewed by potential users, and then by more comprehensive reviews of
the techniques and methods available for completing the several parts
of a loss estimate. Recommendations for research and development
leading to better loss estimates are given in Chapter 9.
Several important points of a general nature must be emphasized:
~ The methods examined in this report rely on averaging dam-
age and losses over a large group of facilities, and hence apply to
groups of facilities and not to individual buildings. There are tech-
niques for examining in detail the seismic resistance of individual
structures, and brief reference will be made to such techniques. How-
ever, any such detailed analysis can be expensive and time consuming
and therefore generally is not feasible as part of a large-scare study.
When methods intended for large numbers of buildings are used to
estimate losses for individual buildings, the results may be m~slead-
~ng.
This report emphasizes large-scale loss estimates, the basic
method and some of the detailed techniques of which are applicable
to other types of studies.
~ No loss estimate prepared today, or in the foreseeable future,
can be completely accurate. There are major gaps in our knowledge,
both as to the time of occurrence, magnitude, and location of future
earthquakes and as to the manner in which the ground and structures
will respond to earthquakes. Any loss estimation inherently involves
significant uncertainties.
. Despite their limitations, loss studies that are properly con-
ducted and used with an understanding of the methods' limitations
can be of great value. These studies have played an important role
in developing earthquake programs throughout the country, and are
an important too! for initiating effective programs in areas where
earthquakes are a significant threat but have received little atten-
tion, or where few practical hazard reduction or emergency planning
countermeasures exist.
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~ Loss studies in and of themselves do nothing to reduce seis-
mic risk unless they lead to implementation of hazard reduction or
emergency planning measures, or facilitate the development of pub
kc policy. Earthquake loss estimation is an important preliminary
step toward taking appropriate actions for earthquake loss reduction.
This is the most basic purpose underlying earthquake loss estimation.
We study earthquake losses so they can be reduced.
BASIC METHOD
As previously noted, earthquake loss estimates may be made for
many different purposes. Thus, studies may differ as to the types of
losses considered, the extent of the geographical area involved, and
the kinds of facilities included. Facilities ~ a term of broad scope
that includes buildings as well as other structures such as bridges
and utility stations and lifeline systems such as water distribution
networks and airports. The detail in which the analysis is carried
out and the manner in which the losses are aggregated and presented
also may vary. Although the techniques used to carry out various
types of studies may differ, a basic underlying method Is common to
almost all lo~ estimation studies.
The Two Main Components of an
Earthqllalre I~ose E:stNn~tion Stll~y
Figure 1-2 illustrates two components comprising the basic struc-
ture of a loss estimation study. One component, the seismic hazard
analysis, involves the identification and quantitative description of
the earthquake (or earthquakes) to be used as a basis for evaluating
losses. This part of the study falls primarily within the disciplines
of geology and seismology, and this geoscience effort must be coor-
dinated with input from the broad field of civil engineering. The
phrase seismic hazard might seem to refer to all hazards to life and
property posed by earthquakes, but the term has a technical meaning
restricted to the behavior of the ground, apart from any effects on
the built environment.
The second component, the vulnerability analysis, entails analy-
sis of the vulnerability of buildings and other man-made facilities to
earthquake damage and the losses that may result from this damage.
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-
SEISMlg | | VULNERABILITY
\
a\ / I
LOSS
ESTI MATE
FIGURE 1-2 Basic structure of an earthquake loss estimation study.
This effort primarily involves engineers, architects, and experts in
local real estate patterns or socioeconomic, although other disci-
plines (e.g., utility system operators, urban planners, and disaster
preparedness and response specialists) may contribute to identifying
steps that can alter the losses caused by darnage.
The information assembled from these two components is com-
bined to produce the Toss estimate. Close communication among the
technical people undertaking the two parts, and with the intended
users, is vital to ensure proper coordination.
In most Toss estimates, the primary emphasis is on damage and
losses caused directly by the shaking of the ground. The bulk of this
report deals with the evaluation of the ground-shaking hazard and
with the effects of ground shaking on buildings and other facilities.
However, other aspects of the seismic hazard, referred to as collateral
hazards, often are important. They include fault ruptures, landslides,
liquefaction, tsunamis, and seiches.
Landslides may occur in the absence of shaking, but earthquakes
often trigger the sliding of susceptible slop es. Liquefaction is the
state whereby a normally solid soil (saturated with ground water
and usually sands of low density or compaction) turns to a mud-like
or fluid consistency when shaken. Tsunamis are seismic sea waves
(sometimes popularly called tidal waves). Seiches are sloshing or
oscillating waves in bodies of water, generated by earthquakes in
reservoirs, lakes, end enclosed harbors. In some earthquakes col-
lateral hazards may be more destructive than the ground-shaking
hazard, but the technology for evaluating these hazards and their
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effects is not as well developed as that relating to the ground-shaking
hazard.
In a similar vein, most loss estimates focus on the more or less
direct effects of the damage caused by an earthquake: fatalities and
injuries, loss of function, and the cost of repairing damage. Various
other negative effects are called indirect losses. Other types of in-
direct but potentially important consequence of damage include fire
and flooding from dam failure. Another type of indirect consequence
is the economic impact of loss of function on the owners of commercial
property, on the region immediately affected by the earthquake, and
on a larger region economically linked to the affected area. Again,
these losses may be as important as the more direct Tosses, but the
techniques for evaluating them is much more complex and not as well
advanced.
The Ground-Shaking Hazard
The basic building block for a description of the ground-shaking
hazard is a map displaying the intensities of ground shaking over
the study region for an individual earthquake. In general, the in-
tensity will vary over the region, depending on the size and source
characteristics of the event, its location, and local geologic materi-
als and topographical conditions. Such a description is a scenario
earthquake.
Most loss estimate studies use one or several scenario earthquakes
to define the shaking hazard. Loss estunates based on specific earth-
quakes are relatively easy to understand and explain. In addition,
use of specific earthquakes makes it possible to include diverse types
of losses, some of which are best described partially by words rather
than merely by numbers. The use of several such events allows a
range of assumptions and hypotheses to be analyzed and then syn-
thesized in terms of their effects on facilities, without reliance on a
single, perhaps unlikely occurrence.
A more comprehensive but difficult to interpret display of the
hazard consists of calculating the seismic shaking by considering
many possible different earthquakes. Such events can cover a wide
range of magnitudes and locations, and each can be assigned a prom
ability of occurrence.
This approach leads finally to probabilities of occurrence for
earthquake losses. These results can be presented as loss-frequency
curves, which give the annual frequency with which different levels of
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111 10 1
IL
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1 ~
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z 10 5
~5
o
FIGURE 1-3 Loss-frequency curve.
\\
Existing Hazard
Without Mitigation
-
Hazard
With Mitigation ~
-
LOSS
loss are expected to occur (Figure 1-3~. Summing these frequencies
for levels above a specific value gives, for the study region, the annual
probability of exceedance of losses.
Representing the hazard as a loss-frequency curve is ideally
suited for study of the relative merits of various mitigative actions.
That is, loss-frequency curves corresponding to different possible ac-
tions (inclucling no action) may be compared. The method works
best when all the consequences of an earthquake can be expressed
by a single number, such as dollar loss. When multiple losses of
different types are involved, the use of multiple scenario earthquakes
finds wider favor.
Regardless of the number of earthquakes used to represent the
seisrn~c hazard, there is no single, uncontroversial measure of the
damageability of ground motions. For one of the most commonly
utilized measures of intensity—Modified MercaDi Intensity (MMI)
there are even basic disagreements as to the interpretation and defi-
nition of the scale.
A strong need exists for communication at the beginning of a
Toss study among those who will evaluate the ground-shaking hazard
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and ground failures, those who will determine the losses resulting
from that seismic hazard, and those who will utilize the results of
the study.
Venerability
There are two steps in a vulnerability analysis: (1) developing
an inventory of the buildings and other facilities to be considered
in the study, and (2) establishing for each inventory category the
relationships among intensity of ground shaking (and, in some cases
ground failures), resulting damage, and associated losses.
A key step is to develop a list of the categories of facilities to
be considered, that is, to select a classification system. Selection
of this system requires a compromise between different objectives.
On the one hand, a very detailed! classification system, with many
categories, allows fine distinction to be made among buildings with
different seismic resistance. On the other hand, a coarse classification
system with only a few categories simplifies the inventory effort and
makes it more economical. It is also inappropriate for a classification
scheme to divide facilities into many different categories if the un-
derlying state of the art is unable to distinguish among the predicted
performance of the categories. Reaching an optunum compromise
requires close communication among the parties conducting the loss
study.
For purposes of evaluating damage, facilities are usually inven-
toried by placing them in different groups.
Buildings that provide working space or residences for people;
. Lifelines, such as transportation, communications, water,
sewage, and electricity systems, that are vital to the functioning
of an area:
Essential facilities, such as hospitals, and fire and police sta-
tions, that are vital to postdisaster response; and
o Facilities with a potential for large lo - , such as large and
densely occupied buildings, dams, and chemical plants.
Lifelines must be treated differently than buildings because they
form interconnected systems that extend over large areas. Essential
facilities, if they are to be included, must receive more careful atten-
tion and individual surveys and analyses. Facilities with a potential
for large loss pose a very special problem. Clearly their presence and
potential for large Toss must be noted, but losses cannot actually be
estimated without analyses of the likelihood that potential damage
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will actually occur in a given scenario earthquake, and this requires
very detailed study well beyond the scope of a typical loss estimate.
It is easier, for example, to map the area that would be flooded if
a certain dam were to fait than it is to determine whether the dam
actually would fad! in various earthquakes.
CONSIDERATIONS OF UNCERTAINTY
The foregoing discussion has presumed that loss estunates take
the form of scenarios or a los~frequency curve. For the former, one or
more particular earthquakes are postulated to occur, and the losses
expected from each are described. For the latter representation, the
probabilities of various levels of loss are indicated. Whichever method
is used, the uncertainty in the loss estimates should be indicated, such
as by giving a range of possible losses.
The uncertainties in loss estimates derive from several sources.
First is uncertainty in the ground-motion intensity and ground fail-
ures for a given event. Second is uncertainty in estimating damage
given the intensity and ground failures. Third is uncertainty in es-
timating the losses given damage to the facility. Finally there is
uncertainty in the process of inventorying the number of facilities
in each building classification and geographic area. Each of these
elements could be made more precise with additional effort and re-
sources, but uncertainties are inevitable in any practical study of
earthquake losses and should be expressed and quantified.
Representative terms from entire chapter:
loss estimation
