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9
Conclusions and Recommendations
SUMMARY GUIDELINES FOR MULTIPURPOSE,
[ARG~SCA[E EARTHQUAKE [OSS EST=ATES
This chapter presents the panel's conclusions and recornmenda-
tions for conducting general loss estimate studies of the type currently
being funded by FEMA and primarily intended for use by local and
state governments for disaster response and mitigation planning, and
to aid in the formulation and implementation of near- and long-term
strategies for earthquake hazard reduction.
study Preparation and Pawning
The objectives and scope of a study must be defined clearly and
early in a study. Potential users for the study must be identified
and plans made for the ultimate dissemination and utilization of the
report. Specific plans should be made for the involvement of key
local and state personnel throughout the study.
One very important decision at this stage concerns the scope
and detail of the inventory and the form in which it will be prepared.
Discussions should be held with a spectrum of potential users for the
inventory, to identify interest in and commitment to developing and
maintaining an inventory in a computer-based format.
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Scenario Earthquakes
Earthquakes selected for scenarios should be relatively probable
and yet damaging. Using too large and improbable an earthquake
may lead to a Toss of credibility in the loss estimate or create a feeling
of hopelessness in dealing with the high-Ioss estimate. No standard
exists for selecting scenario earthquakes. For the more seismic por-
tions of the country, use of the historical maximum earthquake is
often reasonable. For less seismic areas, probabilistic hazard analysis
is useful. There also is no standard for the choice of a mean recur-
rence interval for a scenario, but intervals of as long as 1,000 years
may be reasonable for disaster response planning, depending on the
intended use. As in seismic design, the more essential or potentially
hazardous the facility or system, the longer the recurrence interval
that is considered. It is desirable that at least a rough indication of
the probability of occurrence be attached to all scenario earthquakes
to convey to users and to the public some indication of the likelihood
of the events.
Despite the problems associated with the use of Modified Mer-
calli Intensity (MMI) scale to prescribe the strength of ground shak-
ing, it still is the best available measure of intensity for use in loss
estunates. More complex representations of ground shaking, for
example, through a filtered detectives peak motion, a s~ngle-degree-
of-freedom linear response spectrum, a nonlinear spectrum, a time
history of motion, and the duration of strong shaking, have the abil-
ity to be more accurate predictors of damage and loss. There is less
agreement, however, on how to estimate these functions for a future
earthquake, how to quantify the single- or multidimensional hazard
associated with them, and how to derive an accurate predictor of
damage from them.
However, use of MMI XT and XIT should be avoided, or at least
the meaning of these intensities should be carefully defined if used.
The ground conditions for which prescribed intensities apply must
be stated clearly, together with rules for taking into account below-
or above-standard ground conditions.
Classification System for Bu~dinge
The primary purpose of a classification system is to group build-
ings according to their seismic resistance for Toss estimation purposes.
Choice of a classification system depends on the availability of infor-
mation relating ground motion to damage and on the funds available
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for compiling an inventory. Several standard classification systems
have been developed, primarily for California construction, but in
general it is necessary to tailor the system to suit local conditions.
Inventory
Inventory preparation is generally the most time-consuming and
expensive aspect of a loss study. It is an exercise in locating and
using available sources of information, carrying out some onsite in-
spection, and applying considerable judgment. The most difficult
step is identifying the seismic resistance category for a building or
group of buildings. Methods have been developed for abstracting an
inventory from socioeconomic data in national data bases, but the
pane! believes that loss estimation efforts are better spent on field
surveys and compilation of harder, more accurate construction class
data.
It generally is not feasible to inventory all buildings individu-
ally, and attention is better focused on buildings that are seismi-
cally suspicious or are important to emergency response following an
earthquake. Even when buildings are inventoried individually, they
may subsequently be grouped regarding estimated losses, to help
avoid legal and political problems that may result from singling out
specific buildings as being hazardous. On the other hand, failure to
disclose information about hazards may increase liability exposure,
so the issue of specificity of an inventory should be handled with legal
advice.
It is important to disaggregate the loss estimates to the smallest
relevant political unit, except where this results in a small number of
facilities that would compromise either the anonymity or statistical
validity of the results.
Motion-Damage Relationships
The best information relating ground motion to damage are
the statistics developed by the Insurance Services Office (ISO) from
actual earthquake experiences. This information takes the form of
average property loss ratios for selected classes of buildings versus
intensity of ground shaking. The available data are best for single-
fam~ly, wood-frame dwellings, and apply directly only to construction
in California and some other western areas.
Because actual data of this type are so limited, and because
for some purposes it is important to estimate the distribution of
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damage as well as the mean damage, damage probability matrices
(DPMs) and fragility curves have been developed as alternatives to
mean loss curves. Using a formalized procedure for obtaining and
processing expert opinion, the Applied Technology Council (ATC)
has published DPMs for a wide range of types of structures found in
California. When the construction classes of ISO and ATC overlap,
mean loss ratios deduced from the ATC DPMs are very similar to
the curves of ISO.
The ambitiousness of the ATC-13 project has led to impressive
accomplishments although the pane! identified some criticisms of
the method used to develop the ATC DPMs and of the manner in
which they are portrayed. The final report of ATC-13 combines
in one volume more data, a more complete methodological review,
and more discussion by experts of the various tasks involved in the
earthquake loss estimation process than any other single publication.
A major question is: How should motion-damage relationships
be developed for use in loss estimates in areas other than California?
The pane! recommends that expert opinion be used to modify the
California-based information for the types of buildings found in the
area to be studied. Limited analysis of some selected archetype
buildings can assist in this effort.
Evaluation of Losses
Combining the inventory with motion-damage relations leads di-
rectly to estimates for property losses, although it is necessary to
be careful and explicit as to what value of buildings replacement
cost or market value—is used in the calculation. Usually, however,
it is also necessary to estimate numbers of casualties. The data on
which to predict deaths and injuries are very sparse, and considerable
judgment is necessary in organizing available information to estimate
casualties. The pane] prefers a method set forth by ATC in which
casualty rates are linked to degree of damage and class of construc-
tion; this is a rational approach but must be used with considerable
judgment.
Estimates for the number of people requiring shelter are also
important for planning of postdisaster operations, and for this pur-
pose as well as for casualty prediction it is necessary to forecast the
amount of severe damage rather than just the mean overall Toss.
Any study should give a realistic assessment of the uncertainty
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in all loss estimates, such as by giving both best estimates and likely
ranges.
Collateral Hazards
In addition to losses caused by shaking of buildings founded
on stable ground, there may be losses caused by collateral hazards
such as fault ruptures, landslides, liquefaction, tsunamis, and seiches.
Losses from collateral hazards can be very important, in some cases
dominating the overall loss. The key to evaluating these losses is in
the identification of areas where such hazards will occur as a result of
the scenario earthquakes. Unfortunately, to do this systematically
is a major and expensive task, and it may be necessary to rely on
the judgment of experts. ATC has developed a rational sequence of
steps for developing DPMs for structures affected by ground failure,
once such areas have been identified by geologists and geotechnical
engineers.
Lifelines and Emergency Facilities
In addition to buildings for residence and work, many other types
of facilities are potentially important in loss estimates. Lifelines
(e.g., railroads, highways and streets, water, electricity and sewage
systems, and communication services) are vital to the functioning
of a region and its emergency response capabilities following an
earthquake.
Evaluation of lifelines involves the study of the possible failures of
components (e.g., bridges or segments of pipelines) and the analysis
of the effect of such individual failures on the overall performance
of the system. The ATC-13 report has DPMs for various types of
lifeline system components, which are the best available guidance,
and the recent reports by the Building Seismic Safety Council (1987)
are useful as well. For many lifelines, computer models for evaluating
the effect on overall performance of the loss of some components will
be available from utilities or agencies responsible for the lifelines,
and the active cooperation of such utilities and agencies is the key
to a satisfactory lifelines loss estimate. The final result is a scenario
describing the ability of each lifeline to provide service following the
earthquake.
Special attention must be given to those installations most es-
sential for emergency response, such as fire stations and hospitals.
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Susceptibility to structural damage must be assessed, but even if
there is no structural damage a facility may be unable to function
effectively if critical equipment has been dislodged or if important or
dangerous contents have been damaged. It generally is necessary to
visit each facility to assess structural resistance, and also to view the
state of nonstructural conditions. ATC-13 contains organized expert
opinion as to the time required to restore functionality of facilities,
but the pane! feels that these quantitative estimates contain more
uncertainty than most other aspects of the overall process.
Even though each emergency facility is inventoried, legal and
political difficulties generally require that a number of such facilities
be grouped when stating expected losses. Thus, the result is a sce-
nario describing the functionality of the emergency response systems
as a whole, broken down by subareas, and not the state of individual
facilities.
Facilities with a Potential for Large [oss
These facilities are not numerous and failure could cause enor-
mous casualties as well as major property loss. Unless the loss and
its likelihood can be stated with confidence as the result of detailed
(and expensive) analysis, it should not be included in a large-scale
loss estimate. However, the existence of such potentially hazardous
facilities should be highlighted in the report.
Correct Dosses
It is not yet possible to make reliable quantitative estimates of
the potential losses from fire following an earthquake, but a study
should emphasize the functionality of the water supply system and
the highway and street infrastructure as they relate to firefighting
capability. It should also note high-risk areas or factors, such as time
of year and weather. This has generally been done in the studies
conducted by the National Oceanic and Atmospheric Administration
and the U.S. Geological Survey. Precise quantitative loss estimates
are not always necessary to point the way toward improvements in
hazard reduction and emergency planning efforts.
An inventory of hazardous materials is desirable, but its prepara-
tion will depend on state and local inventories and existing programs
of environmental health agencies and fire departments. There is no
satisfactory method for evaluating the likelihood that storage systems
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~2
will fail and cause release of these substances, and so this problem
should be treated similarly to the topic of fires.
Evaluation of economic impacts other than damage is usually
not part of a general-purpose loss estimate.
The Report
The report of a loss estimate study should meet two objectives.
First and foremost, it should present results in a manner under-
standable to users in state and local government and to the public.
Second, it should document the technical procedures used to compile
the inventory and to calculate or otherwise evaluate losses, so that
in the future the loss estimate can be updated. Careful design of the
report is essential to achieve these two different and often conflicting
objectives.
Independent Guidance and Review
Experts unaffiliated with the organizations conducting a loss
study should provide independent guidance and review of an earth-
quake loss study. This policy is recommended for budgeting and
implementation in future federally funded loss studies. The guidance
and review might best proceed in steps a review of the user-defined
goals for the study, a review of the seisrn~c hazard analysis, a review
of the design for the inventory process, and so on. The final results
of the study should also be reviewed.
This independent review is not suggested out of concern over the
quality of past projects but to increase confidence in the results of
future studies, to ensure better documentation of the methods used,
and to conform to validation procedures generally accepted in the
scientific and engineering disciplines.
User Needs
The foregoing guidelines respond to several of the identified user
needs: involvement of local personnel, selection of the scenario earth-
quakets), establishment of inventories with continued use for multi-
ple purposes, disaggregation of inventory and losses to the smallest
political unit consistent with the principle of averaging losses over
an adequate number of facilities to ensure statistical validity and
anonymity, and the reporting of the loss study results.
Several user recommendations conflict with the state of the art:
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. Presenting a single number loss estimate rather than present-
ing a range of possible losses. Loss est~rnates are quite approximate,
and it is considered essential that the uncertainty in any estimate be
reported.
Identification of specific, seismically suspicious buildings,
structures, or facilities. In the absence of enabling legislation, identi-
fying specific buildings as being likely to sustain damage could expose
a loss estimator to legal suits or political repercussions. To be con-
fident about the likely performance of a specific building involves a
thorough study beyond the scope and budget of most loss estimates.
Identification of expected releases of hazardous substances.
In addition to the difficulties mentioned above, experiences during
actual earthquakes are too limited to peanut confident predictions.
At the outset of any study, the potential users and those per-
form~ng the Toss estimate must agree on compromises between what
is desired and what is feasible.
Cost and Commitment Sharing
The pane! is unable to provide guidelines as to the appropriate
cost of a loss estunation study. It has been noted that a larger loss
study budget can be justified on technical grounds because it leads
to more accurate results. Another appropriate criterion for gauging
how much should be spent on loss estimates ~ how extensively the
information will be used. The political ramifications of cost sharing
are also beyond the scope of the panel's review, but the related idea
of commitment sharing should be considered in any debate over cost
sharing.
While no one can promise that a loss study will lead to the
passage of improved building or land-use ordinances, it is possible
to schedule statewide conferences, as well as legislative briefings,
for building officials and city planners following the completion of
a loss study to consider its implications. State and local offices of
emergency services can be expected to take a new loss study's findings
into account in their earthquake disaster response planning, and this
emergency plan revision effort can be scheduled to begin when the
Toss study is completed. Distribution of copies or summaries of
the study and public information efforts can also be budgeted and
planned prior to completion of a study. In the words of one observer
and participant in the process of producing and implementing a Toss
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estunate study, "Users should be required to commit themselves to
the use of the information" (Buck, 1978~.
RECOMMENDATIONS FOR RESEARCH AND
DEVELOPMENT
Validation of [oss Estunation Methodologies
A strong need exists to demonstrate the validity of the com-
ponents of the current loss estimation technology as well as the
technology as a whole. Therefore, the pane] makes two recornrnen-
dations.
1. Following the next damaging earthquake to strike an urban-
ized area in the United States, after-the-fact ~predictions" should be
made using one or more predictive methods and results compared
with the actual losses. The goals are to establish confidence in the
use of the methods and to learn how the methods might be improved.
The comparisons should be made for the methods as a whole—from
magnitude and location to loss and also for various components,
such as losses estimated vi~a-vis a given intensity.
2. Opportunities should be seized for evaluating components of
the overall methodology. Two examples from the inventory part of
the problem are:
Where an exact inventory exists, such as with unrein-
forced masonry buildings in Los Angeles, compare these hard data
with the inventories established by approximate methods;
Where an approximate loss estimation inventory has been
prepared for a region, and this inventory can be disaggregated to
small areas, prepare for comparison a complete inventory of one or
more categories of buildings for a small area
Corresponding opportunities will occur for other components of
an overall methodology, for example, predicted and actual intensity
of ground motion, or comparison of maps showing probable ground
failure zones with maps locating actual failures prepared after an
earthquake.
Sensitivity Analysis
For one or more methods, the pane! recommends conducting
sensitivity analyses to identify the significance of various possible
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errors on the overall loss estimate at each stage in the process.
Such a study will give greater understanding of the uncertainty in
loss estimates and wall identify the parts of the overall process that
contribute most essentially to this uncertainty. Such studies should
be done using methods involving different degrees of approximation,
and the resulting differences in the mean and ranges of estimated
losses contrasted with the effort to prepare the estunate.
Development of Unproved Methods
The ATC-13 report and other recent studies have made excellent
contributions toward development of improved methods for evaluat-
ing losses. Continuation of this work will lead to improved methods
with wide applicability. Thus, the pane! recommends:
.
A concerted effort should be made to develop a construction
classification system applicable throughout the United States.
~ Existing inventory methods should be compared to synthe-
size their strong points, rather than developing another new method.
The NOAA-USGS method has featured the use of experienced earth-
quake engineers and locally knowledgeable real estate consultants or
building officials to field sample a study area and relate the samples
to land-use maps. The inventory method that would be most com-
monly used in the ATC-13 approach (Level 2), while not generally
recommended by the panel, may be promising in combination with
some field data to produce preliminary inventory outlines that would
be used to design the detailed inventory process. The Gauchat and
Schodek (1984) study of Boston housing, and the work by Jones et
al. (1986) in Wichita, Kansas, incorporated aerial photography into
the inventory process. While the panel does not recornrnend the use
of aerial photography alone, it may be usefully combined with other
data sources.
~ The motion-damage-Ioss component of various methods
should be compared to synthesize their strong points, rather than
developing another new method. ATC-13 is innovative in its struc-
tured use of expert opinion and its development of relationships for
new construction classes. The NOAA-USGS method has capitalized
on historical loss data as well as judgment. The Central U.S.-Six
Cities study (Allen and Hoshall et al., 1985) and the study of Boston
housing earthquake vulnerability (Gauchat and Schodek, 1984) are
notable for their explicit description of the archetype buildings that
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represent each construction class, allowing experts to analyze thor-
oughly and debate the vulnerability of each class- with the definition
of the class held constant.
While work aimed at developing improved methods for estimat-
ing building losses should continue, special emphasis should be given
to collateral hazards, such as ground failure and water effects, in-
cluding the damage caused by such hazards, and to lifelines and
emergency facilities.
As part of this effort, there should be a renewed attempt to
develop a satisfactory quantitative scale for the damaging potential
of ground motion. It is likely that using more than a single ground-
motion parameter will be necessary. The pane! accepts the use of
MMI, but sees the possibility of developing an improved substitute.
Users' Needs and Study Uses
Research should be conducted to document exactly how previous
loss studies have been used. For example, in what precise ways is a
city's disaster response plan different because of the existence of a
loss study? What public policy decisions were directly affected by a
study?
In parallel with the development of improved loss estunate
methods there should be unproved utilization of study results. The
problem is not just lack of information, but also lack of use of infor-
mation.
Collection of Earthquake Lose Data
The process of collecting loss data immediately after significant
earthquakes needs to be improved. For example, while reconnais-
sance efforts are common, collection of good-quality damage data
and information on casualties, property loss, and functional loss re-
quires noting the performance of all buildings of a given type in a
given area. Documenting the performance of only the small number
of buildings that experience dramatic damage does not provide the
needed statistics.
As long ago as the 1923 Yokohama and Tokyo earthquake in
Japan, or the 1933 Long Beach, California earthquake in this coun-
try, thorough field surveys of damage have been conducted. The
techniques are readily available, but the administrative program
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/'
to Add Ed public thy statists type of dam bus oRen been
l~klug.
In addition, empb-6 must be plied on c~lechug dam Or the
occurrence Ed nonoccurrence of cowherd bawds, the per~rm~ce
of lifelines, nonstructural components, and emergency Scribes, Ed
the containment or release of b==dous substances.
Representative terms from entire chapter:
loss estimates
