Click for next page ( 67


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 66
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. 66

OCR for page 66
67 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

OCR for page 66
68 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

OCR for page 66
69 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 valueis 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

OCR for page 66
70 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.

OCR for page 66
71 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

OCR for page 66
~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:

OCR for page 66
73 . 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

OCR for page 66
74 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 wholefrom 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

OCR for page 66
75 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

OCR for page 66
76 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

OCR for page 66
/' 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.