Earthquake Spectra

A comprehensive methodology for evaluating the socio-economic impacts of large earthquakes was developed during a three-year project carried out by a team of researchers assembled by the nonprofit organization California Universities for Research in Earthquake Engineering (CUREe). New models were developed for some of the methodology components, such as the identification and ranking of critical facilities. For other components, such as the estimation of building and lifeline component damage, existing models from the ATC-13 and NIBS studies were adopted and modified for use within a GIS environment. The methodology was illustrated through a case study for the city of Palo Alto, California. Damage and loss estimates were made for several earthquake scenarios. Critical buildings were identified and the water distribution system for the city was analyzed in terms of its post-earthquake service capacity. An analysis of the hospital facilities in Palo Alto was made to illustrate the use of benefit-cost analysis for seismic rehabilitation decisions.

Earthquake losses due to highway damage depend not only on the response characteristics of the highway components, but also on the nature of the overall highway system (e.g., redundancies, capacities, traffic demands, etc.). This paper describes recent developments for addressing these issues by using seismic risk analysis (SRA) of the highway system. It outlines a new SRA procedure, describes its application to the Memphis, Tennessee highway system, and summarizes research being conducted to further develop the procedure.

A survey of the seismic hazards for about 30,000 nonresidential buildings in Portland, Oregon was conducted, and an earthquake damage and loss estimation model was developed. To conduct the buildings survey, ATC-21's Rapid Screening Procedure was used. For each building the data included: address, year built, area, number of stories, building name, use, occupancy type, estimated range of number of people, nonstructural falling hazards, building type, and performance modifiers such as soft story and torsion. Soil data were provided by the Earthquake Hazard Maps published by the Oregon Department of Geology and Mineral Industries. The algorithm set up on the GIS was to compute the structural score based on ATC-21 score, modify the score based on the geologic condition of the site, and finally, compute the damage. The proposed loss estimation model is based on ATC-13, and the scoring system developed by ATC-21. The results are in terms of percent (or dollar) damage to buildings in the survey and loss of life and serious injuries.

As a follow on to the Applied Technology Council (ATC) project to develop earthquake damage evaluation data for California (ATC-13 project), ATC has conducted a project to update and translate the ATC-13 data and methodology for use in Salt Lake County, Utah (ATC-36 project). Methodology has been developed and/or updated for: (1) estimation of damage due to ground shaking, (2) estimation of damage due to collateral loss causes such as fault rupture, ground failure, inundation, and fire following earthquake, (3) estimation of time to restore damaged facilities to pre-earthquake usability, and (4) estimation of deaths and injuries. In addition, an electronic inventory of approximately 200,000 structures (buildings and lifeline systems) within Salt Lake County has been developed. The data and methodology have been developed for implementation in a geographic information system (GIS) application, or in a non-GIS software application, such as a relational database management system or spreadsheet.

This paper summarizes the development of a geographic information system (GIS)-based regional loss estimation methodology for the United States funded as part of a four-and-one-half year project by the Federal Emergency Management Agency (FEMA) through the National Institute of Building Sciences (NIBS). The methodology incorporates state-of-the-art approaches for: characterizing earth science hazards, including ground shaking, liquefaction, and landsliding; estimating damage and losses to buildings and lifelines; estimating casualties, shelter requirements and economic losses; and data entry to support loss estimates. The history of the methodology development; the methodology's scope, framework, and limitations; supporting GIS software; potential user applications; and future developments are discussed.

This paper describes building damage functions that were developed for the FEMA/NIBS earthquake loss estimation methodology (Whitman et al., 1997). These functions estimate the probability of discrete states of structural and nonstructural building damage that are used as inputs to the estimation of building losses, including economic loss, casualties and loss of function (Kircher et al., 1997). These functions are of a new form and represent a significant step forward in the prediction of earthquake impacts. Unlike previous building damage models that are based on Modified Mercalli Intensity, the new functions use quantitative measures of ground shaking (and ground failure) and analyze model building types in a similar manner to the engineering analysis of a single structure.

Earthquakes generate a variety of economic impacts. To obtain a consistent measure, the actual damage state must be linked to the dollar losses of the capital stock, and then translated into direct business interruption losses and the ensuing ripple effects that occur throughout the economy. The Earthquake Loss Estimation Methodology (HAZUS) facilitates a consistent set of loss estimations. The direct loss module of HAZUS calculates loss estimates for repair and replacement of building stock (structural and nonstructural), building contents and inventory, and business interruption losses. The direct losses information provides the inputs to the indirect loss module. The indirect loss module estimates the impacts by economic sectors over time and accounts for both earthquake-induced supply shortages and demand reductions. The results of a case study are presented that focus on the economic impacts of various scenario earthquakes that might occur in the Boston metropolitan area.

This paper describes methods for estimating building losses that were developed for the FEMA/NIBS earthquake loss estimation methodology (Whitman et al., 1997). These methods are of a new form and represent a significant step forward in the prediction of earthquake impacts. Unlike previous building loss models that are based on Modified Mercalli Intensity, the new methods use quantitative measures of ground shaking (and ground failure) and analyze model building types in a similar manner to the engineering analysis of a single structure. Direct economic losses predicted by these new methods for typical single-family homes compare well with observed losses to Los Angeles County residences damaged by the 1994 Northridge Earthquake.

Local-scale seismic hazard maps are an important component of loss estimation because they provide information on possible site effects. This paper evaluates how well seismic hazard maps predicted damage in the Northridge earthquake. Normalizing for residential density, the research found that structures built on several geologic map units shown on pre-1994 hazard maps had significantly more damage than the area-wide average. Specifically, buildings on fine-grained Holocene alluvium, hillside bedrock, and “moderate” and “very high” liquefaction susceptibility zones were 1.5 to 2.5 times more likely to be damaged than the area average. Pipes were four times more likely to break in “very high” liquefaction susceptibility zones than in the area as a whole. The use of hazard maps in loss estimation can help state and local governments to set priorities in managing land use, enforcing building codes, conducting seismic strengthening programs for existing structures, and planning for emergency response and longterm recovery.

In recent years, a number of research efforts conducted through the National Center for Earthquake Engineering Research (NCEER) have focused on assessing seismic hazard and vulnerability in the Central United States. These multi-year, coordinated multi-investigator research efforts culminated in two loss estimation demonstration projects for Memphis (Shelby County), Tennessee, that evaluate losses associated with buildings and lifelines, respectively. While conducted independently, these two loss estimation studies share similar approaches, such as the emphasis on using detailed local data. Furthermore, the significance of the projects derives not only from the advances made by individual investigators, but also from the innovations developed in synthesizing the various studies into a coordinated loss estimation effort. This paper discusses the NCEER buildings and lifelines loss estimation projects with emphasis on methodological advances and insights from the loss estimation results.

This paper presents an evaluation of the seismic performance of fire stations in Shelby County, Tennessee. Data relevant to 71 fire stations were collected and implemented as a database using Professional MapInfo. The peak ground accelerations resulting from two scenario earthquakes with moment magnitudes of 6.5 and 7.0 at Marked Tree, Arkansas, were estimated at these fire stations. Furthermore, the fragility curves for various types of buildings in the Memphis area were established based on the fragility data available in the literature. Using these fragility curves, the expected damage to all the fire stations caused by both scenario earthquakes was determined. The results indicate that most of the fire stations will suffer moderate to heavy damage and are expected to be out of operation after the earthquakes. Thus, the authorities need to take appropriate action to mitigate the risks posed by the loss of fire stations.

To support decision-making on upgrading strategies of historic city centres, loss estimation techniques are needed, suitable for application to masonry buildings. This paper describes the development and application of such techniques to a case study in the Alfama District of Lisbon. The project involved a survey of 200 buildings to investigate structural features and condition, mapped using a GIS system, followed by analysis of key collapse mechanisms to define static collapse loads under horizontal forces for each building. The results, obtained in terms of earthquake ground motions likely to produce equivalent damage, led to the development of vulnerability functions for the case study, verified by comparison with functions derived from statistical analysis of world-wide damage reports and with damage reports of the 1755 Lisbon earthquake. The method is used to predict the reduction in losses achieved by the introduction of low-cost unobtrusive strengthening techniques, such as tie-rods connecting facade walls to floors and cross-walls. Cost benefit analysis, considering only structural costs, indicates that the return on the investment would be considerable.

The Universidad de los Andes and the National Institute of Geosciences INGEOMINAS, with the financial support of the national and the municipal governments, have been executing studies to evaluate the seismic hazard and the urban seismic risk for three hypothetical earthquakes that could strike Bogotá, the capital city of Colombia. After having obtained results related to soil amplification using soil dynamic lab studies, analysis of strong-motion records of recent earthquakes and microtremor measurements in a wide area of Bogotá, the study of different scenarios of losses were estimated for different types of buildings and lifelines systems. These earthquake loss estimations have been used by national and local disaster preparedness authorities to design emergency response plans for public information and for educational activities. New requirements are being studied for urban planning, updating the earthquake resistance construction code and for the reinforcement of the seismic rehabilitation of key buildings.

At the time of the Northridge earthquake, a number of new technologies, including real-time availability of earthquake source data, improved loss estimation techniques, Geographic Information Systems and various satellite-based monitoring systems, were either available or under consideration as emergency management resources. The potential benefits from these technologies for earthquake hazard mitigation, response and recovery, however, were largely conceptual. One of the major lessons learned from the January 17, 1994 earthquake was that these technologies could confer significant advantages in understanding and managing a major disaster, and that their integration would contribute a significant additional increment of utility. In the two and half years since the Northridge earthquake, important strides have been taken toward the integration of relatively discrete technologies in a system which provides real-time estimates of regional damage, losses and population impacts. This paper will describe the development, operation and application of the first real-time loss estimation system to be utilized by an emergency services organization.

In estimating the earthquake loss at a given site, procedures have been developed by earthquake engineers for treating the uncertainty arising from lack of knowledge and intrinsic stochastic variability in the local seismic hazard, and in the vulnerability of the property occupying the site. However, in estimating the earthquake loss, not just for a single site, but for a town or county, or for a group of regionally dispersed properties, or for a collection of mobile or portable assets, the treatment of portfolio uncertainty presents an additional statistical challenge to current methodology and practice. Spatial statistical methods are here applied to address portfolio uncertainty; an issue which is particularly important for insurance catastrophe management.