Craig Taylor

Direct Economic Losses in the Northridge Earthquake: A Three‐Year Post‐Event Perspective

The Northridge earthquake will long be remembered for the unprecedented losses incurred as a result of a moderate-size event in a suburban area of Los Angeles. Current documented costs indicate that this event is the costliest disaster in U.S. history. Although it is difficult to estimate the full cost of this event, it is quite possible that total losses, excluding indirect effects, could reach as much as

Epistemic uncertainty, rival models, and closure

40 billion. This would make the Northridge earthquake less severe than the Kobe event, which occurred exactly one year after the Northridge earthquake, but adds a bit of realism that a Kobe-type disaster is possible in the U.S. This paper attempts to put into perspective the direct capital losses associated with the Northridge earthquake. In doing so, we introduce the concept of hidden and/or undocumented costs that could double current estimates. In addition, we present the notion that a final estimate of loss may be impossible to achieve, although costs do begin to level off two years after the earthquake. Finally, we attempt to reconcile apparent differences between loss totals for two databases tracking similar information.

Toward System Performance Standards for Infrastructure Systems Impacted by Natural Hazards

In catastrophe risk and probabilistic hazard evaluations, one overarching issue is how to account for uncertainties. One influential school of thought employs a sharp distinction between aleatory (pertaining to randomness) uncertainty and epistemic (pertaining to knowledge) uncertainty, and uses this distinction to derive total uncertainty in risk and probabilistic hazard evaluations. This paper first critiques two quantitative versions of this sharp distinction. The first version applies only to single models. The second version applies to a weighted combination of rival models. This paper shows that serious contradictions and biases arise for each version, as elaborated by its advocates. Given these contradictions and the need to address the overarching issue of uncertainties in risk evaluations, this paper goes on to sketch an alternative approach called robust simulation, which applies to catastrophe risk and probabilistic hazard results. Robust simulation first develops results from a single preferred model, and then proceeds to find and evaluate results from the most divergent yet credible rival models. In addition to producing many simulations from models, this approach also tests resulting distributions in terms of their stability.

Sample Treatment of Uncertainties in Earthquake Portfolio Risk Analysis

Even though many disciplines familiar to the audience may have adopted a systems approach to the development of standards, the same is not currently widespread for natural hazards standards for infrastructure systems and components. Beginning with the formation of American Lifelines Alliance (ALA), this paper emphasizes the evolution of attempts to promote a systemic approach to performance standards for components in infrastructure systems. Covered are selected projects performed through ALA. In addition, projects for the Multidisciplinary Center for Earthquake Engineering/Federal Highway Administration (MCEER/FHWA), the California Department of Transportation (CALTRANS), the Port of Los Angeles, the Port of Oakland, San Francisco International Airport, and the United States Geological Survey (USGS) indicate the importance of a systemic approach to the development of standards for components in infrastructure systems. At the same time, reasons are provided as to why the notion of system performance standards have not yet been more widely extended to natural hazards generally.

Seismic Code Decisions under Risk: The Wasatch Front Illustration

Previous papers and presentations by the authors have proposed that robust simulation should be used to define uncertainties in catastrophe risk analyses for portfolios and/or systems. Robust simulation begins with a “preferred” comprehensive model that turns out to be comprised of non-unique solutions for many technical issues. Uncertainties in this “preferred” model can be estimated either endogenously, that is, through alternative distributions used in the simulation process, or exogenously, through alternative comprehensive model simulations. This paper elucidates how these uncertainties are estimated through the examination on the one hand of available earthquake hazard models and (e.g., GMPE, kinematic) and selected uncertainties (e.g., directivity, focal depth), and on the other hand of available building vulnerability models (statistical, opinion-based, engineering) and selected uncertainties (e.g., structural period, strength, ductility). The goal of this paper is thus to define more clearly what count as “alternative credible models” and how they may be used to estimate uncertainties in the resulting portfolio loss distributions. BACKGROUND In recent years, the overarching question “How does one account for uncertainties in catastrophe risk analysis?” has become more prominent. Within traditions of statistical and probability theory, the narrow tradition of using the distinction between “epistemic” and “aleatory” uncertainty has been demonstrated to yield considerable incoherence. Endogenous or nominal uncertainties account for uncertainties given the models used, but not those uncertainties resulting from the use of alternative models (parameters, data, or assumptions).

Assessing seismic response of Utah gas systems

Regions of low-to-moderate seismicity but high catastrophic earthquake loss potential pose special issues with respect to seismic design codes as well as other significant policy decisions. These seismic design code decisions hinge on the amount of initial costs and on the size and certainty of benefits from increased design requirements. Since these decisions are made by government officials, these costs and benefits are distributed among various stakeholders in the community. This paper explains this perspective and clarifies earthquake risk methods needed to address these seismic design force level decisions in the Wasatch Front, Utah and, as a point of comparison, to the City of Los Angeles. These applications strengthen the case for a seismic zone 4 designation along the Wasatch Front but also raise issues about the roles of life-safety protection and certainty of benefits in seismic code decisions.

Benefit-Cost Analysis of FEMA Hazard Mitigation Grants

The potential damage to lifelines from even moderate earthquakes can have significant and widespread effects on community well-being. Recently, under the sponsorship of the United States Geological Survey, researchers from California cooperated with a utility in Utah to analyze the seismic safety of natural gas facilities in Utah. They identified pipelines by system importance, size, and material, and then assessed the probability of structural damage to these components. These estimates, which reflect knowledge of Wasatch Front fault mechanisms, and an ability to model numerous seismic events by computer, are yielding significant knowledge of possible piping responses. Project results included the number and location of possible pipeline breaks for various seismic events. This information was used to estimate gas loss and resultant system pressures. This, in turn, is currently being used to guide future system reinforcements, replacements, and installation of emergency system isolation valves. This project, involving the close interaction of both the utility and the research firm, is a good example of the type of practical research needed by industry.