Fragility Curves and Seismic Loss Estimation Methodologies Based on Insurance Data

by R. L. Wesson,
E. V. Leyendecker,
R. V. Roth, Jr.,
D. M. Perkins,

Document Type: Proceeding Paper

Part of: Structures 2001: A Structural Engineering Odyssey


Loss data for single family dwellings from the 1994 Northridge, California, earthquake were correlated with ground motion with the aim of determining ground motion-based fragility curves. The California Department of Insurance collected loss data from insurance companies. The data for each loss indicate the amount and characteristics of the loss above the deductible, typically 10%. The most precise geographic information available for individual losses is the zip code. For each property the earthquake structural loss was divided by the fire structural coverage to estimate a fractional structural loss. Losses greater than 100% are possible when estimated in this manner because many properties were insured for replacement value, suggesting the use of gamma rather than beta distributions. To analyze the correlation of the parameters of the gamma distributions with the ground motion, ground motion estimates at the centroid of each zip code were interpolated from the SHAKEMAP estimates of Wald et al (1999). The a value in the gamma distribution, which controls the width of the distribution, increases with increasing ground motion. The b value has only a weak dependence on ground motion. Future work includes reversing the procedure to determine whether satisfactory estimates of the aggregate structural losses to this class of structures can be made directly from the ground motion, and determining the influence of local site conditions.

Subject Headings: Ground motion | Insurance | Gamma function | Earthquakes | Standards and codes | Curvature | Structural behavior | California | United States

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