Until recently, the most commonly used measures for earthquake intensity have been Modified Mercalli Intensity (MMI), and peak ground acceleration (PGA). But PGA is a measure of ground motion, and not of how buildings respond to ground motion. Damage depends rather on the deformation response of the individual structural and non-structural components of a building to ground motion. As an improvement to MMI, spectral displacement (Sd) has recently been chosen as the best measure of ground motion intensity for loss estimation analysis (HAZUS 1997). In order to use Capacity Spectrum Method in earthquake loss risk estimation methods (in the way HAZUS has been used), older MMI-based damage functions (such as ATC-13) can be translated into spectral displacement. In this research, a methodology for translating vulnerability curves from MMI into the spectral displacement format is introduced. Random sampling of the Gutenberg-Richter distribution has been implemented to capture spectral ordinates' dependency on magnitudes and distances. Different attenuation functions and MMI-PGA relationships are examined and their sensitivity is quantified. An example of the implementation of the methodology is given: ATC-13 vulnerability curves developed for MMI are translated into curves based on spectral displacement. Results for all curves are presented.
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