ABSTRACT

The traditional approach used to incorporate site response into the ground‐motion hazard analysis is to compute a design spectrum for a rock‐site condition and then propagate the rock motion from the base of the soil model to the surface. The main limitation with this approach is that it can be inconsistent with the ground‐motion models (GMMs) used to develop the input rock motion. The VS profile implicit in the GMMs is unlikely to match the site‐specific VS profile (value and gradient), because the GMMs were developed for ground motions from different VS profiles over large regions and are unlikely to match the profile of any one site well. This article presents the VS profile correction method for developing surface ground motions as an alternative to the soil‐over‐rock approach routinely used in earthquake engineering practice. This approach is similar to the standard soil‐over‐rock analysis, but uses different input motions and involves performing two site response analyses—one for the generic profile associated with the GMM(s) and one for the site‐specific profile—then applying the ratio of the two site response analysis results to correct the design spectrum for the reference site condition developed using the GMMs. Two example applications are included to illustrate the VS profile correction methodology as well as some of the challenges that may arise when doing so.

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