Methods to account for shallow site effects in hybrid broadband ground‐motion simulations

Shallow site effects are indirectly considered in conventional hybrid broadband ground‐motion simulations, and their proper incorporation may be key to improving ground‐motion predictions at soil sites. This article presents and examines five methods to adjust hybrid simulations to account for these effects. These methods use different approaches to modeling site response and require different amounts of site‐characterization data: Methods 1 and 2 use only proxy parameters (e.g. , ) to describe the site conditions, with Method 1 relying solely on proposed site response scaling factors in existing semi‐empirical ground‐motion models, and Method 2 incorporating a host‐to‐target velocity‐profile adjustment; Methods 3 and 4 use a shear‐wave velocity profile along with two different frequency‐domain approaches to predict the linear site response, coupled with the nonlinear component of Method 1; and Method 5 uses 1D time‐domain nonlinear site‐response analysis and generally requires additional data to constrain nonlinear constitutive‐model input parameters. The five methods are applied to four sites subjected to two levels of ground‐motion intensity to illustrate the challenges involved in their implementation and to compare and contrast the resulting adjustments in terms of site amplification. The suitability and performance of each method will depend on multiple factors, including the availability of site‐characterization data and complexity of the site, and hence, their relative advantages and disadvantages are discussed considering a broad range of scenarios.