What factors should you consider when conducting a seismic site response analysis?

1 Soil profile

The first factor to consider is the soil profile, which is the vertical distribution of soil layers with different properties, such as density, stiffness, damping, and shear strength. The soil profile determines the depth and frequency of the fundamental site period, which is the natural vibration period of the soil column. The soil profile also affects the amplification or de-amplification of the seismic waves, depending on the impedance contrast between the layers and the bedrock. You should use reliable geotechnical data and methods to define the soil profile and its parameters for the analysis.

2 Input motion

The second factor to consider is the input motion, which is the seismic wave that propagates from the source to the base of the soil column. The input motion should be representative of the seismic hazard at the site, and should include the effects of source characteristics, path attenuation, and regional geology. You should select or generate appropriate input motions based on the design criteria, the seismic code, and the probabilistic or deterministic methods. You should also consider the variability and uncertainty of the input motions, and perform multiple analyses with different scenarios.

3 Analysis method

The third factor to consider is the analysis method, which is the numerical or analytical technique that simulates the seismic site response. The analysis method should be able to capture the nonlinear behavior of the soil, the wave propagation phenomena, and the soil-structure interaction effects. You should choose the analysis method based on the complexity of the problem, the availability of the software and the data, and the accuracy and efficiency of the solution. You should also validate and verify the analysis method with experimental or empirical data, and conduct sensitivity and parametric studies.

5 Uncertainty and variability

The fifth factor to consider is the uncertainty and variability, which are the sources of error and variation in the seismic site response analysis. The uncertainty and variability may arise from the soil profile, the input motion, the analysis method, and the output parameters. You should quantify and reduce the uncertainty and variability by using probabilistic or statistical methods, such as Monte Carlo simulation, fragility analysis, or reliability analysis. You should also consider the uncertainty and variability in the design process, and adopt conservative or robust approaches.