Seismic site response of shallow sites in moderate seismicity regions

Seismic site response is highly dependent on local soil conditions that significantly influence amplification and attenuation of rock motions during a seismic event. Local site effects have been studied extensively in regions of high seismicity, low impedance contrast, and deep soil profiles. In moderate seismicity regions, rock motions with low intensity, short duration, and high frequency content might experience significant short period amplification while propagating through shallow sites with high impedance contrast. Building code-based site factors and design spectra may not accurately capture such short period amplification in moderate seismicity regions such as Korea, thus may lead to non-representative seismic site response estimates. This paper presents the results of numerical simulations of seismic site response of shallow soil sites (<30m) with high impedance contrast in moderate seismicity regions. Seismic site response is computed through series of equivalent linear and nonlinear analyses performed for four representative shallow sites from Korea for moderate seismicity events. This paper compares the computed seismic site response with building code-based design estimates and discusses potential implications of observed differences on design practice.