Characteristics of the vertical and horizontal response spectra of the Gyeongju earthquake (12 September 2016, ML = 5.8) series

Abstract

ABSTRACTThe response spectra of the 20 Gyeongju earthquake series, including the main earthquake (12 September 2016; ML = 5.8), were compared with the design response spectra (Regulatory Guide 1.60, 1973; United States Nuclear Regulatory Commission) for Korean nuclear power plants and the Korean Building Code (KBC) of 2016 for general structures and buildings. A total of 720 horizontal and vertical accelerations were used to derive the response spectra after normalisation by reference to peak ground acceleration. The horizontal and vertical response spectra were strongly dependent on the epicentral distance and the resonance frequency. When developing design response spectra, it is necessary to consider distances >200 km from the epicenter, given the strong dependence of the response on distance. The vertical responses were consistently lower than the horizontal responses, in good agreement with the various existing seismic design standards and empirical rules. It is essential to develop site-specific seismic design standards, reflecting local seismotectonic environments. Such efforts require large amounts of data covering earthquakes of various magnitudes in the Korean Peninsula and surrounding areas, and such standards should replace Regulatory Guide 1.60. In terms of the KBC 2016, it is necessary to make the criteria more conservative in the short periods, and then to create comprehensive design response spectra by referencing large amounts of qualitative data from the region around the Korean Peninsula on earthquakes of various magnitudes and their effects at different distances from the epicenter.