Development of Korean Design Spectrum Based on the Domestic and Overseas Intra-plate Earthquake Records

Abstract

In this study, the standard design spectrum for Korea, which is known to belong to an intra-plate region, is developed from the ground motion records of the earthquakes occurred in domestic and overseas intra-plate regions. The horizontal spectrum is defined as GMRotI50. From the statistical analysis of the GMRotI50 and the vertical response spectra, a mean plus one standard deviation spectrum in lognormal distribution is obtained. Regression analysis is performed on this curve to determine the shape of the design spectrum. The developed design spectrum is valid for the estimation both spectral acceleration and displacement. The ratio of vertical to horizontal response spectrum for each record is calculated. Statistical analysis of the ratios rendered the vertical to horizontal ratio (V⁄H ratio). Subsequently the ratio between the peak vertical ground acceleration to the horizontal one is obtained. On September 12, 2016, Gyeongju earthquake and November 15, 2017, Pohang earthquake occurred. Its local magnitude was announced to be 5.8 and 5.4, respectively. Ground motion data recorded at KMA, EMC, KERC stations was obtained from the database of them. Applying the same procedure, horizontal and vertical response spectra, and V⁄H ratio were calculated. These results were compared with the standard design spectra, which were newly developed in this study. The response spectra of Gyeongju and Pohang earthquakes were found to be almost identical with the newly proposed design spectra. Even the V⁄H ratios showed proper agreement. These results confirmed that the method adopted when developing the standard design spectra were valid and the developed design spectra were reliable.