ABSTRACT

The high‐frequency spectral decay parameter kappa (κ) is estimated for the Gyeongju area using records of the temporary seismic array in the Gyeongju area (TSAG), which operated from 2010 to 2013. Gyeongju is a city located in the southeastern part of the Korean Peninsula. Moderate earthquakes frequently occurred around the Gyeongju area in the past; the area has experienced numerous earthquakes for more than a year since an earthquake of ML 5.8 occurred in Gyeongju on 12 September 2016. It is also an important place from an engineering point of view because nuclear facilities are located in the area. The high‐frequency spectral decay model of Anderson and Hough (1984) and the standardized procedure for the κ‐estimation suggested by Ktenidou et al. (2013) are applied to estimate κ for the Gyeongju area. The estimation gives rise to the equation, κ=0.0219(±0.00151)+7.56×105(±1.45×105)R indicating that the site‐specific κ0‐value and the slope κR are 0.0219 s and 7.56×105 s/km, respectively, for the Gyeongju area. The κ‐estimation for individual stations of TSAG was done to obtain the site‐specific κ0‐values of stations. Despite the close distance between TSAG stations, the site‐specific κ0‐values of each station vary. Other than TSAG, κ is also estimated for the permanent borehole station HDB, which has been operated by the Korea Institute of Geoscience and Mineral Resources and is located in the Gyeongju area. The estimated κ0‐value of 0.0178 s for HDB is smaller than that of TSAG by 0.0219 s. This is because HDB is a borehole station, but all stations of TSAG are installed at surface. The variation of the κ0‐values among the individual TSAG stations and the difference between κ0 for TSAG and that for HDB indicate that spectral decay characteristic at high frequency is affected by surficial sediment layers.

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