한반도 동남부 주요 지진관측소에서의 다양한 지구물리 시험을 통한 원위치 지반특성 평가

In Situ Site Characterization Adopting Intensive Geophysical Tests at Seismic Stations in Southeastern Korea

There are now many seismic observatory stations, excluding the acceleration monitoring network for infrastructures, of more than 300 operated by several public and governmental organizations across South Korea. The features of the site and properties of the stations were not investigated, and they have been assumed or guessed to estimate the site-specific seismic responses during the 2016 Gyeongju and 2017 Pohang earthquake events. For these reasons, various and intensive geotechnical and geophysical investigations have been conducted to quantify the site characteristics at 15 seismic stations selected in southeastern Korea. The V_S profiles were, at first, obtained by performing only a downhole seismic test (DHT) at 7 stations, and were compared with those from a surface wave method. Then, the shear wave velocity (V_S) profiles were deduced by combining three types of in situ seismic methods composed of a cross-hole seismic test, DHTs, and full-waveform sonic loggings at the 8 other stations, especially to complement the application limits of DHT and reduce the depth-dependent uncertainty in V_S profile. The representative site characteristic profiles for each station regarding V_S and V_P with borehole stratigraphy and density were determined based on robust investigations. Various site parameters related to seismic responses at the seismic stations of interest were obtained for the site-specific geotechnical information, which would be useful to earthquake engineering practices.