Amplification characteristics at Iedang Reservoir dam sites determined using H/V spectral ratio with background noise, S-wave and coda wave energy

Abstract

Seismograms are mainly composed of three key factors: seismic source, path effects and site amplification characteristics. Among these, amplification characteristics are critical in evaluating the reliability of not only seismic design for engineering but also seismic source and crustal attenuation characteristics for seismology. In this study, the horizontal-to-vertical (H/V) ratio seismogram method was applied. The calculation of the H/V spectral ratio in the frequency domain was first proposed by Y. Nakamura in 1989, and has recently been extended to evaluate site amplification using S-waves, coda waves and background noise. In this study, H/V spectral ratios were analysed using six earthquake seismograms (from earthquakes near Boryeong in Chungnam Province and Baekyeong Island) observed at four temporary dam sites (IDS, IDU, IDD and IDF) near Iedang Reservoir, Korea. We simultaneously compared amplification characteristics, using the S-wave, coda wave and background noise of each seismogram. The simultaneous comparison of S-waves and coda waves (excluding background noise) at the four dam sites showed well-developed consistency in site amplification characteristics. Each site showed different low- and high-frequency characteristics and had its own unique resonance frequency (IDS: ~11 Hz, IDU: ~4 Hz, IDD: ~7 Hz), except for the IDF site, which is situated in hard bedrock. In addition, the IDD site showed first- and second-order site resonance frequency harmonics. We hope that by comparing our results with those from studies using other methods, we are able to add new information to future studies of dynamic behaviour and site classification in Korea.