Estimating Empirical Site Amplification of Taiwan Near-Surface Structure with CWB Next Generation Seismic Network

• Main Authors: Yu-Hua Liou, 劉玉華
• Other Authors: 馬國鳳
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/6jq353

碩士 === 國立中央大學 === 地球科學學系 === 105 === Site effect is one of the most important factors in evaluating earthquake ground motion. For engineering usage, the ground motion prediction equation (GMPE) usually includes the site-effect factor (e.g. Vs30, Z1.0). The site effect, however, is considered as a non-linear response and could be critical for the aspect in broadband waveform modeling or simulation for ground motion prediction. In this study, I utilize three large earthquakes (ML6.2-6.5) data of both surface and borehole seismometers from Central Weather Bureau (CWB) next generation seismic network to analyze the site amplification factors and the transfer functions of sediments over the basement. A spectral ratio method is used to acquire empirical amplification factors (EAF) for PGA, PGV, and frequency spectra from 0.1 to 10 Hz. The relationship between the EAF and Vs30 value is analyed as well. The results show that the corrections between PGA (or PGV) amplification factors and Vs30 are not significant, suggesting that the amplification of PGA or PGV from borehole to surface was not dominated by shallow structures (i.e., top 30 m of strata). On the contrary, the relationships between EAF for frequency range of 0.1 to 10 Hz and Vs30 are strongly correlated and can be classified into two types. For Type I sites, the EAF increased with increasing frequency, and the Vs30 of these sites are generally over 760 (m/s). Type II sites, with Vs30 generally lower than 760 (m/s), show the peak value of EAF around a frequency range of 1 to 3 Hz that may attribute to the soft-soil conditions. The transfer functions obtained by two deconvolution methods well reconstruct the seismograms of surface stations, which could be used to simulate waveform as site-effect models. The empirical amplification and transfer function analysis could be applied to obtain the GMPE for basement rock and also be adopted in ground motion simulation.