| 英文摘要 |
Site effects are one of the most important aspects of engineering seismology studies. Traditionally, considerable efforts have focused on horizontal, rather than vertical, motions because the contribution of shear waves to seismic energy is higher and easily correlated with seismic disasters and loss estimation. Researchers are mostly familiar with horizontal site responses for seismic hazard evaluation of a specific site (e.g., power plants) and commonly generate a 1/2th to 2/3rds reduction for vertical motions in the general region and near-fault region, respectively. However, the empirical relationships for horizontal motion still lack sufficient observation and theoretical support. Meanwhile, vertical site responses have received more attention in recent years in site-specific studies through the use of vertical-to-horizontal strongmotion models. In Taiwan, a horizontal seismic hazard of a shear wave velocity of 760 m/s for generic rock conditions has been established and other applications of vertical motions have commenced. Basic concepts of seismic wave propagation suggest that vertical motion should primarily be associated with P waves, which would imply that most seismic events are adequately characterized by P-wave-related parameters (including bulk modulus, P-wave velocity, and vertical kappa) and that S-wave-related parameters (such as Young’s modulus, S-wave velocity, and kappa) are not required. In order to verify this, the frequency content of vertical motion should be investigated. This study analyses the Fourier amplitude spectra (FAS) energy associated with vertical motions of Taiwanese earthquakes. The FAS study indicates that most of the energy was generated from shear waves and not from compressional waves even in vertical motion, and this needs to be considered in hazard evaluation in Taiwan. Finally, rock sites in Taiwan with Vs30 of 600-900 m/s were evaluated to compare vertical site responses. |
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