Abstract To distinguish offshore and onshore seismic ground motions, conventional analyses in terms of peak ground acceleration (PGA) and earthquake response spectrum (ERS) have been carried out in a recent work by authors and other papers in literature. In the present study, distinct temporal and spectral characteristics between onshore and offshore earthquake ground motions are further investigated in time-domain and frequency-domain. The data used is 69 pairs of concurrent onshore and offshore ground motions collected from the Kyoshin Network (K-NET). Each pair of data are of approximately identical epicenter distances. Comparisons are made on zero-up-crossing period (Tz), peak-to-trough acceleration range (Apt) and period (Tpt), duration of ground motion (Td), predominant frequency (fp) and the spectral bandwidth parameter (e). The results indicate that for offshore horizontal and vertical seismic signals, statistics of Tz, Tpt, Td and predominant period Tp tend to be larger than the onshore counterparts. Meanwhile, e of the offshore vertical ground motions is also greater. Through the proposed energy ratio (ER) analysis, the spectral energy of offshore ground motion is found to shift to moderate and low frequency bands. The time-frequency analysis conducted by Hilbert-Huang transform (HHT) shows that the Hilbert spectra of offshore accelerations contain larger spectral energy than the onshore counterpart but the corresponding instantaneous frequencies at peak energy are smaller, especially for horizontal recordings. Therefore, larger dynamic response of offshore structures is prone to be induced by the offshore ground excitation. This is further validated through the dynamic analysis of a marine pipeline in case study.

中文翻译：

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地震地面运动的时间和频谱特征：海上与陆上

摘要 为了区分海上和陆上地震地震动，作者和其他文献论文最近在峰值地面加速度（PGA）和地震反应谱（ERS）方面进行了常规分析。在本研究中，在时域和频域中进一步研究了陆上和海上地震地面运动之间不同的时间和频谱特征。使用的数据是从 Kyoshin 网络 (K-NET) 收集的 69 对同时发生的陆上和海上地面运动。每对数据的震中距离大致相同。对过零周期 (Tz)、峰谷加速度范围 (Apt) 和周期 (Tpt)、地震动持续时间 (Td)、优势频率 (fp) 和频谱带宽参数 (e ）。结果表明，对于海上水平和垂直地震信号，Tz、Tpt、Td 和主导周期Tp 的统计数据往往大于陆上对应的数据。同时，海上垂直地震动的e也更大。通过提出的能量比 (ER) 分析，发现海上地面运动的频谱能量向中低频段移动。希尔伯特-黄变换 (HHT) 进行的时频分析表明，海上加速度的希尔伯特谱比陆上加速度包含更大的谱能量，但峰值能量处的相应瞬时频率较小，尤其是对于水平记录。因此，海上结构容易受到海上地面激励引起较大的动力响应。