Teleseisms as Estimators of Experimental Long‐Period Site Amplification: Application to the Po Plain (Italy) for the 2011 Mw 9.0 Tohoku‐Oki (Japan) Earthquake
Teleseisms as Estimators of Experimental Long‐Period Site Amplification: Application to the Po Plain (Italy) for the 2011 Mw 9.0 Tohoku‐Oki (Japan) Earthquake
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DOI：
10.1785/0120120164
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发表时间：
2013-10
影响因子：
3
通讯作者：
M. Massa;P. Augliera
中科院分区：
文献类型：
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作者：
M. Massa;P. Augliera
摘要 本研究的重点是评估远震作为大型冲积盆地长周期地震站点放大的估计量。利用 2011 年 3 月 11 日日本东北冲城 M w 9.0 地震的记录，对意大利波平原的低频现场响应进行了调查。与东北冲波形相对于目标区域的行进路径相比，分析地点之间的间距使我们能够研究应用于远震记录的标准谱比（SSR）技术的可靠性。结果以定向 SSR 的形式呈现，计算结果考虑了 2 分钟的 P 波、S 波和瑞利 (LR) 波，并从 0.025 Hz 到 1.0 Hz 进行滤波。考虑到水平分量，频率为 0.04 至 0.3 Hz 时，波平原站的 S 和 LR 相位分别检测到放大系数高达 20 和 16。在某些情况下，放大的地面运动似乎受到极化现象的影响，特别是在南北方向。从盆地中心向边缘移动，LR波放大显着减小，特别是对于0.1和0.3 Hz之间的频率；对于 S 波没有观察到这一点。随着谐振周期从 P 波向 LR 波移动，垂直分量的放大系数也大于 10。将 SSR 与单站水平与垂直频谱比进行比较，后一种情况表明，垂直放大会导致站点实际响应的部分屏蔽，特别是对于频率 >0.15 Hz 的情况。最后，还研究了相对 P 波振幅。频谱分析的结果以及相对纵波振幅与基岩几何形状之间的相关性表明，所提出的方法适用于研究类似环境下的长周期地震场地响应。
Abstract This study focuses on the evaluation of teleseisms as estimators of long‐period seismic site amplification in correspondence to large alluvial basins. Using the recordings of the 11 March 2011 M w 9.0 Tohoku‐Oki, Japan, earthquake, the site response at low frequency of the Po Plain, Italy, was investigated. The interdistances among the analyzed sites, compared to the travel paths of the Tohoku‐Oki waveforms with respect to the target area, allowed us to investigate the reliability of the standard spectral ratio (SSR) technique applied to teleseismic recordings. The results are presented as directional SSRs calculated considering 2 min of P , S , and Rayleigh ( LR ) waves, filtered from 0.025 to 1.0 Hz. Considering the horizontal components, at frequency from 0.04 to 0.3 Hz, the Po Plain stations show amplification factors up to 20 and 16, detected for the S and LR phases, respectively. In some cases, the amplified ground motion appeared to be affected by polarization phenomena, in particular in the north–south direction. Moving from the center to the edge of the basin, the LR ‐wave amplification remarkably decreases, in particular for frequencies between 0.1 and 0.3 Hz; this was not observed for the S wave. Amplification factors >10 were also detected for the vertical component, with increasing resonance periods moving from P to LR waves. Comparing SSRs with the single‐station horizontal‐to‐vertical spectral ratios, the latter case shows that the vertical amplifications lead to the partial masking of the actual response of a site, in particular for frequencies >0.15 Hz. Finally, the relative P ‐wave amplitudes were also investigated. The results of the spectral analysis and the correlation between the relative P ‐wave amplitudes and the geometry of the bedrock suggest that the proposed approach is appropriate for the investigation of long‐period seismic site response in similar settings.