Site Amplification and Attenuation via Downhole Array Seismogram Inversion: A Comparative Study of the 2003 Miyagi-Oki Aftershock Sequence
Site Amplification and Attenuation via Downhole Array Seismogram Inversion: A Comparative Study of the 2003 Miyagi-Oki Aftershock Sequence
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井下阵列地震图反演的现场放大和衰减：2003年宫城冲余震序列的对比研究
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
K. Tsuda
中科院分区：
文献类型：
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作者：
D. Assimaki;Wei Li;J. Steidl;K. Tsuda
本文利用日本强震网络KiK-Net的38个台站在2003年m_w7:0宫城- oki余震序列上的弱运动地质技术阵列记录，量化了近地表地层对入射地震运动的放大和衰减效应。首先，实现了一种地震波形优化算法，用于评估感兴趣地点的高分辨率、低应变速度（V_s）、衰减（Q_s）和密度（ρ）剖面。基于反演结果，建立了V_s与Q_s的相关性，并在其物理解释中考虑了散射与本征衰减效应。然后评估和比较地面-井下传统光谱比（SSR）、交叉光谱比（c-SSR）和水平-垂直（H/V）现场响应估计。
Weak-motion geotechnical array recordings at 38 stations of the Japanese strong-motion network KiK-Net from the 2003 M_w 7:0 Miyagi-Oki aftershock sequence are used here to quantify the amplification and attenuation effects of near-surface formations to incident seismic motion. Initially, a seismic waveform optimization algorithm is implemented for the evaluation of high-resolution, low-strain velocity (V_s), attenuation (Q_s), and density (ρ) profiles at the sites of interest. Based on the inversion results, V_s versus Q_s correlations are developed, and scattering versus intrinsic attenuation effects are accounted for in their physical interpretation. Surface-to-downhole traditional spectral ratios (SSR), cross-spectral ratios (c-SSR), and horizontal-to-vertical (H/V) site-response estimates are next evaluated and compared,
while their effectiveness is assessed as a function of the site conditions classified on the basis of the weighted average Vs of the upper 30 m (V_(s30)) of the formations.
Single and reference-station site-response estimates are successively compared to surface-to-rock outcrop amplification spectra and are evaluated by deconvolution
of the downhole records based on the inversion results; comparison of the observed SSR and estimated surface-to-rock outcrop amplification spectra illustrates the effects
of destructive interference of downgoing waves at the downhole instrument level as a function of the site class. Site amplification factors are successively computed in reference to the National Earthquake Hazards Reduction Program (NEHRP) B–C boundary site conditions (V_(s30) = 760 m/sec), and results are compared to published values
developed on the basis of strong-motion data and site-response analyses. Finally, weak-motion SSR estimates are compared to the mainshock spectra, and conclusions
are drawn for the implications of soil nonlinearity in the near surface. Results presented in this article suggest that currently employed site classification criteria need
to be reevaluated to ensure intraclass consistency in the assessment of amplification potentials and nonlinearity susceptibility of near-surficial soil formations.