Validation of 3-D basin structure models for long-period ground motion simulation in the Osaka basin, western Japan
Validation of 3-D basin structure models for long-period ground motion simulation in the Osaka basin, western Japan
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DOI：
10.1007/s10950-008-9088-0
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发表时间：
2008-02
影响因子：
1.6
通讯作者：
A. Iwaki;T. Iwata
中科院分区：
文献类型：
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作者：
A. Iwaki;T. Iwata
我们研究了现有的两种类型的三维（3-D）盆地速度结构模型的大坂盆地，日本西部的长期地面运动模拟的适用性。我们合成了长周期（3-20秒）的地面运动在大坂盆地M6.5地震发生在附近的假设东南海地震震源区，约200公里，从大坂。模拟采用三维有限差分法，非均匀交错网格，使用两个盆地的速度结构模型。为了研究盆地内的地震动特性，我们使用来自盆地和盆地外参考岩石场地的合成的传递函数来评估盆地内的波场。盆地现场的合成波形是通过计算的传递函数和参考岩石现场的观测波形的卷积获得的。首先，我们估计了沉积层的适当Q值。假设Q值取决于S波速度VS和周期T，则将其设置为Q =（1/3VS）（T0/T），其中VS的单位为m/s，参考周期T0为3.0 s。其次，我们比较了合成和观测波形和伪速度反应谱，以及两个盆地模型的速度结构的比较。我们还引入了拟合优度因子的拟速度反应谱作为客观指标。这两个模型的综合结果都较好地再现了盆地中部大部分台站的观测结果。然而，在某些站点，特别是在基岩深度变化剧烈的地方，模型的模拟结果存在明显的差异，合成数据不能准确地再现观测结果。我们的研究结果表明，一个模型优于其他不能确定和改进的盆地速度结构模型的基础上模拟研究是必要的，特别是沿着盆地边缘。我们还得出结论，我们的传递函数方法可用于检查盆地速度结构模型对长周期地面运动模拟的适用性。
We studied the applicability of two types of existing three-dimensional (3-D) basin velocity structure models of the Osaka basin, western Japan for long-period ground motion simulations. We synthesized long-period (3–20 s) ground motions in the Osaka basin during a M6.5 earthquake that occurred near the hypothetical Tonankai earthquake source area, approximately 200 km from Osaka. The simulations were performed using a 3-D finite-difference method with nonuniform staggered grids using the two basin velocity structure models. To study the ground motion characteristics inside the basin, we evaluated the wave field inside the basin using the transfer functions derived from the synthetics at the basin and a reference rock site outside the basin. The synthetic waveforms at the basin site were obtained by a convolution of the calculated transfer function and the observed waveform at the reference rock site.First, we estimated the appropriateQvalues for the sediment layers. Assuming that theQvalue depends on the S wave velocityVSand periodT, it was set toQ= (1/3VS)(T0/T) whereVSis in m/s and the reference periodT0is 3.0 s. Second, we compared the synthetics and the observations using waveforms and pseudovelocity response spectra, together with a comparison of the velocity structures of the two basin models. We also introduced a goodness-of-fit factor to the pseudovelocity response spectra as an objective index. The synthetics of both the models reproduced the observations reasonably well at most of the stations in the central part the basin. At some stations, however, especially where the bedrock depth varies sharply, there were noticeable discrepancies in the simulation results of the models, and the synthetics did not accurately reproduce the observation. Our results indicate that the superiority of one model over the other cannot be determined and that an improvement in the basin velocity structure models based on simulation studies is required, especially along the basin edges. We also conclude that our transfer function method can be used to examine the applicability of the basin velocity structure models for long-period ground motion simulations.