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首页> 外文期刊>Frontiers in Built Environment >Overview of Ground-Motion Issues for Cascadia Megathrust Events: Simulation of Ground-Motions and Earthquake Site Response
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Overview of Ground-Motion Issues for Cascadia Megathrust Events: Simulation of Ground-Motions and Earthquake Site Response

机译：卡斯卡迪亚特大推力事件的地震动问题概述：地震动和地震场响应的模拟

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Ground motions for earthquakes of M7.5 to 9.0 on the Cascadia subduction interface are simulated based on a stochastic finite-fault model, and used to estimate average response spectra for reference firm soil conditions. The simulations are first validated by modeling the wealth of ground-motion data from the the 2011 M9.0 Tohoku earthquake of Japan. Adjustments to the calibrated model are then made to consider average source, attenuation and site parameters for the Cascadia region. This includes an evaluation of the likely variability in stress drop for large interface earthquakes, and an assessment of regional attenuation and site effects. We perform best-estimate simulations for a preferred set of input parameters. Typical results suggest mean values of 5%-damped pseudo-acceleration in the range from about 100 to 200 cm/s2, at frequencies from 1 to 4 Hz, for firm-ground conditions in Vancouver. Uncertainty in most-likely value of the parameter representing stress drop causes variability in simulated response spectra of about ±50%. Uncertainties in the attenuation model produce even larger variability in response spectral amplitudes a?? a factor of about two at a closest distance to the rupture plane (Rcd) of 100 km, becoming even larger at greater distances. It is thus important to establish the regional attenuation model for ground-motion simulations, and to bound the source properties controlling radiation of ground motion. We calculate theoretical 1D spectral amplification estimates for four selected Fraser River Delta sites to show how the presence of softer sediments in the region may alter the predicted ground motions. The amplification functions are largely consistent with observed spectral amplification at Fraser River delta sites, suggesting amplification by factors of 2.5 to 5 at the peak frequency of the site; we note that deep sites in the delta have a low peak frequency, ~0.3 Hz. This work will aid in seismic hazard assessment and mitigation efforts in the active Cascadia region of southwestern B.C. An important consideration is that the uncertainties are large and present a dominant unknown when assessing seismic risk. We find that variability in the expected motions exceeds a factor of two even on rock-like sites, with uncertainty.
机译：基于随机有限故障模型，模拟了卡斯卡迪亚俯冲界面上M7.5至9.0级地震的地震动，并用于估算参考坚硬土壤条件的平均响应谱。首先通过对来自2011年日本东北部M9.0地震的大量地面运动数据进行建模来对模拟进行验证。然后对校准模型进行调整，以考虑卡斯卡迪亚地区的平均震源，衰减和场地参数。这包括评估大界面地震时应力下降的可能变化，以及评估区域衰减和场地效应。我们对一组首选的输入参数执行最佳估计的模拟。典型结果表明，对于温哥华的牢固地面条件，在1至4 Hz的频率下，阻尼为5％的伪加速度的平均值在大约100至200 cm / s2的范围内。代表应力下降的参数最可能的值不确定性会导致模拟响应谱中的变化约为±50％。衰减模型的不确定性会在响应频谱幅度a 10中产生更大的变化。距破裂平面（Rcd）最接近的距离100 km的系数大约为2，在更大的距离处甚至更大。因此，重要的是建立用于地震动模拟的区域衰减模型，并限制控制地震动辐射的源特性。我们计算了四个选定的弗雷泽河三角洲站点的理论一维光谱放大估计，以显示该地区较软的沉积物的存在可能如何改变预测的地面运动。放大函数与在弗雷泽河三角洲地区观测到的光谱放大率基本一致，表明该地点峰值频率的放大系数为2.5到5。我们注意到，三角洲深处的峰值频率较低，约为0.3 Hz。这项工作将有助于BC省西南部活跃的卡斯卡迪亚地区的地震灾害评估和减灾工作。一个重要的考虑因素是不确定性很大，并且在评估地震风险时存在显着的未知数。我们发现，即使在类似岩石的站点上，预期运动的可变性也超过了两倍，并且具有不确定性。

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