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首页> 外文期刊>Bulletin of the Seismological Society of America >Stochastic finite-fault modeling of ground motions from the 1999 Chi-Chi, Taiwan, earthquake: Application to rock and soil sites with implications for nonlinear site response
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Stochastic finite-fault modeling of ground motions from the 1999 Chi-Chi, Taiwan, earthquake: Application to rock and soil sites with implications for nonlinear site response

机译：台湾1999年Chi-Chi地震的地震动随机有限断层模拟：在岩石场地中的应用及其对非线性场地响应的影响

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The stochastic method for simulating strong ground motions from finite faults is applied to the records of the 1999 Chi-Chi, Taiwan, earthquake. The method involves discretization of the fault plane into smaller subfaults, each of which is assigned an omega(2) spectrum. The contributions from all subfaults are empirically attenuated to the observation site and summed to produce the synthetic acceleration time history. The method is initially calibrated against the data recorded at 24 rock sites, located within 7-120 km from the mainshock hypocenter and providing a broad azimuthal coverage of the fault plane. The accuracy of the simulations is quantified through the model bias, defined as the logarithm of the ratio of the observed to simulated spectrum, averaged over all stations. The calibrated model for the Chi-Chi event has a near-zero average bias in reproducing the ground motions at rock sites in the frequency range from 0.1 to 20 Hz. An unusually low value is found for the radiation-strength factors, controlling the high-frequency radiation level and directly related to the maximum slip velocity on the fault, compared with the mean value found for North American earthquakes. This result reflects the observed low peak ground accelerations of the Chi-Chi mainshock and, physically, its lower-than-usual slip velocities. The calibrated model is then used to simulate soil-site (site class D) records using the linear-response assumption. The simulated soil-site input motions are amplified by the weak-motion amplification functions, estimated by the spectral-ratio technique from available aftershock records. This analysis reveals an average reduction in strong-motion amplification to about 0.5-0.6 of that in weak motions, with an acceleration "threshold" for detectable nonlinearity near 200-300 cm/sec(2). However, the derivation of soil-site specific weak-motion amplification was limited by the amount of aftershock data available; further improvement in the quantification of nonlinear soil response during the Chi-Chi earthquake may be possible with the release of additional aftershock datasets. [References: 45]
机译：用于模拟有限断层强烈地面运动的随机方法被应用于台湾1999年集集地震的记录。该方法涉及将故障平面离散化为较小的子故障，每个子故障都分配有一个omega（2）频谱。所有子故障的贡献将根据经验衰减到观测点，并相加以产生合成加速时间历史。该方法最初针对在距主震震源7-120 km之内的24个岩石站点记录的数据进行了校准，并提供了断层平面的广泛方位角覆盖。通过模型偏差量化仿真的准确性，模型偏差定义为在所有站点上平均的观测频谱与仿真频谱之比的对数。 Chi-Chi事件的校准模型在再现频率范围从0.1到20 Hz的岩石场所的地面运动时，具有接近零的平均偏差。与北美地震的平均值相比，发现了辐射强度因子的异常低值，该值控制了高频辐射水平，并且与断层的最大滑动速度直接相关。该结果反映了所观察到的Chi-Chi主冲击的低峰值地面加速度，以及其物理上低于平常的滑移速度。然后，使用线性响应假设，将校准后的模型用于模拟土壤站点（站点类别D）的记录。模拟的土壤现场输入运动通过弱运动放大函数进行放大，该函数通过频谱比技术从可用的余震记录中进行估算。该分析揭示了强运动放大的平均减少量约为弱运动的平均减少量的0.5-0.6，在200-300 cm / sec（2）附近具有可检测到的非线性加速度“阈值”（2）。但是，土壤位点特定的弱运动放大的推导受到了余震数据数量的限制。通过发布其他余震数据集，可能会进一步改善Chi-Chi地震期间非线性土壤响应的量化。 [参考：45]

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