Ground‐motion records are critical for seismic hazard assessment and seismic design of buildings and infrastructures. Large (⁠>1g⁠), asymmetric vertical accelerations (AsVAs) have been observed at strong‐motion stations during recent earthquakes. However, it is not clear whether all of the observed AsVAs reflect actual ground shaking or the interaction of a building structure and underlying ground. Here, we investigate the cause of large AsVAs recorded at several seismic stations in Christchurch, New Zealand, during the 2011 Mw 6.2 Christchurch earthquake. We first define three metrics and quantify the degree of waveform asymmetry in all available records from nearby M>3 earthquakes. Histograms of the metrics show greater waveform asymmetry for larger accelerations at these stations, which is consistent with the prediction of a nonlinear, soil–structure interaction associated with the elastic collisions of a foundation slab onto the underlying soil. We then use finite‐element models to examine the occurrence of the nonlinear, soil–structure interaction at these stations during the Mw 6.2 mainshock and Mw 5.6 aftershock of the 2011 Christchurch earthquake. The parameters of the numerical models are constrained by site investigation of selected stations. We find that numerical simulations closely reproduce the large AsVAs recorded at stations HVSC and PRPC, suggesting that these ground‐motion records were contaminated by the nonlinear, soil–structure interaction. Seismic sensors located near the corner of a concrete slab are shown to be more prone to this phenomenon. Our results further suggest that artificial recording of large AsVAs due to the nonlinear, soil–structure interaction can be mitigated if a seismic sensor is placed closer to the center of a foundation slab. The analytical procedure presented in this study may be useful in identifying the occurrence of AsVAs elsewhere and in assessing whether AsVAs are caused by the nonlinear, soil–structure interaction.

中文翻译：

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2011年克赖斯特彻奇地震序列中的极端地面加速度被非线性的土壤与结构相互作用所污染的记录

地面运动记录对于地震危险性评估以及建筑物和基础设施的地震设计至关重要。在最近的地震中，强运动台站观测到较大的（⁠>1g⁠）不对称垂直加速度（AsVA）。但是，尚不清楚是否所有观察到的AsVA都反映了实际的地面震动或建筑物结构与底层地面的相互作用。在此，我们调查了2011年克赖斯特彻奇6.2级地震期间在新西兰克赖斯特彻奇的几个地震台站记录到的大量AsVA的原因。我们首先定义三个指标，并对附近M> 3地震的所有可用记录中的波形不对称程度进行量化。指标的直方图显示这些站的加速度更大时，波形不对称性也更大，这与非线性，与基础平板弹性碰撞到地下土壤相关的土壤-结构相互作用。然后，我们使用有限元模型研究了2011年克赖斯特彻奇地震的6.2级主地震和5.6级余震在这些站点上非线性，土-结构相互作用的发生。数值模型的参数受所选站点的现场调查的约束。我们发现，数值模拟紧密地再现了在HVSC和PRPC站上记录的大型AsVA，这表明这些地面运动记录受到非线性，土壤-结构相互作用的污染。靠近混凝土板一角的地震传感器显示出更容易出现这种现象。我们的结果进一步表明，由于非线性，如果将地震传感器放置在靠近基础平板中心的位置，则可以减轻土壤与结构的相互作用。这项研究中提出的分析程序可能对识别其他地方的AsVAs的发生以及评估AsVAs是否是由非线性的土壤-结构相互作用所引起的有用。