THE PROCEDURE OF FILTERING THE STRONG MOTION RECORD: DENOISING AND FILTERING
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摘要: 强震动记录一直以来被用于工程结构弹塑性时程分析的地震动输入，其由仪器观测获得，需在使用前进行必要的数据处理工作。中国台网目前已累积了大量强震动观测记录，但始终缺乏标准化的数据处理流程，给使用者造成了诸多不便，不能最大程度发挥其科学应用价值。该文针对我国观测数据现状，提出了一套完整的面向工程应用的强震动记录数据处理流程，给出了高通滤波截止频率的选取原则，包括：记录的傅里叶振幅谱低频段须符合w2震源模型、信噪比须大于3、确保与物理分辨率一致。研究了因果滤波与非因果滤波对记录时程的影响，结果表明：这两种滤波方式具有各自特性，因果滤波会引起记录相变、而非因果滤波则会引起信号前干扰震动；针对芦山地震数据集及2017年部分观测记录，研究了这两种滤波方式对伪加速度反应谱(PSA)的影响，结果表明因果滤波引起的相变会对有效周期范围内的PSA造成计算偏差，因此建议面向工程应用的强震动记录选用非因果滤波方式。此项工作有助于指导和规范强震动记录的合理使用。Abstract: Strong motion records of ground have been used as the ground motion input for the elastic-plastic time series analysis of engineering structures. It requires necessary data processing before used, as they are obtained by instrumental observations. Many strong motion records of ground have been accumulated in China, but there is a lack of standardized procedure of data processing, causing some inconveniences to users and devaluating their scientific applications. A complete procedure of data processing for the strong motion record of ground is proposed, which will be particularly used in engineering practice. Three principles for selecting the cut-off frequency of high-pass filtering are suggested, including that the low-frequency Fourier amplitude spectrum must conform to the w2 source model, that the signal-to-noise ratio must be greater than 3, and that the physical resolution keeps consistent. The effects of causal and acausal filtering on the recorded time series are investigated. The results show that these two approaches have their own characteristics, causal filtering causes phase shift and acausal filtering causes interference vibration before signal arrives. The effects of causal and acausal filtering on the pseudo acceleration response spectrum are investigated using data collected in Lushan earthquake in 2013 together with some data recorded in 2017. It shows that the phase shift caused by causal filtering can cause bias in the calculation of PSA in the effective period range. Thusly, it is recommended to use acausal filtering for strong motion records used in engineering practice. It could help to guide the use of strong motion records of ground in an appropriate way.
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图 1 本文给出的强震动记录数据处理流程
Figure 1. A flow chart for data processing of strong motion record suggested by this study
2 脉冲信号经因果和非因果滤波后振幅及相位对比结果
2. Comparisons of amplitude and phase of an impulse signal produced by causal and acausal filtering
图 3 典型记录经因果和非因果滤波后加速度、速度和位移时程比较(右图为左图阴影区域的局部放大)
Figure 3. Comparisons of acceleration, velocity and displacement time-series of a typical record processing by causal and acausal filtering (right figure represents a local zoom-in picture)
图 4 选取的数据集记录在因果和非因果滤波后加速度、速度和位移时程与原始时程的相关系数
Figure 4. Correlation coefficients of the original acceleration, velocity and displacement time-series in the dataset with those processing by causal and acausal filtering
图 5 典型记录经因果和非因果滤波处理后位移时程比较以及识别的P波到时与S波到时比较
Figure 5. Comparison of displacement time-series and P-wave and S-wave onsets of a typical record processing by causal and acausal filtering
图 6 典型有噪声窗的强震动记录fHP选取过程示意以及因果滤波后位移时程合理性评判
Figure 6. Illustration of the fHP selection for a typical record with noise window and the rationality judgement of displacement time-series after a causal filtering
图 7 典型无噪声窗强震动记录fHP选取过程示意以及因果滤波后位移时程合理性判断
Figure 7. Illustration of the fHP selection for a typical record without noise window and the rationality judgement of displacement time-series after a causal filtering
图 8 典型记录在因果滤波和非因果滤波前、后的拟加速度反应谱对比
Figure 8. Comparison of the pseudo spectral accelerations of a typical record before and after its causal and acausal filtering
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