高频衰减参数(k)的研究——以伊朗强震数据为例

Study on the High Frequency Attenuation Parameter (k)—A Case Study of Strong Earthquake Data in Iran

摘要: Kappa (k)值参数是控制高频率地面震动的一个重要参数，该参数是加速度傅里叶谱在一定频率范围内线性对数尺度上的线性衰减因子，表示高频能量的衰减范围。该参数通过随机方法作为模拟强地震动的关键输入。本研究旨在估算伊朗西部高地震活动性地区的kappa参数。因此，我们使用了1973年至2018年期间记录的10次参考地震和76次加速度记录，包括2017年11月12日克尔曼沙发生的7.3级Ezgeleh地震。为提高计算精度，在伊朗最新的地震构造分区图中导出了k，k方程只考虑了在同一区域发生的参考地震和加速度记录。分别计算每个水平分量k值的均值。然后，分别计算并分析了各地震带k值与距离的线性关系。并提出了各区域的累积方程。给出的方程表明，近地表衰减参数k₀伊朗西部地震带的变化范围为0.0331~0.0398。利用该参数可以有效地用综合方法计算该区的强地震动。

Abstract: An important parameter that controls strong ground motion at high frequencies (higher than 1 Hz) is the spectral decay or kappa (k) parameter. This parameter is a linear decay factor for Fourier spectrum of acceleration on a linear-logarithmic scale within a certain frequency range, which indicates the range of attenuation of high frequency energy. This parameter is used as a key input for the simulation of strong ground motion through a random method. This study aims to estimate the kappa parameter for the west of Iran that has a high seismic activity. Hence 10 reference earthquakes as well as 76 accelerograms recorded from 1973 until 2018 are used, including the 7.3-magnitude Ezgeleh, Kermanshah earthquake on November 12, 2017. The k is derived for the latest seismotectonic zoning map of Iran to enhance the accuracy of calculations and only the records in which the reference earthquake and accelerograms occurred in the same zone are considered in the k equation. The k parameter is calculated separately for each horizontal component and for the mean. Then, the linear relationships between the kappa and distance are separately calculated and analyzed for each seismic zone. An accumulative equation is also proposed for all zones. The presented equations indicate that the near surface attenuation parameter k₀ for the west seismic zones of Iran varies from 0.0331 to 0.0398. This parameter can be used effectively to calculate the strong ground motion in the zones using synthetic methods.