The spectral decay parameter of the amplitudes of high-frequency ground motion, Kappa (k), is widely used in many seismological and earthquake engineering studies. This parameter is dependent on the local characteristics of the site, the propagation path, and the earthquake source. In this paper, the values of k and its variation with subsurface anisotropy and the direction of energy propagation of seismic waves at the source are studied. For this purpose, k values for 508 accelerograms of 141 earthquakes with a moment magnitudes between M_w 3.3 to 7 and epicentral distances less than 100 km are calculated. Various portions of records (P- and S-wave) are used. Records were collected at 20 surface and borehole accelerometery stations of KiK-net strong-motion seismograph networks of Japan’s National Research Institute for Earth Science and Disaster (NIED). Our results show that for all the wave segments considered in this study, k values for the horizontal component are larger than the vertical component at surface stations. In addition, the estimated value of this parameter for surface stations is greater than that of the borehole stations. Differences in k values for the surface and the borehole records also show that k values for S-wave are greater than of the P-wave. The effect of the radiation pattern of seismic waves and source directivity on the k values is another parameter that assessed for our database. The results of this study clearly show that the k changes with the angle at which the wave reaches the station.

高频地震动振幅的频谱衰减参数Kappa（k）被广泛用于许多地震和地震工程研究中。此参数取决于站点的局部特征，传播路径和地震源。本文研究了k的值及其随地下各向异性的变化以及震源处能量传播的方向。为此，矩量在M _w之间的141次地震的508个加速度图的k值计算得出3.3至7，震中距离小于100 km。使用记录的各个部分（P波和S波）。在日本国立地球科学与灾难研究所（NIED）的KiK-net强运动地震仪网络的20个地面和钻孔加速度计站点上收集了记录。我们的结果表明，对于本研究中考虑的所有波段，水平面站的水平分量的k值都大于垂直分量的k值。另外，该参数对于地面站的估计值大于钻孔站点的估计值。地表和钻孔记录的k值差异也表明kS波的值大于P波的值。地震波的辐射方向图和震源指向性对k值的影响是为我们的数据库评估的另一个参数。这项研究的结果清楚地表明，k随波到达电台的角度而变化。