Zhang Xinrui, Morikawa Hitoshi
Department of Built Environment, Tokyo Institute of Technology, W8-22, 2-12-1, Ookayama, Meguro-ku, Tokyo, 152-8552 Japan.
J Seismol. 2016;20(1):185-196. doi: 10.1007/s10950-015-9519-7. Epub 2015 Sep 5.
Array methods like spatial auto-correlation (SPAC) method and the centerless circular array (CCA) method have provided a convenient means of inferring the phase velocity of surface waves. However, these methods are under the assumption of horizontally layered medium (lateral homogeneity) while the ground structure is actually likely to be inclined. Hence, it is expected to obtain more detailed information of ground structure such as inclination by making better use of the records. In recent years, the seismic interferometry theory has also been widely used to estimate ground structure. According to seismic interferometry theory, the cross correlation of motion between two sites is proportional to the imaginary part of the Green's function (IOG) between the two sites in diffuse wavefield. In this study, we can obtain the ratio of IOG between two sites by taking the ratio of power spectra between the same two sites. We propose this ratio as an indicator of the lateral heterogeneity between two sites. Through numerical simulation and a field test, we demonstrate that the significance of ratio of power spectra can be interpreted from the sight of ratio of IOG successfully.
诸如空间自相关（SPAC）方法和无中心圆形阵列（CCA）方法等阵列方法为推断面波的相速度提供了一种便捷手段。然而，这些方法是基于水平分层介质（横向均匀性）的假设，而实际的地面结构可能是倾斜的。因此，期望通过更好地利用记录来获取诸如倾斜度等更详细的地面结构信息。近年来，地震干涉测量理论也被广泛用于估计地面结构。根据地震干涉测量理论，在漫射波场中，两个场地之间运动的互相关与两个场地之间格林函数的虚部（IOG）成正比。在本研究中，我们可以通过获取相同两个场地之间的功率谱之比来得到两个场地之间IOG的比值。我们提出将这个比值作为两个场地之间横向非均匀性的一个指标。通过数值模拟和现场试验，我们成功地证明了可以从IOG比值的角度来解释功率谱比值的意义。
