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当经验格林函数法应用于软土层上的观测点所记录的地震图时,有必要考虑软土层的非线性行为。实践中,经常假定地震波只在入射到局部软土层后才受到土壤非线性的影响。然而,如果我们考虑连接震源和测点的地震射线,地震射线穿过软土层若干次也许是真实的。因此,在地震波由震源传播到接收点时,假设地震波受到土层非线性影响若干次是合理的。这一可能的现象就是本文所指的“多重非线性效应”。在经验格林函数法中考虑这些效应,笔者提出用“非线性参数”表示由于土层的非线性导致的沉积层介质特性对线性状态的偏差,同时用于修正格林函数。这些参数用于2000年鸟取县西部地震和1995年兵库县南部地震的地震动模拟。发现,尽管新参数十分简单,但对改善模拟结果却很有帮助。
When the empirical Green’s function method is applied to the seismograms recorded at the observation points on the soft soil layer, it is necessary to consider the nonlinear behavior of the soft soil layer. In practice, it is often assumed that seismic waves are not affected by soil nonlinearity only after they have been incident on a local soft soil layer. However, if we consider the seismic ray connecting the source and the measuring point, it may be true that the seismic ray traverses the soft soil several times. Therefore, when seismic waves propagate from the source to the receiving point, it is reasonable to assume that the seismic waves are affected several times by the soil nonlinearity. This possible phenomenon is referred to herein as “multiple nonlinear effects.” Taking these effects into account in empirical Green’s function method, the author proposes that “nonlinear parameter” be used to denote the deviation of linearity caused by the nonlinearity of sedimentary layer and the Green’s function. These parameters are used to simulate the earthquakes in the west of Tottori in 2000 and the earthquake in southern Hyogo in 1995. Found that although the new parameters were simple, they were helpful to improve the simulation results.