The results may better reflect the non-stationarity of ground motion in time domain and are closer to reality than those by wave theory and stationary random vibration theory.
由于这种方法能较好地反映地面运动的时域非平稳性，所以得到的计算结果更真实。
2
Consequently, it is necessary to describe earthquake ground motion with local spectral density, which is time-dependent and can reflect the non-stationary characteristics.
因此采用能反映时频非平稳特性的时变谱密度(即局部谱密度)来描述地震地面运动是非常必要的。
3
Utilizing these statistical features, we can simulate the design ground motion founded on the theories of non-stationary time history.