薄层时频特征的正演模拟

基于正演模拟的薄层时频特征响应分析是薄层定性识别与厚度定量预测的基础与关键.本文基于波场延拓理论,利用深度域相移法对不同厚度薄层进行了正演模拟.采用广义S变换对零偏移距地震道的反射复合波进行瞬时频谱分析,发现当薄层顶底反射系数极性相反时,复合波的干涉作用具有升频降幅作用,而极性相同时具有升幅降频作用;理论推导和实验分析均证明主峰值频率与薄层双程旅行时间厚度存在定量解析关系,这为薄层厚度定量预测提供了重要的技术手段;由于峰值频率对反射系数大小与极性变化不敏感,因此,峰值频率方法与时域振幅方法相比更具稳定性.

Forward modeling studies on the time-frequency characteristics of thin layers

The time-frequency response analysis based on forward modeling is a basis and key to qualitative determination and quantitative thickness prediction for thin layers. The thin layers with different thicknesses are modeled by phase-shift method based on the wave field extrapolation. The time-frequency responses on reflection composite wavelet from zero-offset trace are analyzed by generalized S transform. With the top and bottom reflection coefficients having an opposite polarity, the interference of reflection composite wavelet can lead to frequency elevation and amplitude decreasing. However, with the top and bottom reflection coefficients having an identical polarity, the interference of reflection composite wavelet can lead to amplitude elevation and frequency decreasing. The theoretical derivation and experimental analysis show that the peak frequency has a quantitative analytical relation with the two-way time thickness of reflection composite wavelet that can give a technological mean for predicting thin-layer thickness quantitatively. Since the peak frequency is not sensitive to the reflection coefficient, thin-layer thickness prediction of peak frequency method is a more stable than that of time-domain amplitude method.